BS EN 752:2008 Drain and Sewer Systems Outside Buildings

BS EN
EN
752:2008
752:2008
BRITISH STANDARD
Incorporating
Incorporating
Corrigenda
Corrigendum
October
October 2009
2009 and
November 2013
Drain and sewer
systems outside
buildings
ICS 93.030
BS EN
BS
EN 752:2008
752:2008
National foreword
This British Standard is the UK implementation of EN 752:2008. It supersedes
BS EN 752, Parts 1 to 7, which have been withdrawn.
The UK participation in its preparation was entrusted to Technical Committee
B/505, Wastewater engineering.
A list of organizations represented on this committee can be obtained on
request to its secretary.
The British Standard contains both the text of the European Standard together
with a National Annex, which gives further UK-specific guidance on the
application of the European text. The European Standard should therefore be
read in conjunction with the National Annex and, to assist in this, cross
references to the clauses in the European text are included in the headings in
the National Annex.
This revision of EN 752 includes some important and timely changes. It takes
a more integrated view of sewer system management in the context of the
wider urban drainage system and the wider water environment. This both
supports the current initiative on integrated urban drainage management in
the UK and is essential for the proper implementation of the Water Framework
Directive. In response to climate change, the European text introduces the
concept of exceedence flood risk assessment and further UK guidance on this
is given in the National Annex.
This publication does not purport to include all the necessary provisions of a
contract. Users are responsible for its correct application.
Compliance with a British Standard cannot confer immunity from
legal obligations.
This British Standard was
published under the authority
of theBritish
Standards
Policywas
and
This
Standard
Strategy
Committee
published under the authority
onthe
30 April
2008 Policy and
of
Standards
Strategy Committee
on 30 April 2008
© The British Standards
Institution 2013.
Published by BSI Standards
Limited
2013
9
©
BSI 200
ISBN
ISBN 978
978 00 580
580 69252
84887 92
Amendments/corrigenda issued since publication
Date
Comments
Amendments/corrigenda
issued since publication
31 October 2009
Date
Correction to N.A 5.8, value b
Comments
31 October 2009
Correction to N.A 5.8, value b
30 November 2013
National Annex NA revised
EN 752
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2008
ICS 93.030
Supersedes EN 752-1:1995, EN 752-2:1996, EN 7523:1996, EN 752-4:1997, EN 752-5:1997, EN 752-6:1998,
EN 752-7:1998
English Version
Drain and sewer systems outside buildings
Réseaux d'évacuation et d'assainissement à l'extérieur des
bâtiments
Entwässerungssysteme außerhalb von Gebäuden
This European Standard was approved by CEN on 24 November 2007.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36
© 2008 CEN
All rights of exploitation in any form and by any means reserved
worldwide for CEN national Members.
B-1050 Brussels
Ref. No. EN 752:2008: E
BS EN 752:2008
EN 752:2008 (E)
Foreword
Contents
BS EN 752:2008
EN 752:2008 (E)
Page
This document (EN 752:2008) has been prepared by Technical Committee CEN/TC 165 “Wastewater
Foreword..............................................................................................................................................................7
Engineering”, the secretariat of which is held by DIN.
1
Scope ....................................................................................................................................................10
This European Standard shall be given the status of a national standard, either by publication of an identical
2
Normative references ..........................................................................................................................10
text or by endorsement, at the latest by July 2008, and conflicting national standards shall be withdrawn at the
latest
byTerms
July 2008.
3
and definitions .........................................................................................................................11
4
Objectives.............................................................................................................................................19
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
4.1
General..................................................................................................................................................19
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
4.2
Public Health and Safety.....................................................................................................................20
4.3
Occupational Health and Safety.........................................................................................................20
This document supersedes EN 752-1:1995, EN 752-2:1996, EN 752-3:1996, EN 752-4:1997, EN 752-5:1997,
4.4
Environmental Protection ...................................................................................................................20
EN 752-6:1998, EN 752-7:1998.
4.5
Sustainable Development ...................................................................................................................20
5
Requirements
.......................................................................................................................................21
According
to the CEN/CENELEC
Internal Regulations, the national standards organizations of the following
5.1
Functional
Requirements....................................................................................................................21
countries
are bound
to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
5.1.1 Introduction
..........................................................................................................................................21
Republic,
Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
5.1.2 Protection
fromMalta,
flooding
.....................................................................................................................22
Lithuania,
Luxembourg,
Netherlands,
Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
5.1.3 Maintainability
......................................................................................................................................22
Sweden,
Switzerland and
the United Kingdom.
5.1.4 Protection of surface receiving waters .............................................................................................22
5.1.5 Protection of groundwater..................................................................................................................22
5.1.6 Prevention of odours and toxic, explosive and corrosive gases ...................................................23
5.1.7 Prevention of noise and vibration......................................................................................................23
5.1.8 Sustainable use of products and materials ......................................................................................23
5.1.9 Sustainable use of energy ..................................................................................................................23
5.1.10 Structural integrity and design life ....................................................................................................23
5.1.11 Maintaining the flow ............................................................................................................................23
5.1.12 Watertightness .....................................................................................................................................23
5.1.13 Not endangering adjacent structures and utility services ..............................................................23
5.1.14 Inputs quality........................................................................................................................................23
5.2
Determination of performance requirements for the drain and sewer system .............................23
6
6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
6.2.10
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.3.7
6.3.8
2
Integrated Sewer System Management .............................................................................................26
Introduction ..........................................................................................................................................26
Investigation.........................................................................................................................................27
Introduction ..........................................................................................................................................27
Purpose of investigation .....................................................................................................................28
Review of performance information ..................................................................................................28
Determine the scope of the investigation .........................................................................................30
Review existing information ...............................................................................................................30
Inventory update ..................................................................................................................................31
Hydraulic investigation .......................................................................................................................31
Environmental investigation...............................................................................................................31
Structural investigation.......................................................................................................................32
Operational Investigation....................................................................................................................32
Assessment..........................................................................................................................................33
Introduction ..........................................................................................................................................33
Assessment of the hydraulic performance.......................................................................................33
Assessment of environmental impact ...............................................................................................33
Assess structural condition ...............................................................................................................34
Assess operational performance .......................................................................................................34
Compare with performance requirements ........................................................................................34
Identify unacceptable impacts ...........................................................................................................34
Identify causes of performance deficiencies....................................................................................34
7
BS EN 752:2008
EN 752:2008
(E)
BS
EN 752:2008
EN 752:2008 (E)
BS EN 752:2008
EN 752:2008 (E)
6.4
Developing the Plan ............................................................................................................................34
6.4.1 Introduction..........................................................................................................................................34
6.4.2 Develop integrated solutions .............................................................................................................35
6.4.3 Assess Solutions.................................................................................................................................38
Contents
Page
6.4.4 Prepare action plan .............................................................................................................................39
Contents
Page
6.5
Implementation ....................................................................................................................................40
Foreword..............................................................................................................................................................7
6.5.1 Introduction..........................................................................................................................................40
6.5.2 Carry out work .....................................................................................................................................40
Foreword..............................................................................................................................................................7
1
Scope ....................................................................................................................................................10
6.5.3 Monitoring performance .....................................................................................................................41
1
6.5.4 Scope
Review....................................................................................................................................................10
performance
and update plan.......................................................................41
2
Normative
referencesrequirements
..........................................................................................................................10
2
7
3
Normative
..........................................................................................................................10
Health and references
Safety Principles
..............................................................................................................41
Terms
definitions
.........................................................................................................................11
3
8
4
8.1
4.1
4
8.2
4.2
4.1
8.3
4.3
4.2
8.4
4.4
4.3
8.4.1
4.5
4.4
8.4.2
4.5
5
8.4.3
5.1
5
8.4.4
5.1.1
5.1
8.5
5.1.2
5.1.1
8.5.1
5.1.3
5.1.2
8.5.2
5.1.4
5.1.3
8.5.3
5.1.5
5.1.4
8.5.4
5.1.6
5.1.5
8.5.5
5.1.7
5.1.6
8.5.6
5.1.8
5.1.7
8.6
5.1.9
5.1.8
8.6.1
5.1.10
5.1.9
8.6.2
5.1.11
5.1.10
8.6.3
5.1.12
5.1.11
8.6.4
5.1.13
5.1.12
8.7
5.1.14
5.1.13
8.7.1
5.2
5.1.14
8.7.2
5.2
8.7.3
6
8.7.4
6.1
6
6.2
6.1
9
6.2.1
6.2
9.1
6.2.2
6.2.1
9.2
6.2.3
6.2.2
9.2.1
6.2.4
6.2.3
9.2.2
6.2.5
6.2.4
9.2.3
6.2.6
6.2.5
9.2.4
6.2.7
6.2.6
9.2.5
6.2.8
6.2.7
9.2.6
6.2.9
6.2.8
9.3
6.2.10
6.2.9
9.3.1
6.3
6.2.10
9.3.2
6.3.1
6.3
9.3.3
6.3.2
6.3.1
9.3.4
6.3.3
6.3.2
9.3.5
6.3.4
6.3.3
9.3.6
6.3.5
6.3.4
9.3.7
6.3.6
6.3.5
9.4
6.3.7
6.3.6
9.4.1
6.3.8
6.3.7
9.4.2
6.3.8
9.4.3
Terms
definitions
.........................................................................................................................11
Designand
Principles
................................................................................................................................42
Objectives.............................................................................................................................................19
General .................................................................................................................................................42
General..................................................................................................................................................19
Objectives.............................................................................................................................................19
Types of
systems
................................................................................................................................42
Public
Health
and Safety.....................................................................................................................20
General..................................................................................................................................................19
Layout
and
profile
...............................................................................................................................43
Occupational
Health
and Safety.........................................................................................................20
Public Health and Safety.....................................................................................................................20
Hydraulic Design
.................................................................................................................................44
Environmental
Protection
...................................................................................................................20
Occupational Health and Safety.........................................................................................................20
General .................................................................................................................................................44
Sustainable
Development
...................................................................................................................20
Environmental Protection ...................................................................................................................20
Foul drains and sewers.......................................................................................................................44
Sustainable
Development
...................................................................................................................20
Requirements
.......................................................................................................................................21
Surface water drains and sewers ......................................................................................................45
Functional Requirements....................................................................................................................21
Requirements
.......................................................................................................................................21
Combined drains
and sewers ............................................................................................................47
IntroductionRequirements....................................................................................................................21
..........................................................................................................................................21
Functional
Environmental Considerations ..........................................................................................................47
Protection
from
flooding .....................................................................................................................22
Introduction
..........................................................................................................................................21
General .................................................................................................................................................47
Maintainability
......................................................................................................................................22
Protection of
from
flooding
.....................................................................................................................22
surface
receiving
waters .............................................................................................49
Protection
of surface
receiving waters .............................................................................................22
Maintainability
......................................................................................................................................22
Protection of Groundwater
.................................................................................................................49
Protection of
of groundwater..................................................................................................................22
Protection
waters .............................................................................................22
Prevention of surface
septicityreceiving
........................................................................................................................49
Prevention
of groundwater..................................................................................................................22
odours and toxic, explosive and corrosive gases ...................................................23
Protection
of
Combined sewer
overflows and surface water treatment...............................................................50
Prevention of
of odours
noise and
vibration......................................................................................................23
Prevention
and
toxic, explosive and corrosive gases ...................................................23
Emergency overflows
.........................................................................................................................50
Sustainable
use
of
products
and materials ......................................................................................23
Prevention
of noise and vibration......................................................................................................23
Structural Design.................................................................................................................................50
Sustainable
use
of
energy
..................................................................................................................23
Sustainable
use of products and materials ......................................................................................23
Introduction..........................................................................................................................................50
Structural
integrity
and design
life ....................................................................................................23
Sustainable
use ofofenergy
..................................................................................................................23
Structural design
pipelines
............................................................................................................51
Maintaining
the
flow
............................................................................................................................23
Structural integrity
design
life ....................................................................................................23
design ofand
other
components
............................................................................................51
Watertightness
Maintaining
the.....................................................................................................................................23
flow..............................................................................................................................51
............................................................................................................................23
Materials selection
Not endangering
adjacent structures and utility services ..............................................................23
Watertightness
.....................................................................................................................................23
Operational Considerations
...............................................................................................................52
Inputs
quality........................................................................................................................................23
Not
endangering
adjacent structures and utility services ..............................................................23
General
.................................................................................................................................................52
Determination
of performance requirements for the drain and sewer system .............................23
Inputs
quality........................................................................................................................................23
Separators
............................................................................................................................................52
Determination
of
performance
requirements for the drain and sewer system .............................23
Self-cleansing
conditions
...................................................................................................................52
Integrated
Sewer
System Management.............................................................................................26
Access to drains
and sewers .............................................................................................................53
Introduction
..........................................................................................................................................26
Integrated Sewer System Management.............................................................................................26
Investigation.........................................................................................................................................27
Introduction
..........................................................................................................................................26
Detailed Design....................................................................................................................................53
Introduction ..........................................................................................................................................27
Investigation.........................................................................................................................................27
Introduction..........................................................................................................................................53
Purpose
of investigation
.....................................................................................................................28
Introduction
..........................................................................................................................................27
Layout and profile
...............................................................................................................................53
Review
of
performance
information
..................................................................................................28
Purpose
of investigation .....................................................................................................................28
Introduction..........................................................................................................................................53
Determine
the
scope
of
the
investigation
.........................................................................................30
Review
of performance information ..................................................................................................28
Layout ...................................................................................................................................................53
Review
existing
information
...............................................................................................................30
Determine
the scope of the investigation .........................................................................................30
Accessibility.........................................................................................................................................54
Inventory
updateinformation
..................................................................................................................................31
Review
existing
...............................................................................................................30
Depth.....................................................................................................................................................54
Hydraulic
investigation
.......................................................................................................................31
Inventory
update ..................................................................................................................................31
Need for pumping................................................................................................................................55
Environmental
investigation...............................................................................................................31
Hydraulic
investigation
.......................................................................................................................31
Pumping Installations
.........................................................................................................................55
Structural
investigation.......................................................................................................................32
Environmental
investigation...............................................................................................................31
Preliminary Investigations..................................................................................................................56
Operational
Investigation....................................................................................................................32
Structural
investigation.......................................................................................................................32
General .................................................................................................................................................56
Assessment..........................................................................................................................................33
Operational
Investigation....................................................................................................................32
Topography..........................................................................................................................................56
Introduction ..........................................................................................................................................33
Assessment..........................................................................................................................................33
Geotechnical Survey ...........................................................................................................................56
Assessment
of the hydraulic performance.......................................................................................33
Introduction
Groundwater..........................................................................................................................................33
........................................................................................................................................57
Assessment
of
impact ...............................................................................................33
Assessment
of environmental
theservices
hydraulic
performance.......................................................................................33
Existing drainage
.................................................................................................................57
Assess
structural
condition
...............................................................................................................34
Assessment
ofutility
environmental
impact ...............................................................................................33
Other existing
services ............................................................................................................57
Assess
operational
performance
.......................................................................................................34
Assess
structural
condition
...............................................................................................................34
Extraneous
water.................................................................................................................................57
Compare
with
performance
requirements
........................................................................................34
Assess
operational
performance .......................................................................................................34
Hydraulic
Design .................................................................................................................................57
Identify
unacceptable
impacts
...........................................................................................................34
Compare
with performance requirements ........................................................................................34
Introduction..........................................................................................................................................57
Identify causes
of performance
deficiencies....................................................................................34
Identify
unacceptable
impacts ...........................................................................................................34
Foul drains
and sewers.......................................................................................................................57
Identify
of performance
deficiencies....................................................................................34
Surface causes
water drains
and sewers
......................................................................................................58
2
2
3
BS EN 752:2008
EN 752:2008 (E)
6.4
9.4.4
6.4.1
9.4.5
6.4.2
9.4.6
6.4.3
9.4.7
6.4.4
9.5
6.5
9.5.1
6.5.1
9.5.2
6.5.2
9.5.3
6.5.3
9.5.4
6.5.4
9.6
BS EN 752:2008
EN 752:2008 (E)
Developing
the Plan
Combined drains
and............................................................................................................................34
sewers.............................................................................................................58
Introduction..........................................................................................................................................34
Capacity of pipelines ...........................................................................................................................59
Develop
integrated
solutions..............................................................................................................59
.............................................................................................................35
Sewers with
steep gradients
Assess
Solutions.................................................................................................................................38
Outfall Design Requirements .............................................................................................................60
Prepare
action plan
.............................................................................................................................39
Environmental
Considerations...........................................................................................................60
Implementation
....................................................................................................................................40
Introduction ..........................................................................................................................................60
Introduction..........................................................................................................................................40
Outfall Design Requirements .............................................................................................................60
Carry
out work
.....................................................................................................................................40
Prevention
of septicity
........................................................................................................................60
Monitoring
performance
.....................................................................................................................41
Drains and sewers near water
abstraction areas .............................................................................61
Review
performance
requirements
and update plan.......................................................................41
Operational Considerations................................................................................................................61
9.6.1 Health
Introduction
..........................................................................................................................................61
7
and Safety
Principles ..............................................................................................................41
9.6.2 Separators ............................................................................................................................................61
8
................................................................................................................................42
9.6.3 Design
Design Principles
for self-cleansing
....................................................................................................................61
8.1
General
.................................................................................................................................................42
9.6.4 Access to drains and sewers .............................................................................................................62
8.2
Types of systems ................................................................................................................................42
10
Construction
Principles
......................................................................................................................63
8.3
Layout
and profile
...............................................................................................................................43
10.1
General..................................................................................................................................................63
8.4
Hydraulic
Design .................................................................................................................................44
10.2
Pipelines.................................................................................................................................................44
...............................................................................................................................................63
8.4.1
General
10.3
Ancillaries.............................................................................................................................................63
8.4.2
Foul
drains and sewers.......................................................................................................................44
8.4.3
Surface
water
drains
and sewers ......................................................................................................45
11
Operations
and
Maintenance..............................................................................................................64
8.4.4
Combined
drains
and
sewers ............................................................................................................47
11.1
Introduction ..........................................................................................................................................64
8.5
Environmental
Considerations
..........................................................................................................47
11.2
Objectives.............................................................................................................................................65
8.5.1
General
.................................................................................................................................................47
11.3
Data requirements ...............................................................................................................................65
8.5.2
Protection
of surface
receiving
waters .............................................................................................49
11.4
Investigation
and analysis
of operational
problems........................................................................66
8.5.3 Protection of Groundwater .................................................................................................................49
12
Performance
............................................................................................................................67
8.5.4
Prevention
oftesting
septicity
........................................................................................................................49
8.5.5 Combined sewer overflows and surface water treatment...............................................................50
13
Qualifications and Training ................................................................................................................67
8.5.6 Emergency overflows .........................................................................................................................50
14
Sources ofDesign.................................................................................................................................50
Additional Information.....................................................................................................68
8.6
Structural
8.6.1 Introduction..........................................................................................................................................50
Annex A (informative) Relevant EU Directives ...............................................................................................69
8.6.2 Structural design of pipelines ............................................................................................................51
A.1
Introduction ..........................................................................................................................................69
8.6.3 Structural design of other components ............................................................................................51
A.2
Relevant Directives..............................................................................................................................69
8.6.4 Materials selection ..............................................................................................................................51
8.7
...............................................................................................................52
Annex BOperational
(informative)Considerations
Sources of Additional
Information ............................................................................70
8.7.1
General
B.1
National.................................................................................................................................................52
Standards Bodies .................................................................................................................70
8.7.2
Separators
............................................................................................................................................52
B.2
Austria...................................................................................................................................................70
8.7.3
conditions
...................................................................................................................52
B.2.1 Self-cleansing
Regulatory Bodies
...............................................................................................................................70
8.7.4
to drains and sewers .............................................................................................................53
B.2.2 Access
Other organisations.............................................................................................................................70
B.3
Denmark................................................................................................................................................71
9
Detailed Design....................................................................................................................................53
B.3.1 Regulatory Bodies ...............................................................................................................................71
9.1
Introduction..........................................................................................................................................53
B.3.2 Other organisations.............................................................................................................................71
9.2
Layout and profile ...............................................................................................................................53
B.4
France ...................................................................................................................................................72
9.2.1 Introduction..........................................................................................................................................53
B.4.1 Regulatory Bodies ...............................................................................................................................72
9.2.2 Layout ...................................................................................................................................................53
B.4.2 Other organisations.............................................................................................................................72
9.2.3 Accessibility.........................................................................................................................................54
B.5
Germany ...............................................................................................................................................72
9.2.4 Depth.....................................................................................................................................................54
B.5.1 Regulatory Bodies ...............................................................................................................................72
9.2.5 Need for pumping................................................................................................................................55
B.5.2 Other organisations.............................................................................................................................73
9.2.6 Pumping Installations .........................................................................................................................55
B.6
Ireland ...................................................................................................................................................73
9.3
Preliminary Investigations..................................................................................................................56
B.7
Italy........................................................................................................................................................73
9.3.1 General .................................................................................................................................................56
B.7.1 Regulatory Bodies ...............................................................................................................................73
9.3.2 Topography..........................................................................................................................................56
B.7.2 Other organisations.............................................................................................................................73
9.3.3 Geotechnical Survey ...........................................................................................................................56
B.8
The Netherlands...................................................................................................................................74
9.3.4 Groundwater ........................................................................................................................................57
B.8.1 Regulatory Bodies ...............................................................................................................................74
9.3.5 Existing drainage services .................................................................................................................57
B.8.2 Other organisations.............................................................................................................................74
9.3.6 Other existing utility services ............................................................................................................57
B.9
Norway ..................................................................................................................................................75
9.3.7 Extraneous water.................................................................................................................................57
B.9.1 Regulatory Bodies ...............................................................................................................................75
9.4
Hydraulic Design .................................................................................................................................57
B.9.2 Other organisations.............................................................................................................................75
9.4.1 Introduction..........................................................................................................................................57
B.10
Portugal ................................................................................................................................................75
9.4.2 Foul drains and sewers.......................................................................................................................57
B.10.1 Regulatory Bodies ...............................................................................................................................75
9.4.3 Surface water drains and sewers ......................................................................................................58
B.10.2 Other organisations.............................................................................................................................76
4
3
BS EN 752:2008
EN 752:2008 (E)
BS EN 752:2008
EN 752:2008 (E)
9.4.4
B.11 Combined
Sweden .................................................................................................................................................76
drains and sewers.............................................................................................................58
9.4.5
B.11.1 Capacity
Regulatory
of Bodies...............................................................................................................................76
pipelines ...........................................................................................................................59
9.4.6
B.11.2 Sewers
Other organisations
with steep gradients
............................................................................................................................76
..............................................................................................................59
9.4.7
B.12
Outfall
Switzerland...........................................................................................................................................76
Design Requirements .............................................................................................................60
9.5
B.12.1 Environmental
Regulatory Bodies...............................................................................................................................76
Considerations...........................................................................................................60
9.5.1
B.12.2 Introduction
Other organisations
..........................................................................................................................................60
............................................................................................................................77
9.5.2
B.13 Outfall
United Kingdom...................................................................................................................................77
Design Requirements .............................................................................................................60
9.5.3
B.13.1 Prevention
Regulatory of
Bodies...............................................................................................................................77
septicity ........................................................................................................................60
9.5.4
B.13.2 Drains
Other organisations
and sewers near
............................................................................................................................79
water abstraction areas .............................................................................61
9.6
Operational Considerations................................................................................................................61
Annex C (normative) Operations and maintenance ......................................................................................80
9.6.1 Introduction ..........................................................................................................................................61
C.1
Introduction..........................................................................................................................................80
9.6.2 Separators ............................................................................................................................................61
C.2
Operations planning............................................................................................................................80
9.6.3 Design for self-cleansing ....................................................................................................................61
C.2.1 Inspection routines .............................................................................................................................80
9.6.4 Access to drains and sewers .............................................................................................................62
C.2.2 Operations procedures .......................................................................................................................80
10
C.2.3 Construction
Contingency Planning.........................................................................................................................80
Principles ......................................................................................................................63
10.1
C.3
General..................................................................................................................................................63
Pipelines ...............................................................................................................................................81
10.2
C.3.1 Pipelines
General .................................................................................................................................................81
...............................................................................................................................................63
10.3
C.3.2 Ancillaries.............................................................................................................................................63
Functional problems ...........................................................................................................................81
C.3.3 Structural problems ............................................................................................................................82
11
Operations and Maintenance..............................................................................................................64
C.4
Manholes and Inspection Chambers.................................................................................................83
11.1
Introduction ..........................................................................................................................................64
C.5
Combined sewer overflows................................................................................................................83
11.2
Objectives.............................................................................................................................................65
C.6
Detention tanks....................................................................................................................................84
11.3
Data requirements ...............................................................................................................................65
C.7
Separators, settling chambers and gullies .......................................................................................84
11.4
Investigation and analysis of operational problems........................................................................66
C.8
Pumping installations .........................................................................................................................85
C.9
Inverted siphons..................................................................................................................................85
12
Performance
testing ............................................................................................................................67
C.10
Pest control ..........................................................................................................................................86
13
Qualifications and Training ................................................................................................................67
C.11
Making connections to existing drains and sewers ........................................................................86
C.12 Sources
Control of
drains
and sewers ..............................................................................................87
14
ofdisused
Additional
Information.....................................................................................................68
C.13
Control of building over or adjacent to sewers................................................................................87
Annex A (informative) Relevant EU Directives ...............................................................................................69
Annex DIntroduction
(normative) ..........................................................................................................................................69
Health and Safety .........................................................................................................88
A.1
D.1
Safe systems
of work..........................................................................................................................88
A.2
Relevant
Directives..............................................................................................................................69
D.2
Training and supervision....................................................................................................................88
Annex
BHazardous
(informative)
Sources of Additional Information ............................................................................70
D.3
atmospheres.....................................................................................................................88
B.1
National
Standards
Bodies
D.3.1 Oxygen deficient and
toxic .................................................................................................................70
atmospheres .........................................................................................88
B.2
Austria...................................................................................................................................................70
D.3.2 Potentially explosive atmospheres ...................................................................................................88
B.2.1
Regulatory
Bodies
...............................................................................................................................70
D.4
Traffic control
......................................................................................................................................89
B.2.2
Other
organisations.............................................................................................................................70
D.5
Protective equipment and welfare facilities......................................................................................89
B.3
Denmark................................................................................................................................................71
D.6
Emergency procedures.......................................................................................................................89
B.3.1
Regulatory
Bodies ...............................................................................................................................71
D.7
Temporary works.................................................................................................................................89
B.3.2
Other
organisations.............................................................................................................................71
D.8
Excavation work ..................................................................................................................................89
B.4
France
...................................................................................................................................................72
D.9
Hazardous
materials ...........................................................................................................................90
B.4.1
Regulatory
Bodies
...............................................................................................................................72
D.10
Vaccinations
........................................................................................................................................90
B.4.2 Other organisations.............................................................................................................................72
Annex EGermany
(normative)
Hydraulic Design ..........................................................................................................91
B.5
...............................................................................................................................................72
E.1
General .................................................................................................................................................91
B.5.1
Regulatory
Bodies ...............................................................................................................................72
E.1.1 Other
Introduction..........................................................................................................................................91
B.5.2
organisations.............................................................................................................................73
E.1.2 Ireland
Selection
of Flow Simulation Method................................................................................................91
B.6
...................................................................................................................................................73
E.2
Hydraulic calculations ........................................................................................................................92
B.7
Italy........................................................................................................................................................73
E.2.1 Regulatory
Velocity equations...............................................................................................................................92
B.7.1
Bodies ...............................................................................................................................73
E.2.2 Other
The Saint
Venant equations ...............................................................................................................94
B.7.2
organisations.............................................................................................................................73
E.3
Methods
of calculating runoff from small development schemes .................................................96
B.8
The
Netherlands...................................................................................................................................74
E.4
Calculation Bodies
of foul wastewater
flows for drain systems .................................................................97
B.8.1
Regulatory
...............................................................................................................................74
E.5
Calculation
of foul wastewater flows for sewer system..................................................................97
B.8.2
Other
organisations.............................................................................................................................74
E.6
Combined
sewer overflows................................................................................................................98
B.9
Norway
..................................................................................................................................................75
B.9.1 Regulatory Bodies ...............................................................................................................................75
Annex F (normative) Pumping Installations...................................................................................................99
B.9.2 Other organisations.............................................................................................................................75
F.1
General .................................................................................................................................................99
B.10
Portugal ................................................................................................................................................75
F.2
Planning of pumping installations.....................................................................................................99
B.10.1 Regulatory Bodies ...............................................................................................................................75
F.2.1 Preliminary Considerations................................................................................................................99
B.10.2 Other organisations.............................................................................................................................76
4
5
BS EN 752:2008
EN 752:2008 (E)
BS EN 752:2008
EN 752:2008 (E)
B.11
F.2.2 Sweden
Planning..............................................................................................................................................100
.................................................................................................................................................76
B.11.1
F.3
Regulatory
Design of pumping
Bodies...............................................................................................................................76
stations .............................................................................................................101
B.11.2
F.3.1 Other
Layoutorganisations
.................................................................................................................................................101
............................................................................................................................76
B.12
F.3.2 Switzerland...........................................................................................................................................76
Wet well design ..................................................................................................................................102
B.12.1
F.3.3 Regulatory
External layout
Bodies...............................................................................................................................76
and access...............................................................................................................103
B.12.2
F.3.4 Other
Environmental
organisations
impact
............................................................................................................................77
.......................................................................................................................103
B.13
F.3.5 United
Structural
Kingdom...................................................................................................................................77
design ...............................................................................................................................103
B.13.1
F.3.6 Regulatory
Maintenance
Bodies...............................................................................................................................77
considerations ............................................................................................................103
B.13.2
F.4
Other
Designorganisations
of rising mains
............................................................................................................................79
......................................................................................................................104
F.4.1 Principal considerations ...................................................................................................................104
Annex C (normative) Operations and maintenance ......................................................................................80
F.4.2 Choice of route...................................................................................................................................104
C.1
Introduction..........................................................................................................................................80
F.4.3 Choice of diameter.............................................................................................................................104
C.2
Operations planning............................................................................................................................80
F.4.4 Pressures and external loads...........................................................................................................104
C.2.1 Inspection routines .............................................................................................................................80
F.4.5 Choice of materials............................................................................................................................105
C.2.2 Operations procedures .......................................................................................................................80
F.4.6 Thrust..................................................................................................................................................105
C.2.3 Contingency Planning.........................................................................................................................80
F.4.7 Discharge points................................................................................................................................105
C.3
Pipelines ...............................................................................................................................................81
F.4.8 Control of Septicity............................................................................................................................105
C.3.1 General .................................................................................................................................................81
F.4.9 Valve chambers..................................................................................................................................105
C.3.2 Functional problems ...........................................................................................................................81
F.5
Components and appliances............................................................................................................106
C.3.3 Structural problems ............................................................................................................................82
F.5.1 Pumps .................................................................................................................................................106
C.4
Manholes and Inspection Chambers.................................................................................................83
F.5.2 Prime Movers and Drives..................................................................................................................106
C.5
Combined sewer overflows................................................................................................................83
F.5.3 Valves..................................................................................................................................................107
C.6
Detention tanks....................................................................................................................................84
F.5.4 Controls and electrical equipment...................................................................................................107
C.7
Separators, settling chambers and gullies .......................................................................................84
F.5.5 Instrumentation..................................................................................................................................108
C.8
Pumping installations .........................................................................................................................85
F.5.6 Alarms.................................................................................................................................................108
C.9
Inverted siphons..................................................................................................................................85
F.6
Health and Safety...............................................................................................................................108
C.10
Pest control ..........................................................................................................................................86
C.11
Bibliography
Making
....................................................................................................................................................110
connections to existing drains and sewers ........................................................................86
C.12
Control of disused drains and sewers ..............................................................................................87
C.13
Control of building over or adjacent to sewers................................................................................87
Annex D (normative) Health and Safety .........................................................................................................88
D.1
Safe systems of work..........................................................................................................................88
D.2
Training and supervision....................................................................................................................88
D.3
Hazardous atmospheres.....................................................................................................................88
D.3.1 Oxygen deficient and toxic atmospheres .........................................................................................88
D.3.2 Potentially explosive atmospheres ...................................................................................................88
D.4
Traffic control ......................................................................................................................................89
D.5
Protective equipment and welfare facilities......................................................................................89
D.6
Emergency procedures.......................................................................................................................89
D.7
Temporary works.................................................................................................................................89
D.8
Excavation work ..................................................................................................................................89
D.9
Hazardous materials ...........................................................................................................................90
D.10
Vaccinations ........................................................................................................................................90
Annex E (normative) Hydraulic Design ..........................................................................................................91
E.1
General .................................................................................................................................................91
E.1.1 Introduction..........................................................................................................................................91
E.1.2 Selection of Flow Simulation Method................................................................................................91
E.2
Hydraulic calculations ........................................................................................................................92
E.2.1 Velocity equations...............................................................................................................................92
E.2.2 The Saint Venant equations ...............................................................................................................94
E.3
Methods of calculating runoff from small development schemes .................................................96
E.4
Calculation of foul wastewater flows for drain systems .................................................................97
E.5
Calculation of foul wastewater flows for sewer system..................................................................97
E.6
Combined sewer overflows................................................................................................................98
Annex F (normative) Pumping Installations...................................................................................................99
F.1
General .................................................................................................................................................99
F.2
Planning of pumping installations.....................................................................................................99
F.2.1 Preliminary Considerations................................................................................................................99
6
5
BS EN 752:2008
EN 752:2008 (E)
BS EN 752:2008
EN 752:2008 (E)
F.2.2 Planning..............................................................................................................................................100
F.3
Design of pumping stations .............................................................................................................101
F.3.1 Layout .................................................................................................................................................101
F.3.2 Wet well design ..................................................................................................................................102
F.3.3 External layout and access...............................................................................................................103
Foreword
F.3.4 Environmental impact .......................................................................................................................103
F.3.5 Structural design ...............................................................................................................................103
This document
(EN 752:2008)
has ............................................................................................................103
been prepared by Technical Committee CEN/TC 165 “Wastewater
F.3.6
Maintenance
considerations
Engineering”,
theofsecretariat
of which
is held by DIN.
F.4
Design
rising mains
......................................................................................................................104
F.4.1 Principal considerations ...................................................................................................................104
This European
shall be given the status of a national standard, either by publication of an identical
F.4.2
ChoiceStandard
of route...................................................................................................................................104
text or by
endorsement,
at the latest by July 2008, and conflicting national standards shall be withdrawn at the
F.4.3
Choice
of diameter.............................................................................................................................104
latest byPressures
July 2008. and external loads...........................................................................................................104
F.4.4
F.4.5 Choice of materials............................................................................................................................105
AttentionThrust..................................................................................................................................................105
is drawn to the possibility that some of the elements of this document may be the subject of patent
F.4.6
rights. CEN
[and/or points................................................................................................................................105
CENELEC] shall not be held responsible for identifying any or all such patent rights.
F.4.7
Discharge
F.4.8 Control of Septicity............................................................................................................................105
F.4.9
Valve chambers..................................................................................................................................105
This document
supersedes EN 752-1:1995, EN 752-2:1996, EN 752-3:1996, EN 752-4:1997, EN 752-5:1997,
F.5
Components
and appliances............................................................................................................106
EN 752-6:1998,
EN 752-7:1998.
F.5.1 Pumps .................................................................................................................................................106
F.5.2
Prime
Movers
and Drives..................................................................................................................106
According
to the
CEN/CENELEC
Internal Regulations, the national standards organizations of the following
F.5.3
countriesValves..................................................................................................................................................107
are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
F.5.4
Controls
andEstonia,
electrical
equipment...................................................................................................107
Republic,
Denmark,
Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
F.5.5
Instrumentation..................................................................................................................................108
Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
F.5.6
Sweden,Alarms.................................................................................................................................................108
Switzerland and the United Kingdom.
F.6
Health and Safety...............................................................................................................................108
Bibliography ....................................................................................................................................................110
6
7
BS EN 752:2008
EN 752:2008 (E)
Introduction
Drain and sewer systems are part of the overall wastewater system that provides a service to the community.
This can be briefly described as:

removal of wastewater from premises for public health and hygienic reasons;

prevention of flooding in urbanised areas;

protection of the environment.
The overall wastewater system has four successive functions:

Collection;

Transport;

Treatment;

Discharge.
Drain and sewer systems provide for the collection and transport of wastewater.
Historically, drain and sewer systems were installed because there was a need to remove the polluted water
to prevent diseases.
Traditionally, drain and sewer systems were constructed to collect and transport all types of wastewater
together irrespective of the initial source. This led to difficulties in handling the peak flows in times of heavy
rainfall and to the introduction of combined sewer overflows, which discharged polluted water to surface
receiving waters.
It was later recognised that separate systems, where foul wastewater was kept separate from runoff derived
from surface water, would be an improvement over such combined systems.
Although many drain and sewer systems started out as combined systems there are strong arguments for
considering the separation of foul wastewater and surface water. The pollutant effects are not the same and
the separation of effluents allows for the different treatment for each element of wastewater, providing more
environmentally friendly solutions.
This concept is included in the approach of integrated sewer management.
EN 752 provides a framework for the design, construction, rehabilitation, maintenance and operation of drain
and sewer systems outside buildings. This is illustrated in the upper part of the diagram below. EN 752 is
supported by more detailed standards for the investigation, design, construction, organisation and control of
drain and sewer systems such as those listed in the lower part of the diagram. To support these detailed
standards information will come from specifications produced by individual organisations for their own use.
Product standards should also take into account the functional requirements in EN 752 through EN 476,
EN 773, EN 1293, EN 13380 and EN 14457.
8
BS EN 752:2008
EN 752:2008 (E)
Figure 1 — Pyramid Diagram
9
BS EN 752:2008
EN 752:2008 (E)
1
Scope
This European Standard sets out the objectives for drain and sewer systems outside buildings. It specifies the
functional requirements for achieving these objectives and the principles for strategic and policy activities
relating to planning, design, installation, operation, maintenance and rehabilitation.
It is applicable to drain and sewer systems, which operate essentially under gravity, from the point where
wastewater leaves a building, roof drainage system, or paved area, to the point where it is discharged into a
wastewater treatment plant or receiving water.
Drains and sewers below buildings are included provided that they do not form part of the drainage system for
the building.
2
Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 476:1997, General requirements for components used in discharge pipes, drains and sewers for gravity
systems
EN 858-1, Separator systems for light liquids (e.g. oil and petrol) — Part 1: Principles of product design,
performance and testing, marking and quality control
EN 858-2, Separator systems for light liquids (e.g. oil and petrol) — Part 2: Selection of nominal size,
installation, operation and maintenance
EN 1295-1, Structural design of buried pipelines under various conditions of loading — Part 1: General
requirements
EN 1610, Construction and testing of drains and sewers
EN 1825-1, Grease separators — Part 1: Principles of design, performance and testing, marking and quality
control
EN 1825-2, Grease separators — Part 2: Selection of nominal size, installation, operation and maintenance
EN 1990, Eurocode — Basis of structural design
EN 1991-1-1, Eurocode 1 — Actions on structures — Part 1-1: General actions Densities — self-weight,
imposed loads for buildings
EN 1991-1-2, Eurocode 1 — Actions on structures — Part 1-2: General actions — Actions on structures
exposed to fire
EN 1991-1-3, Eurocode 1 — Actions on structures — Part 1-3: General actions — Snow loads
EN 1991-1-5, Eurocode 1 — Actions on structures — Part 1-5: General actions — Thermal actions
EN 1991-2, Eurocode 1 — Actions on structures — Part 2: Traffic loads on bridges
EN 1991-4, Eurocode 1 — Actions on structures — Part 4: Silos and tanks
10
BS EN 752:2008
EN 752:2008 (E)
EN 1992-1-1, Eurocode 2 — Design of concrete structures — Part 1-1: General rules and rules for buildings
EN 1992-1-2, Eurocode 2 — Design of concrete structures — Part 1-2: General rules - Structural fire design
EN 1992-3, Eurocode 2 — Design of concrete structures — Part 3: Liquid retaining and containment
structures
ENV 1993-1-1, Eurocode 3 — Design of steel structures — Part 1-1: General rules and rules for buildings
EN 1994-1-1, Eurocode 4 — Design of composite steel and concrete structures — Part 1-1: General rules and
rules for buildings
EN 1996-1-1, Eurocode 6: Design of masonry structures — Part 1-1: General rules for reinforced and
unreinforced masonry structures
EN 1997-1, Eurocode 7: Geotechnical design — Part 1: General rulesEN 1998-1, Eurocode 8: Design of
structures for earthquake resistance — Part 1: General rules, seismic actions and rules for buildings
EN 1998-3, Eurocode 8: Design of structures for earthquake resistance — Part 3: Assessment and retrofitting
of buildings
EN 1998-1, Eurocode 8: Design of structures for earthquake resistance — Part 1: General rules, seismic
actions and rules for buildings
EN 1999-1-1, Eurocode 9: Design of aluminium structures — Part 1-1: General structural rules
EN 12889, Trenchless construction and testing of drains and sewers
EN 13508-2, Condition of drain and sewer systems outside buildings — Part 2: Visual inspection coding
system
EN 14654-1, Management and control of cleaning operations in drains and sewers — Part 1: Sewer cleaning
3
Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
aerobic
dissolved oxygen is present
[EN 1085:2007, definition 4100]
3.2
aesthetic
<of pollution> aspects sensed by sight or smell, e.g. floating solids, oil films or bank-side litter
3.3
air valve
valve used to allow air to escape from or enter into a rising main
3.4
anaerobic
dissolved oxygen, nitrate, nitrite and sulfate is absent
[EN 1085:2007, definition 4120]
11
BS EN 752:2008
EN 752:2008 (E)
3.5
backdrop manhole
manhole with a connection, by means of a vertical pipe, at or just above invert, from a drain or sewer at a
higher level
3.6
backwater level
elevation of the surface of the wastewater predicted or occurring in a drain or sewer system due to the
hydraulic conditions downstream
3.7
biochemical oxygen demand (BOD)
concentration of dissolved oxygen consumed under specific conditions (t days at 20 °C with or without
nitrification inhibition) by the biological oxidation of organic and/or inorganic matter in water
[EN 1085:2007, definition 3110]
3.8
catchment area
area draining to a drain, sewer or watercourse
[EN 1085:2007, definition 1270]
3.9
cleaning ball
spherical device, having an indented surface, designed to be carried through a drain or sewer by the flow to
facilitate removal of sediments
3.10
confined space
space in which the ventilation is restricted to the extent that special safety precautions need to be taken
3.11
combined sewer overflow
device, on a combined system that relieves the system of excess flow
[EN 1085:2007, definition 2130]
3.12
combined system
drain and sewer system designed to carry both foul wastewater and surface water in the same pipeline(s)
[EN 1085:2007, definition 2110]
3.13
common trench
trench in which more than one pipe is located
3.14
dam board
removable plank or section placed across a sewer or drain to divert or hold back the flow
3.15
depression storage
precipitation retained in surface hollows that does not contribute to runoff
3.16
design life
notional lifetime of an asset used for the purposes of design
12
BS EN 752:2008
EN 752:2008 (E)
3.17
detention tank
tank or reservoir for the temporary storage of wastewater
[EN 1085:2007, definition 2240]
3.18
domestic wastewater
water discharged from kitchens, laundry rooms, lavatories, bathrooms, toilets and similar facilities
[EN 1085:2007, definition 2030]
3.19
drain
pipeline, usually underground, designed to carry wastewater from a source to a sewer
[EN 1085:2007, definition 2250]
3.20
drainage service
natural or artificial system for the draining of a catchment area
3.21
dry weather flow
flow not affected by rainfall or snow melt
[EN 1085:2007, definition 3050]
3.22
dry well
dry chamber forming part of a pumping station and containing pumping equipment, normally used in
conjunction with a wet well
3.23
duty point
rate of flow and the corresponding total head for which a pump is designed or selected
3.24
exfiltration
escape of wastewater from a drain or sewer system into surrounding ground
[EN 1085:2007, definition 2230]
3.25
extraneous water
unwanted flow in a drain or sewer system
3.26
explosion proof
protected from causing ignition of flammable gases
3.27
flooding
condition where wastewater and/or surface water escapes from or cannot enter a drain or sewer system and
either lies on the surface or enters buildings (see also surface flooding)
3.28
flow balancing
reduction in peak discharge by means of temporary storage of flow
13
BS EN 752:2008
EN 752:2008 (E)
3.29
flushing
use of a temporary substantially increased flow to facilitate removal of obstructions or sediments from drains
or sewers
3.30
gravity system
drain or sewer system where flow is caused by the force of gravity and where the pipeline is designed usually
to operate partially full
[EN1085:2007, definition 2260]
3.31
hydro-biological stress
detrimental impact on aquatic flora and fauna, caused by high flow velocity and scour
3.32
infiltration
⟨into the ground⟩ the movement of surface water or treated effluent into the ground
[EN 1085:2007, definition 2210]
3.33
infiltration
⟨into the drain or sewer system⟩ unwanted flow resulting from an ingress of groundwater into a drain or sewer
system (see Figure 2)
[EN 1085:2007, definition 2220]
3.34
inspection chamber
chamber with a removable cover constructed on a drain or sewer that permits the introduction of cleaning and
inspection equipment from surface level, but does not provide access for personnel
3.35
integrated sewer system management
co-ordinated management of the planning, design, construction, rehabilitation, operation and maintenance of
all drain and sewer systems in a catchment area taking into account all aspects of their performance
3.36
integrated urban drainage management
co-ordinated management of the planning, design, construction, rehabilitation, operation and maintenance of
all urban drainage systems in a catchment area taking into account all aspects of their performance
3.37
integrated water policies
co-ordinated policies for the management of all bodies of water within a river basin including urban drainage
systems within it
3.38
inverted siphon
length of gravity drain or sewer that is lower than upstream or downstream lengths to allow the pipeline to
pass below an obstacle, and which consequently operates under pressure
3.39
jetting
use of high-pressure water jetting equipment to facilitate removal of obstructions or sediments from drains or
sewers
14
BS EN 752:2008
EN 752:2008 (E)
3.40
maintenance
routine work undertaken to ensure the continuing performance of drain and sewer systems
3.41
manhole
chamber with a removable cover constructed on a drain or sewer to permit entry by personnel
3.42
outfall
structure or point from which wastewater is discharged to a wastewater treatment plant or receiving water
[EN 1085:2007, definition 1280]
3.43
operations
actions taken in the course of normal functioning of drain and sewer systems (e.g. monitoring and regulation
or diversion of wastewater)
3.44
pumping installation
pumping station together with any associated rising main(s)
3.45
pumping station
building, structures and equipment used to transfer wastewater through a rising main or otherwise to raise the
wastewater
3.46
rainfall intensity
depth of rain falling in unit time, or volume of rain falling in unit time per unit area
3.47
ramp manhole
manhole with a steeply inclined pipe or channel from a drain or sewer at a higher level
3.48
rain water
water arising from atmospheric precipitation, which has not yet collected matter from the surface (see
Figure 2)
[EN 1085:2007, definition 2060]
3.49
receiving water
any type of water body where water or wastewater is discharged
[EN 1085:2007, definition 1100]
3.50
rehabilitation
measures for restoring or upgrading the performance of existing drain and sewer systems
3.51
relevant authority
organisation with appropriate statutory powers of control
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3.52
renovation
work incorporating all or part of the original fabric of the drain or sewer by means of which its current
performance is improved
3.53
repair
rectification of local damage
3.54
replacement
construction of a new drain or sewer, on or off the line of an existing drain or sewer, the function of the new
drain or sewer incorporating that of the old
3.55
retention time
time during which wastewater is held within the pumping installation
3.56
rising main
pipe through which wastewater is pumped
[EN 1085:2007, definition 2170]
3.57
rodding
use of appropriate device on the end of flexible rods to facilitate removal of obstructions (or sediments) from
drains or sewers
3.58
rodding point
small diameter non-man access connection to a drain or sewer that facilitates cleaning or inspection
3.59
runoff
water from precipitation which flows off a surface to reach a drain, sewer or receiving water (see Figure 2)
3.60
runoff coefficient
factor dependent on the ground catchment, and by which the rain water quantity per unit of time must be
multiplied in order to indicate the flow expected to be carried to the drain or sewer system
3.61
self-cleansing
ability of the flow in a drain or sewer to carry away solid particles, which would otherwise be deposited in the
pipe
3.62
self-purifying capacity
ability of receiving waters to recover from pollution by natural processes
3.63
separate system
drain and sewer system, usually of two pipelines, one carrying foul wastewater and the other surface water
[EN 1085:2007, definition 2120]
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3.64
septic wastewater
anaerobic wastewater which usually contains hydrogen sulphide
[EN 1085:2007, definition 2020]
3.65
sewer
pipeline or other construction, usually underground, designed to carry wastewater from more than one source
[EN 1085:2007, definition 2270]
3.66
sewer system
network of pipelines and ancillary works which conveys wastewater from drains to a treatment plant or other
place of disposal
[EN 1085:2007, definition 2270]
3.67
structural condition
state of a drain or sewer in matters relating to the integrity of its fabric
3.68
sub-critical flow
state of flow when the water velocity is less than the velocity of the small surface wave with water levels
tending to be stable
3.69
super-critical flow
state of flow when the water velocity is greater than the velocity of the small surface wave with violent
fluctuations in water level being possible
3.70
surcharge
condition in which wastewater and/or surface water is held under pressure within a gravity drain or sewer
system, but does not escape to the surface to cause flooding
3.71
surface flooding
condition where wastewater and/or surface water escapes from, or cannot enter, a drain or sewer system and
either lies on the surface or enters buildings from the surface (see also flooding)
3.72
surface receiving water
receiving water body that is on the surface of the ground (e.g. river, lake or sea) (see Figure 2)
3.73
surface water
water from precipitation, which has not seeped into the ground and which is discharged to the drain or sewer
system directly from the ground or from exterior building surfaces (see Figure 2)
[EN 1085:2007, definition 2070]
3.74
time of concentration
time taken for runoff to travel from the hydraulically most distant point of the catchment area to a defined point
in the drain or sewer
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3.75
tank sewer
section of sewer which acts as a detention tank
3.76
trade effluent
wastewater discharge resulting from any industrial or commercial activity
[EN 1085:2007, definition 2040]
3.77
urban drainage system
systems used for the collection and transport of wastewater and other rain water runoff in an urban area
Key
1
Rain Water (see 3.48)
2
Runoff (see 3.59)
3
Surface Water (see 3.73)
4
Infiltration (see 3.32)
5
Surface Receiving Water (see 3.72)
Figure 2 — Terminology for flows derived from rain water
3.78
utility services
services provided to customers and industry such as gas, electricity, telephone, cable TV and water
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3.79
vortex manhole
circular manhole within which a large difference in level is accommodated by the wastewater entering
tangentially and descending helically
3.80
wastewater
water composed of any combination of water discharged from domestic, industrial or commercial premises,
surface run-off and accidentally any sewer infiltration water
[EN 1085:2007, definition 1010]
3.81
wastewater treatment plant
facility for the physical, biological and/or chemical treatment of wastewater
[EN 1085:2007, definition 4500]
3.82
wet well
chamber forming a part of a wastewater pumping station into which wastewater discharges prior to pumping. It
can include submersible pumping equipment and pipework
3.83
whole life cost
aggregate cost of a scheme over its design life, being the sum of the construction, operating and maintenance
costs all calculated at the same time base
3.84
winching
use of a bucket or other device pulled through a drain or sewer to facilitate removal of sediments (or
obstructions)
4
Objectives
4.1 General
The four objectives of drain and sewer systems are:

Public health and safety;

Occupational health and safety;

Environmental protection;

Sustainable development.
A number of European Union Directives (e.g. the Urban Wastewater Treatment Directive (91/271/EEC)) make
requirements for drain and sewer systems which relate to these objectives. For further information see Annex
A (informative).
Drain and sewer systems are part of the urban drainage system (see Figure 3). Urban drainage systems
comprise all infrastructures for the management of wastewater and rain water in the built environment. The
extent and role of the drain and sewer system within the urban drainage system will depend on local
circumstances for each system.
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Urban drainage systems are part of a wider system of water management (see Figure 3). The Water
Framework Directive (2000/60/EC) provides the basis for integrated management of the whole water
management system through the river basin management plan.
Integrated sewer system management includes a consideration of the interactions of the drain and sewer
system with the urban drainage system as a whole, and the wider water environment.
4.2 Public Health and Safety
Drain and Sewer systems are provided in order to:

prevent spread of disease by contact with faecal and other waterborne waste;

protect drinking water sources from contamination by waterborne waste;

carry runoff and surface water away while minimising hazards to the public.
Poorly designed, constructed or maintained systems can cause health or safety hazards to the public.
The objective is to design, construct, operate, maintain and rehabilitate the system in order to minimise the
health and safety risks associated with the conveyance of wastewater.
4.3 Occupational Health and Safety
All work associated with the installation, operation, maintenance and rehabilitation of drain and sewer systems
presents a range of occupational health and safety hazards.
The objective is to minimise the occupational health and safety risks likely to arise during installation,
operation, maintenance, and rehabilitation.
4.4 Environmental Protection
The objective is to design, construct, operate and maintain the system to minimise the impact on the
environment.
The impact of drain and sewer systems on the receiving waters shall meet the requirements of any national or
local regulations or the relevant authority. Other environmental requirements specified by any national or local
regulations or the relevant authority shall also be met.
4.5 Sustainable Development
The objective is to design, construct, operate, maintain and rehabilitate the system at the best environmental,
social and economical costs so that it:
a) uses materials that minimise the depletion of finite resources;
b) can be operated with the minimum practicable use of energy; and,
c) can be constructed, operated and, at the end of their life, decommissioned with the minimum practicable
impact on the environment.
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5
Requirements
5.1 Functional Requirements
5.1.1
Introduction
Functional requirements cover the drain and sewer systems, together with combined sewer overflows,
pumping installations and other components, including the effects of their discharges on receiving waters and
the receiving wastewater treatment plant. The requirements shall be considered in respect of the whole
system to ensure that additions or modifications to the system do not result in failure to meet the target
standards.
Requirements shall be established that, whilst taking into account sustainable development and whole life
costs including indirect costs (e.g. cost of social disruption), ensure that drain and sewer systems convey and
discharge their contents without causing unacceptable environmental nuisance, risk to public health, or risk to
personnel working therein.
Each functional requirement can relate to more than one objective. An indication of the relevance of each of
the functional requirements to achieving the objectives is shown in Table 1.
Table 1 — Relationship between objectives and functional requirements
Clause No
Public Health
and Safety
Occupational
Health and
Safety
Environmental
Protection
Sustainable
development
5.1.2 Protection from flooding
XXX
XX
XXX
–
5.1.3 Maintainability
XX
XXX
XX
XX
surface
XXX
X
XXX
XX
5.1.5 Protection of groundwater
XXX
–
XXX
XXX
5.1.6 Prevention of odours and
toxic, explosive and corrosive
gases
XXX
XXX
XXX
XXX
5.1.7 Prevention of noise and
vibration
XX
XXX
X
X
5.1.8
Sustainable
use
products and materials
of
–
–
XX
XXX
5.1.9 Sustainable use of energy
–
–
XX
XXX
5.1.10 Structural integrity and
design life
XXX
XXX
XXX
XXX
5.1.11 Maintaining the flow
XXX
–
XXX
X
5.1.12 Watertightness
XXX
X
XXX
XX
5.1.13 Not endangering adjacent
structures and utility services
XXX
XXX
X
XX
5.1.14 Inputs quality
XX
XXX
XXX
XX
5.1.4 Protection
receiving waters
NOTE
of
XXX is High;
X is Low and;
– is not related.
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5.1.2
Protection from flooding
Flooding from drains and sewers can have a major impact on the health of people affected. The economic
impact can be high and depends on the type of location flooded.
Flooding shall be limited to nationally or locally prescribed frequencies taking into account the:

health and safety effects of the flooding;

costs of the flooding;

extent to which any surface flooding can be controlled without causing damage;

whether surcharge is likely to lead to flooding of basements.
NOTE
In some jurisdictions it is the responsibility of the property owner to provide protection to prevent flooding of
basements due to surcharge.
The hydraulic capacity shall limit flooding to nationally or locally prescribed levels and frequencies taking into
account backwater levels. The hydraulic capacity shall allow for foreseeable increases in flow over the design
life of the system. The effects of flows discharged into downstream sewers or receiving waters shall be
considered. Further details are included in clause 8.
Where there are components in the system, which have a high risk of failure, measures should be taken to
avoid or minimise the risk of flooding in the event of failure of those components.
5.1.3
Maintainability
The system shall be planned, designed, constructed and rehabilitated to allow appropriate maintenance
activities to be carried out safely and without risks to the health of personnel.
Adequate access and working space shall be provided for maintenance purposes.
5.1.4
Protection of surface receiving waters
Surface receiving waters shall be protected from pollution within nationally or locally prescribed limits.
The impact of drain and sewer systems on the surface receiving waters shall meet the requirements of any
national or local regulations or the relevant authority. Other environmental requirements specified by any
national or local regulations or the relevant authority shall also be met.
The measures to achieve the standards required under Water Framework Directive (2000/60/EC) will be
summarised in the Water Framework River Basin Plan.
5.1.5
Protection of groundwater
Groundwater shall be protected from pollution within nationally or locally prescribed limits. The effect of the
drain and sewer system on the local recharge of aquifers shall be considered.
The impact of drain and sewer systems on the receiving groundwater shall meet the requirements of any
national or local regulations or the relevant authority. Other environmental requirements specified by any
national or local regulations or the relevant authority shall also be met.
The measures to achieve the standards required under Water Framework Directive will be summarised in the
Water Framework River Basin Plan.
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5.1.6
Prevention of odours and toxic, explosive and corrosive gases
Sewer systems shall be designed, constructed, maintained and operated to avoid odour nuisance, or toxic,
explosive or corrosive gases.
5.1.7
Prevention of noise and vibration
The system shall be designed, constructed, maintained and operated so that noise and vibration are
minimised.
5.1.8
Sustainable use of products and materials
Products, materials, and their construction methods shall be selected that minimise depletion of finite
resources having regard to the design life of the component and the potential for re-use or recycling, for
example minimising the volume of excavated material and the reuse of excavated material.
5.1.9
Sustainable use of energy
The design and operation of the drain and sewer system shall, so far as is practical, minimise the use of
energy over the life of the system.
5.1.10 Structural integrity and design life
Drains, sewers and other components shall be designed, constructed, maintained and operated to ensure
structural integrity over the design life.
5.1.11 Maintaining the flow
The system shall be designed, constructed, maintained and operated to reliably convey all design flows that
can legally be discharged into the system to the point of discharge, ensuring that the operation of the system
is safe, environmentally acceptable and economically efficient.
5.1.12 Watertightness
New drains, sewers and ancillary structures shall be watertight in accordance with the testing requirements of
EN 1610. Existing drains, sewers and ancillary structures shall be watertight in accordance with national or
local testing requirements.
5.1.13 Not endangering adjacent structures and utility services
The design, construction, maintenance and operation of drains and sewers shall not endanger existing
adjacent structures and utility services.
5.1.14 Inputs quality
The drain and sewer system can be designed to receive both domestic and non-domestic wastewater inputs.
The quality of the non-domestic inputs shall be controlled so that they do not compromise the integrity of the
fabric of the system or its function or constitute a danger for the environment. National or local regulations can
give requirements for inputs quality.
5.2 Determination of performance requirements for the drain and sewer system
In order to evaluate the performance of the system and to allow development of design standards,
measurable performance requirements shall be determined from each functional requirement. The process
for determining performance requirements is illustrated in Figure 4.
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For each functional requirement there can be legal requirements, public expectations and financial constraints
which will influence the performance requirements.
For each aspect of performance different levels could be required for example:

trigger levels which justify early upgrading action according to priority;

target levels to aim for in upgrading, which shall be equal to the requirements for new construction, but
which sometimes can only be achievable or necessary in the longer term.
Examples of performance requirements in use in different countries can be obtained from the organisations
listed in Annex B.
Performance requirements shall be reviewed periodically and updated if necessary. The performance
requirements for the system should be updated after major extension, maintenance or rehabilitation.
In principle the performance requirements for a rehabilitated system shall be the same as those for a new
system.
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Figure 3 — Drain and sewer systems in the river basin
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Figure 4 — Process for determining performance requirements
6
Integrated Sewer System Management
6.1 Introduction
Integrated sewer system management is the process of achieving an understanding of existing and proposed
drain and sewer systems, and using this information to develop strategies to ensure that the hydraulic,
environmental, structural and operational performance meets the specified performance requirements taking
into account future conditions and economic efficiency.
The integrated sewer system management process is illustrated in Figure 5.
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Figure 5 — Integrated Sewer System Management Process
The integrated sewer system management process has four principal activities.

Appropriate level of investigation of all aspects of the performance of the drain and sewers system;

Assessment of the performance by comparison with the performance requirements including identification
of the reasons for the performance failures;

Developing the plan of measures to be taken;

Implementation of the plan.
The need for further investigation can become apparent either during the performance assessment or the
development of the plan.
Integrated sewer system management forms the basis for the operation and rehabilitation of the drain and
sewer system. The information is regularly updated for the future management of the drain and sewer system.
The role of the drain and sewer system should be determined within the context of the whole river basin
catchment and the other elements of the urban drainage system. To determine this role account should be
taken of integrated water policies set by any national or local regulations or the relevant authority together with
any requirements of the integrated river basin management plan. Account should also be taken of any policies
resulting from integrated urban drainage management.
The boundary conditions should also be considered.
6.2 Investigation
6.2.1
Introduction
The investigation is the first stage in the Integrated Sewer System Management as described in 6.1 (see
Figure 5). The process for investigation is outlined in Figure 6.
Damaged, defective or hydraulically overloaded drains and sewers represent a potential hazard through
flooding and collapses, and through pollution of surface receiving waters, groundwater and soil. The problems
found in existing drain and sewer systems are frequently interrelated and upgrading works will often be
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designed to overcome a number of problems at the same time. The investigation and planning of rehabilitation
work should be carried out on complete catchment areas so that all problems and their causes can be
considered together. In large sewer systems it could be necessary to start by investigating appropriate parts of
the system. The procedures described in this Standard can be applied in any drain and sewer system, but
detailed application should take account of the age, location and type of system, the materials used in its
construction, together with functional and climatic factors.
6.2.2
Purpose of investigation
The investigation is carried out in order to make an assessment of the performance of the drain and sewer
system and its components. This can include:

investigation aimed at strategic planning;

investigation aimed at operational planning.
The purpose of the investigation influences the way in which it will be carried out (e.g. choice of method,
degree of detail, desired accuracy) and the way in which the results will be assessed.
The components of the drain and sewer system included in the investigation shall be those that are necessary
to fulfil the purpose of the investigation. Examples include; drains, surface water and foul sewers, combined
sewers, gravity sewers, pressure/vacuum sewers, manholes, inspection chambers and other access facilities,
pumping stations, rising mains, storage and retention tanks, combined sewer overflows, monitoring facilities,
control facilities, outfalls, gravel and sand traps, flushing facilities, ventilation, sedimentation tanks, light
liquid/grease separators. EN 13508-1 gives guidance on establishing the condition of drain and sewer
systems.
6.2.3
Review of performance information
An indication of the type of performance problems, if any, on existing systems is likely to be known through
reports of incidents such as sewer collapses, flooding or polluted watercourses and from previous
investigations. Records of past incidents and any other relevant information should be brought together and a
detailed review should be carried out to establish the scope of the investigations.
Examples are; records of flooding incidents, pipe blockage incidents, sewer collapse incidents, rising mains
failures, disease, injury or fatal incidents to operators, disease, injury or fatal incidents to members of the
public, sewer damage incidents, compliance with discharge consents into and out of the system, closed circuit
television (CCTV) survey and visual inspection data, wastewater related odour complaint incidents, hydraulic
performance analysis, performance of mechanical/electrical equipment, results of monitoring, performance
and condition of flow control structures, sewer surcharge incidents.
The relevant authorities will be the source of many of the records listed above. All appropriate records should
be retained.
Where large numbers of complete or partial catchments are in need of investigation, the existing information
collected may also be used to assign priorities to the investigation of the perceived problems in each
catchment (for example by comparing the cost of the investigation with the benefit that might be achieved).
These can then be used to draw up a comprehensive programme so that the catchments with the most
serious problems are investigated first.
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Figure 6 — Process for investigation
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6.2.4
Determine the scope of the investigation
Following the review of the current performance information it will be possible to decide whether to carry out
an investigation and whether the extent of the problems justifies an investigation of the entire catchment area.
The extent and detail of the subsequent investigation of the hydraulic, environmental, structural and
operational aspects shall be determined. Further guidance on the type of investigations can be found in
EN 13508-1.
6.2.5
Review existing information
The collection and review of all available relevant information about the sewer system shall be carried out and
is the basis from which all other activities are subsequently planned. This information should include historical
records. In addition to the performance information listed in 6.2.3, examples are:

inventory including:

location, dimensions, shape and type of material of all drains and sewers;

position depth and levels of manholes and the levels of connections to the manholes;

positions of connections to drains and sewers;

layout of ancillary structures such as combined sewer overflows, outfalls and pumping installations,
including details of any special plant (e.g. pumps or screens).

relevant permits and legal requirements;

previous operational, maintenance, structural and safety measures to overcome the problems;

nature and quantities of trade effluent;

previous inspections;

previous hydraulic calculations or hydraulic models;

previous assessments of environmental impact;

existing drain and sewer condition data;

receiving water quality and use;

groundwater levels and velocities;

ground conditions including infiltration capacity;

groundwater protection zones;

previous test information;

characterisation of wastewater;

information on proposed new development or redevelopment within the catchment area.
Some of this information can be available from as-constructed drawings.
This information should be assessed to determine what further information is required in order to carry out the
investigation.
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6.2.6
Inventory update
Where the inventory is incomplete it shall be updated so that a sufficient record of the sewer system is
available to carry out the investigation.
NOTE
The update of the other information is included in the hydraulic, environmental, structural and operational
investigations.
6.2.7
Hydraulic investigation
Testing and inspection procedures can be required in order to ensure an adequate evaluation of flows (wet
and dry weather, infiltration, flow through gaps in manhole tops (between the cover and frame), exfiltration and
wrong connections). Surveys can include precipitation and flow measurements, identification of wrong
connections and groundwater measurements.
In some cases it is not possible to understand the hydraulics of the system without using a hydraulic model.
This sewer flow simulation model should be based on an as-built report updated after onsite investigation of
the main works. However a model is not usually recommended where:

there are no known hydraulic problems (particularly where the sewer system takes only foul wastewater
flows); and,

there are no combined sewer overflows; and,

structural problems are to be solved using techniques which do not reduce the hydraulic capacity of the
sewer.
Information on the use of computer based sewer flow simulation programs is given in 8.4.3.
Calibration and/or verification of the models shall be carried out whenever sufficient information is available.
The procedures used depend on the sewer flow simulation program.
If suitable agreement is not obtained, the model input data should be checked and then the sewer records.
Having identified possible causes of error it will often be necessary to confirm these by site inspection and
then adjust the model accordingly. Data shall not be modified without justification based on an inspection of
the system.
6.2.8
Environmental investigation
The environmental impact will depend on the nature of the wastewater and its potential to escape from the
system. In particular the location of trade effluent sources and contaminated surface water sources shall be
identified and the nature, quality, quantity and the potential environmental hazards reviewed.
Where necessary, surveys shall be carried out to provide any data not available from records.
Investigations can be required to determine where leakage from drains and sewers is affecting groundwater
quality, giving priority to drains or sewers which pass through aquifer protection zones or where they carry
particularly hazardous substances.
The quality of surface receiving waters shall be ascertained to see whether they meet the requirements and if
not, whether the sewer system is a significant factor.
Consideration should be given to other environmental factors such as noise, odour, visual intrusion and
potential soil contamination.
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6.2.9
Structural investigation
It is important to ensure that investigation of the system is selective in order to avoid duplication of previous
work. The structural investigations may include either a complete survey of the drain and sewer system or a
more selective approach. Consideration should be given to the age and location of existing infrastructure,
geotechnical data including the pipe bedding and surround, and the vulnerability of existing buildings and
other utility services.
Wherever practicable the recording of the structural condition of drain and sewer systems should be carried
out by an indirect system (e.g. closed circuit television (CCTV) system) in order to avoid personnel entering
the system (see clause 7). Where it is not possible to obtain sufficient information from indirect inspection
then direct inspection (e.g. by walking through the pipeline) may be used. The drain and sewer system shall
be cleaned as necessary to make it possible to record and assess the actual condition. The nature and
quantity of any material removed can be relevant to the structural investigation. During the survey the system
shall be kept free from wastewater as far as necessary.
The condition of the system shall be observed and recorded as accurately and comprehensively as
practicable. A uniform coding system complying with the requirements of EN 13508-2 shall be used to ensure
that the results can be compared.
NOTE
EN 13508-2 gives requirements for the method of recording observations from inspections. It does not give
requirements as to which observations should be recorded.
The observations recorded shall include all those that could affect the structural integrity of the system.
Examples include:

unacceptable fissures;

deformation;

displaced joints;

defective connections;

roots, infiltration, settled deposits, attached deposits, other obstacles;

subsidence;

defects in manholes and inspection chambers;

mechanical damage or chemical attack.
Where appropriate, other qualitative and quantitative investigation techniques may be used. These include
sonar (for pipes that are filled with water) and ground probing radar or other geophysical techniques (e.g. for
detecting voids behind the wall of the sewer pipe) or mechanical techniques (e.g. internal jacking to measure
the stiffness of the side wall support). Investigation of the chemical composition of the groundwater and the
soil should be carried out where this could affect the structural integrity.
The results of the structural investigations can also be relevant to the assessments of the hydraulic
performance and environmental impact.
6.2.10 Operational Investigation
Existing operational procedures, inspection schedules and maintenance plans shall be identified and
documented.
The frequency and location of recorded operational incidents (e.g. blockages, pumping station failures, sewer
collapses etc.) shall be reviewed.
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The impact of operational problems on the hydraulic, environmental and structural performance of the system
should be determined from incident records.
The causes of significant recurrent operational incidents shall be investigated.
To deal with operational problems in the most cost effective way, it is necessary to investigate and understand
the causes. Further information can be found in 11.4.
6.3 Assessment
6.3.1
Introduction
The performance of the system shall be assessed against the performance requirements.
Figure 7 — Process for assessment
EN 13508-1 gives guidance on evaluating the condition of the drain and sewer systems.
6.3.2
Assessment of the hydraulic performance
The results of the hydraulic surveys and/or the verified flow simulation model shall be used to assess the
hydraulic performance of the system for a range of rainfall conditions related to the performance requirements
(see 8.4.3).
6.3.3
Assessment of environmental impact
The results of the investigations shall be considered together with information on the frequency, duration and
volume of discharges to receiving waters, determined using a verified flow simulation model (see 6.2.7) where
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this is available or from site measurements. This information shall then be used to assess the environmental
impact (including impact on soil and groundwater) of the drain and sewer system (see 8.5).
The results of the structural investigation (see 6.2.9), the trade effluent survey and other relevant
investigations shall be examined to identify:

sources of hazardous effluents;

exceedence of permissible concentrations and discharges;

other deviations from permits.
6.3.4
Assess structural condition
Once the system has been inspected, the next stage is to examine the results to identify those areas requiring
action. A number of methods have been developed to assist in this process. Details of these can be obtained
from the organisations listed in Annex B.
6.3.5
Assess operational performance
The operational performance of the system as measured by the number of operational incidents or failures
should be assessed.
6.3.6
Compare with performance requirements
The results of the assessment of the hydraulic, environmental, structural and operational performance should
be brought together so that the overall performance of the system and its components can be compared to the
performance requirements (see 5.2).
Performance indicators are one method of comparing the overall performance of a system with performance
requirements. Any performance indicators used should be:

clearly defined, concise and unambiguous;

verifiable;

simple and easy to use.
6.3.7
Identify unacceptable impacts
Details of those parts of the system where the hydraulic, environmental, structural or operational performance
of the system or its components does not meet the performance requirements should be recorded.
6.3.8
Identify causes of performance deficiencies
Based upon the results of the hydraulic, environmental, structural and operational investigations, the causes
of performance deficiencies shall be determined. The relative impact of each cause should be assessed in
order to develop appropriate solutions and to set the priority for action.
6.4 Developing the Plan
6.4.1
Introduction
The process of producing the plan to fulfil the performance requirements is outlined in Figure 8.
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6.4.2
6.4.2.1
Develop integrated solutions
Introduction
Integrated solutions shall be developed that fulfil the performance requirements, taking into account future
conditions.
Figure 8 — Process for developing the plan
6.4.2.2
Hydraulic solutions
Hydraulic options include:
a) Maximise use of existing flow capacity by:

removal of constrictions;

cleansing.
b) Source control – Reducing the hydraulic input to the sewer system by:
c)

diversion of surface water flows to infiltration drainage systems or pervious areas;

use of porous pavements;

diversion of flows to another system;

reduction of infiltration and inflow of extraneous water.
Attenuate peak flows by:

mobilisation of existing storage potential within the system (strategically placed flow controls);

mobilisation of surface storage (including storage within the property boundary);

provision of additional storage (tank sewer or detention tank).
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d)
Increase sewer system flow capacity by:

replacement with larger pipe;

construction of additional pipeline;

renovation of the existing drain or sewer.
6.4.2.3
Environmental solutions
Environmental options include:
a) Reduce pollutant inputs to system by:
b)

sediment basins and grit separators;

use of vegetation to absorb pollutants from runoff before entering the system;

controlling inputs (e.g. trade effluents).
Decrease planned pollutant discharges to receiving waters by:

increase of flows to treatment (see hydraulic solutions above);

treatment of surface water discharges (e.g. by separators, retention ponds etc.)

improve solids retention and hydraulic performance of combined sewer overflows;

real time control.
c)
Decrease impact by relocation of points of discharge.
d)
Reduce exfiltration by rehabilitation measures such as:
36

repair techniques (e.g. sealing leaks);

renovation techniques (e.g. provision of watertight lining);

replacement of pipeline using open-cut or trench-less techniques.
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Figure 9 — Decision process for selection of structural solutions
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6.4.2.4
Structural solutions
Structural options include:
a) Protect fabric of sewer by provision of appropriate linings or internal coatings.
b)
Rehabilitate fabric of sewer by:

repair;

renovation;

replacement.
The decision process necessary to select the appropriate structural solution is given in Figure 9.
6.4.2.5
Operational solutions
In some cases an operational solution can be appropriate. Examples of possible operational solutions
include:

planned inspection and cleaning of a drain or sewer (see EN 14654-1);

increased frequency of maintenance of pumps or pumping stations.
6.4.3
Assess Solutions
Solutions shall be assessed and the optimal solution selected having regard to the basic performance
requirements (see clause 5) and factors such as:
a) Safety in construction and operation - The minimisation of risks to health and safety during
construction and subsequent operation of the system.
b)
Social disruption - The disruption to local residents and other members of the public due to traffic delays,
dust, noise and other social factors shall be considered.
c)
Sustainable use of resources - The use of energy and other finite resources in the construction and
operation of the system shall be taken into account. The ability to recycle materials used in the upgrading
works and any waste produced shall be considered.
d) Phasing of the works - The possibility of integrating the solution into a staged programme of works shall
be considered. This shall take into account the priorities of the works and the benefits in terms of
improved performance associated with each identified phase of the works, and the cost savings
associated with deferral of the later stages.
e)
Relationship to other infrastructure works - The benefits of phasing the works with other infrastructure
works shall be considered.
f)
Capacity and resource constraints - Account should be taken of the resource constraints (e.g.
personnel, supply chain and financial) in the selection and phasing of the options.
g)
Future maintenance liabilities - The cost of future maintenance works and other operational costs of the
system should be taken into account. The environmental impact of disposal of maintenance residues (see
8.5.1) shall also be considered.
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h)
Economic appraisal - The costs and benefits shall be considered to determine whether the additional
benefits of one solution over another, for example increased asset life, are justified.
i)
Whole life cost - The whole life cost of the solutions including temporary works, diversion of other utility
services and all design, investigation and operational costs shall be taken into account as well as the
indirect costs (e.g. cost of social disruption).
6.4.4
Prepare action plan
The selected integrated solution shall be documented to give a single plan for the drain and sewer system.
The documentation should include:

detailed objectives;

legal requirements and permits, including any timescales for improvement;

performance criteria;

priorities;

proposed works including costs and phasing;

relationship to other construction or planned development;

consequences for operations and maintenance.
Four types of plan can be prepared:
a) New development – Information on drainage of new developments proposed. Where significant new
development or redevelopment is proposed in the catchment, a plan should be produced showing:
1)
whether the foul and surface water from the new development should be drained by extension to
an existing drain or sewer system or by an independent system or, for surface water, by an infiltration
system;
2)
if the system is to be an extension of an existing system, the upgrading works to the existing
system to accommodate the additional flows should be described in the rehabilitation plan for that
system;
3)
b)
c)
outline of the main sewer systems to serve the development.
Rehabilitation plan – Information on proposed rehabilitation works. The options to be considered will fall
into one or more of the four categories: Hydraulic, Environmental, Structural and Operational performance.
The works necessary to upgrade an existing drain and sewer system to meet the performance
requirements should be incorporated into a rehabilitation plan. This should include:
1)
Details of the necessary upgrading works;
2)
Other options for upgrading the system;
3)
Any anticipated phasing of the work;
4)
Whether any of the items are conditional on any planned developments.
Operational plan – Inspection schedules, operational procedures and contingency plans. The operations
plan shall indicate the approach to be taken in a particular drain and sewer system. The plan shall
include:
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1)
inspection routines (see C.2.1);
2)
procedures used in the operation of the elements of the system (see C.2.2);
3)
contingency and emergency plans (see C.2.3).
d) Maintenance plan – Details of maintenance policies and schedules for each component of the system.
The maintenance plan shall include:
1)
2)
type of maintenance strategy to be used in each component of the system and the monitoring
requirements and frequencies. The strategies for maintaining drain and sewer systems are planned
or reactive maintenance, or a combination of both.
i)
Planned maintenance includes a programme of work to remedy the defects and problems
identified during inspection. It is particularly required to reduce the incidence of failure where the
consequences are severe.
ii)
Reactive (or crisis) maintenance involves responding to failures and problems as they are
identified. It is appropriate for those parts of the system that can function with little or no
maintenance.
risk assessment, taking into account the probability of failures and their consequences.
6.5 Implementation
6.5.1
Introduction
Figure 10 — Process for implementation
6.5.2
Carry out work
Where it is necessary to extend, reduce or rehabilitate the drain or sewer system these works should be
designed in accordance with clause 8 and clause 9 and constructed in accordance with clause 10.
The operations and maintenance plans should be implemented in accordance with clause 11.
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6.5.3
Monitoring performance
It is important to monitor the effectiveness of solutions and to update the plan, including the records
(inventory) and the hydraulic model (see clause 12).
6.5.4
Review performance requirements and update plan
The performance requirements should be reviewed periodically and the whole planning process repeated so
that all the plans remain up to date.
7
Health and Safety Principles
The fundamental strategy for occupational health and safety is laid down in the Framework Directive 89/391.
This requires employers to avoid risks to health and safety, to assess the risks which cannot be avoided and
to use the results of that assessment to mitigate the residual risks through combating these risks at source in
preference to the application of protective measures and to ensure that preference is given to collective
protective measures over those protecting the individual only. These are the principles of prevention. The
directive also requires that employees are appropriately instructed in the risks to their health and safety.
The Temporary or Mobile Construction Sites Directive 92/57 sets out requirements relating both to the design
and construction aspects of a project. With regard to design, Directive 92/57 requires that due account is
taken of the principles of prevention set out in the Framework Directive 89/391, in the design and preparation
stages of the project, that specific documentation regarding heath and safety risk is drawn up and made
available to parties to the project and that workers are consulted over and informed of the risks to their health
and safety. Annex IV of Directive 92/57 sets out a range of specific health, safety and welfare requirements
relating to work practices and to indoor and outdoor workplaces on site.
Accordingly drain and sewer systems shall be designed, constructed and operated so that the occupational
health and safety risks to personnel undertaking work associated with the drain and sewer system are
minimised. In addition welfare facilities shall be provided where appropriate.
Those who are responsible for work in drains and sewers, including the operator of the drain or sewer system
shall ensure that the work does not present a risk to the health or safety of any person carrying out the work or
any person who can be affected by their actions.
In addition it is the responsibility of employers to:

provide safe systems of work including arrangements for safe access to and egress from the sewer
system, and sufficient working space while in the sewer system;

ensure that their employees are properly instructed, trained and supervised in the work being carried out
and in the safe systems of work in use.
National or local regulations or the relevant authority can lay down requirements regarding the health, safety
and welfare of the public and/or personnel. They can include more requirements than indicated in this
standard.
The employer should define all tasks, competences and the ensuing responsibilities relating to the health and
safety activities. Furthermore, the employer should provide a well-structured documentation of its hierarchy
and organization of workflow [see EN ISO 9000 (all parts)]. Managers and supervisors responsible for safety
should check all relevant regulations for their proper application. If they detect flaws in the hierarchical and
workflow organization and/or the documented regulations, they should initiate immediate remedial action.
Further information on Health and Safety is found in Annex D.
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8
Design Principles
8.1 General
The basis of the design stage should be the action plan (see clause 6). Design is the process of defining the
project in sufficient detail so that instructions can be given to others for the system to be constructed or
maintained.
The design process includes the following stages:

conception;

preliminary topographical, geotechnical and other investigations (see 9.3);

preliminary calculations to check the feasibility of the proposed approach;

refinement of the general concept;

more detailed calculations;

production of detailed drawings or specifications.
The design process is typically iterative.
Designers should take into account the practicability of safely constructing, operating and maintaining the
system (see clause 7).
The design shall fulfil the objectives (see clause 4) and meet the functional requirements (see clause 5) and
the action plan (see clause 6). Specific requirements shall be considered in case of rehabilitation.
Together with the functional requirements (see clause 5) the financial and economic aspects of the various
options shall also be considered before reaching a decision as to the preferred solution. The above matters
shall be considered in terms of their implications on the whole life cost.
8.2 Types of systems
There are two types of wastewater to be collected and transported by the system; foul wastewater and surface
water. Two options are available as follows:

Combined system – where both types of wastewater are mixed;

Separate system – where each type of wastewater is collected and transported in a dedicated sewer
(surface water in a surface water sewer and foul wastewater in a foul sewer).
Variants of these basic systems are also possible.
The selection of a system will mainly depend upon:

national or local water management policies;

type of system which presently exists and how it is expected to evolve;

possible future changes in the catchment;

capacity and quality of receiving waters;

nature of influents to the system;
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
need for prior treatment;

topography;

ground characteristics;

treatment plant;

economic considerations;

other local conditions.
Adopting an integrated approach towards surface water drainage benefits both the quality and quantity
impacts on receiving waters. Where a new system is being proposed, surface water should be kept separate
from other wastewater. The discharge of surface water should be in accordance with the following hierarchy.
a)
To an adequate infiltration drainage system.
b)
Directly to a surface receiving water.
c)
To a drain or sewer system.
Storage should be provided to limit the peak discharges to acceptable flow rates.
National or local regulations or the relevant authority can specify the type of system to be used.
Permissible influents to the system are:

Domestic wastewater.

Authorised trade effluents. (In some cases pre-treatment of such trade effluents will be necessary before
discharge to the system is permitted in order to achieve the quality required by national or local
regulations or the relevant authority).

Surface water and, where exceptionally permitted, groundwater.
The nature of the expected influents shall be assessed.
The design shall take into account the conveyance of wastewater, including trade effluents, which will neither
damage the system and/or the wastewater treatment plant, nor impair their operation.
8.3 Layout and profile
The design of the system shall ensure that the layout and profile meets all relevant functional requirements
including:

Maintainability (see 5.1.3);

Protection of occupational health and safety (see 4.3);

Not endangering adjacent structures and utility services (see 5.1.13).
The layout and profile will be influenced by topography, the character of developments served, existing and
future flows from the catchment, the suitability of receiving waters or receiving wastewater treatment plant and
the adequacy of any existing system to accept the design flow.
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Economical design is usually achieved when drains and sewers follow the natural falls of the ground. Where
practicable they should be laid at such gradients as will prevent excessive accumulation of solid matter in the
invert. The route shall be selected so as not to impair the stability of structures.
Access chambers should be sited in locations where they can be reached by operator personnel and
equipment. Access should also be provided for excavation to repair a sewer, if this were to be necessary.
Circumstances can make the pumping of wastewater either necessary or advisable and should be considered
alongside the long-term energy commitments and the whole life costs involved. Detailed design of pumping
installations is considered in 9.2.6.
Positive and negative pressure systems are relatively independent of gradient and the depth of cover. In
certain circumstances they are alternatives to, or can form part of, systems operating essentially under gravity.
Long-term energy commitments and whole life costs including maintenance shall be considered for each
option. Positive pressure systems should be designed in accordance with EN 1671. Vacuum sewer systems
should be designed in accordance with EN 1091.
Where an appropriate sewer is not available and cannot immediately be provided, provision for local treatment
of wastewater shall be provided.
The levels of the receiving waters at the outfalls shall be taken into account in the planning of the sewer
system.
Detailed design of layout and profile is described in 9.2.
8.4 Hydraulic Design
8.4.1
General
The Hydraulic design of the system shall ensure that the design meets all relevant functional requirements
including:

Protection from flooding (see 5.1.2);

Maintainability (see 5.1.3);

Maintaining the flow (see 5.1.11).
8.4.2
Foul drains and sewers
The design flows for drains and sewers comprise:

Domestic wastewater flows;

Authorised trade effluent flows.
Extraneous water flows may be included in the calculation where these flows cannot be avoided.
Design flows should be calculated in accordance with 9.4.2.
The hydraulic capacity of the pipelines shall be calculated in accordance with Annex E. Surcharging is
undesirable in foul gravity drain and sewer systems. Foul drains and sewers should therefore be designed to
run at less than pipe full conditions.
Rising mains shall be designed to carry the required design flows in self-cleansing conditions without using
excessive energy (see Annex F). The retention time should also be limited so that septicity does not occur
(see 9.5.3).
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Detailed design of the hydraulic design of foul drains and sewers is described in 9.4.2.
8.4.3
8.4.3.1
Surface water drains and sewers
General
Surface water drains and sewers collect and transport runoff generated within a catchment area during rainfall,
for safe discharge into a receiving water or treatment plant. The magnitude of peak flows depends on the
intensity and duration of rainfall, the size and configuration of impermeable areas and measures taken to
reduce surface water. The topography, soil type and its permeability have also to be considered when
estimating the flows emanating from other areas.
Surface water drains and sewers are dimensioned in order to limit flooding. It is usually impracticable to avoid
flooding from very severe storms. A balance therefore has to be drawn between cost and the political choice
of the level of protection provided.
The level of protection should be based on a risk assessment of the impact of flooding to persons and
property. The level of protection should be specified in performance criteria for flooding frequencies or design
storm events used in calculation. The design criteria shall be based on the performance criteria.
The hydraulic capacity of surface water drains and sewers shall limit surcharge to nationally or locally
prescribed levels and frequencies taking into account backwater levels.
Surface water drains and sewers shall be designed so that the effect of any flooding caused by storms in
excess of the nationally or locally prescribed flooding frequencies causes the minimum of impact to persons
and property.
Storage should be provided (e.g. by use of detention tanks and ponds) to minimise the hydraulic impact on
receiving waters.
Other techniques can be used to reduce the runoff entering the drain and sewer system either in addition to or
as a substitute to the use of drains and sewers. These techniques are based on one or more of the following
principles:

infiltration systems;

minimising the area of impermeable surfaces connected to the drain and sewer system;

time lag and attenuation of the flow.
In setting hydraulic design performance criteria for surface water sewers, allowance shall be made for the
design methods that are likely to be used. In all cases the scale of the consequences of flooding should be
taken into account.
For surface water drains and sewers, design flows for the surface water pipelines will be runoff. No allowance
shall be made for any other wastewater component.
8.4.3.2
Surface water inlets
Surface water inlets shall be designed in order to ensure an adequate transfer of runoff from impermeable
areas into the surface water drains and sewers.
8.4.3.3
Design criteria
Design criteria shall take into account any changes in flows expected over the design life of the drain or sewer
system if these changes are not otherwise taken into account in the design. The potential effects of climate
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change should be considered. This is to ensure that the sewer continues to meet the performance criteria over
the design life of the system.
The frequency of an event may be expressed either as a return period or a probability of occurrence in any
one-year period.
Surcharge frequencies and depths in surface water drains and sewers shall be limited to any nationally or
locally prescribed values having regard to:

Whether there are any connected basements not protected by anti-flooding valves, effluent lifting stations
or pumping stations;

Whether the surcharge is likely to lead to flooding of basements.
Design flooding frequencies should be set in order to manage the risk of flooding, having regard to both the
frequency and consequences of flooding.
National or local regulations or the relevant authority can specify design storm frequencies or design flooding
frequencies or both. Different design criteria may be set for combined and separate systems.
The designer shall assess risk of flooding in events that exceed the design flood frequency, taking into
account both the consequences of the flooding and the frequency. Flow routes for excess flows should be
investigated to determine the consequences and where possible, the design should be changed to minimise
the impact. Where the risk of flooding cannot be reduced by these means the design frequency should be
decreased.
The nature of design criteria will depend on the type of design methods used.
a) Design Criteria for use with Simple design methods
In simple design methods the pipes are usually designed to run full, without surcharge, for relatively frequent
storms in the knowledge that this provides protection against flooding from much larger storms.
In the absence of any design criteria specified in national or local regulations or by the relevant authority the
"design storm frequency" for no surcharge criteria in Table 2 should be used for small schemes.
These approaches should be applied when an existing system is being considered for upgrading.
Both the storm frequency and the flood frequency may be expressed as a return period, which is the average
period in years between events, or a probability that an event will occur in any year.
Table 2 — Recommended design frequencies for use with simple design methods
Location
Return period
(1 in “n” years)
Probability of
exceeding
in any 1 year
Rural areas.
1 in 1
100 %
Residential areas.
1 in 2
50 %
City centres/industrial/commercial areas.
1 in 5
20 %
Underground railway/underpasses.
1 in 10
10 %
a
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Design storm frequency a
For those design storms no surcharge shall occur.
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b) More complex methods
For larger developments and for schemes particularly where risks to public health or the environment are
significant, time-varying design rainfall and computer based flow simulation models shall be used. Any model
used shall be chosen in cooperation with the relevant authority. For any application it is necessary to select a
method where the appropriate balance between cost complexity and required accuracy is achieved. Guidance
on when they should be used and the type of method to select is given in normative Annex E.
In these cases design should be undertaken to limit frequency of surcharge following which the design should
be checked to ensure that the design meets the design flood frequency criteria at specific sensitive locations.
These design checks are particularly important on steeply sloping catchment areas.
In the absence of any design criteria specified in national or local regulations or by the relevant authority the
design flooding frequency values given in Table 3 may be used.
Table 3 — Recommended design frequencies for use with complex design methods
Location
Design flooding frequency
Return period
(1 in “n” years)
Probability of
exceedingin any
1 year
Rural areas.
1 in 10
10 %
Residential areas.
1 in 20
5%
City centres/industrial/commercial areas.
1 in 30
3%
Underground railway/underpasses.
1 in 50
2%
Detailed design of the hydraulic design of surface water drains and sewers is described in 9.4.3.
8.4.4
Combined drains and sewers
The hydraulic design of combined drain and sewers shall be undertaken in the same way as surface water
drains and sewers with the design flows increased to include the dry weather flow. Since the dry weather flow
is generally only a small proportion of the capacity of the sewer, less allowance is necessary for the peak dry
weather flow rate.
Detailed design of the hydraulic design of combined drains and sewers is described in 9.4.4.
For combined drains and sewers, the design flowrate is made up of runoff, which is by far the predominant
component, plus an allowance for foul wastewater flows. The runoff component should therefore be estimated
using the methods outlined in 9.4.3. The foul wastewater component is estimated as described in 9.4.2. As the
foul wastewater flows are usually considerably lower than the design flowrates, particular consideration should
be given to self-cleansing velocities during dry weather conditions.
8.5 Environmental Considerations
8.5.1
General
The environmental design of the system shall ensure that the design meets all relevant functional
requirements including:

Protection of surface receiving waters (see 5.1.4);
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
Protection groundwater (see 5.1.5);

Prevention of odours, toxic, explosive and corrosive gases (see 5.1.6);

Prevention of noise and vibration (see 5.1.7);

Minimising the use of finite resources (see 5.1.8 and 5.1.9).
Control of the sources of pollution from drain and sewer systems shall be considered as it can limit the
environmental impact to levels acceptable to the relevant authority.
Consideration of impacts shall pay due regard both to short-term effects and to cumulative long-term effects.
Short-term effects can include fall in the concentration of dissolved oxygen, acute toxicity and hydro-biological
stress. Cumulative long-term effects can include the build up, in aquatic biota and sediments, of persistent
pollutants such as heavy metals and certain organic compounds.
Sources of environmental impact include:

outfalls;

combined sewer overflows;

emergency overflows, for example from pumping installations or detention tanks;

exfiltration to groundwater;

infiltration of groundwater;

untreatable non-domestic wastewater;

disposal of residues produced during sewer cleaning (see EN 14654-1).
Any untreatable non-domestic wastewater can have an impact when subsequently discharged from a
combined sewer overflow or the wastewater treatment plant.
Infiltration can also affect the frequency and volume of discharges from combined sewer overflows and the
quality of discharges from wastewater treatment plants.
Consideration shall be given to the risk of spills of noxious substances within the catchment area, particularly
on surface water systems. Where there is significant risk of spillage or discharge of significant quantities of fire
fighting water containing harmful substances, appropriate measures shall be taken to avoid entry into or exit
from the sewer system of these substances by, for example, the provision of separators (see 8.7.2) or
retention tanks.
Pipelines shall be designed to avoid leakage that might cause pollution of groundwater.
To minimise odour nuisance gravity drains and sewers shall be sufficiently ventilated to atmosphere by
allowing a free passage of air through the system. In very cold areas special precautions can be required.
Disused drains and sewers shall be removed or, where this is impracticable, they shall be filled with suitable
material to prevent for example, structural deterioration, unauthorised use, ingress of groundwater and
infestation by rodents.
Care should be taken in the design of systems to minimise the accumulation of deposits as residues from
sewer cleaning activities can cause pollution.
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8.5.2
Protection of surface receiving waters
The quality, quantity and frequency of any discharge to receiving water from any sewer including a surface
water sewer, combined sewer overflow, pumping installation or treatment works shall meet the requirements
of any national or local regulations or the relevant authority. Design shall be such that the receiving water will
be protected against overloading of its self-purifying capacity. It shall take account of physical, chemical,
biochemical, bacteriological, aesthetic and any other relevant considerations.
There are two approaches to the control of pollution from drain and sewer systems:

uniform emission limits can be set by national or local regulations or the relevant authority for general use
with each of the different types of discharge;

site-specific emission limits can be set by any national or local regulations or the relevant authority for
individual points of discharge, to satisfy requirements for the quality and characteristics of the receiving
water taking into account any emission limits and the specific needs of the receiving water.
In many cases a combination of the two approaches should be considered.
Uniform emission limits are generally set in relation to what is technically feasible for the different types of
discharge. They form a baseline standard prior to the determination of site-specific limits which will not put the
self-purifying capacity of the receiving water at risk. They are unlikely to be applicable where discharge is to
sensitive waters such as recreational areas, sources for water supply or lakes. Generally in such cases, more
stringent site-specific emission limits will be necessary to satisfy the receiving water quality requirements.
The site-specific emission limit approach is sensitive not just to the effects of an individual discharge, but also
to the combined effects of the whole range of discharges to receiving waters. These discharges, including
those from industry, treatment works and non-point sources can demand an integrated approach to the
identification of solutions.
The relevant authority for environmental regulation can classify receiving waters according to current or
projected uses or interests, for example:

abstraction for potable supply;

fishery;

bathing or other water contact activities;

special ecosystem.
The emission limits can then be set by any national or local regulations or the relevant authority using, where
appropriate, water quality simulation models.
8.5.3
Protection of Groundwater
In order to protect groundwater, the national or local regulations or the relevant authority can require stringent
performance and testing in high-risk areas such as drinking water abstraction or aquifer protection zones and
areas with high groundwater levels. In such areas a number of zones with different levels of protection can be
specified by any national or local regulations or the relevant authority, depending on risk.
8.5.4
Prevention of septicity
Septicity caused by the prolonged retention of wastewater under anaerobic conditions is undesirable and
should be avoided by limiting the time of retention in rising mains, sewers/detention tanks and siphons and by
the provision of self-cleansing conditions in sewers to achieve aerobic conditions within the liquid. Where this
is not possible or effective, intervention can be necessary by using, for example, chemical oxidation and/or
precipitation. The choice of chemicals shall take account of their potential environmental impact.
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Septic wastewater can produce lethal or explosive gases, particularly hydrogen sulfide (H2S) and methane
(CH4) and lead to offensive odours, chemical attack, difficulties in wastewater treatment processes, safety
hazards and danger to life.
8.5.5
Combined sewer overflows and surface water treatment
Combined sewer overflow and outfall structures shall be designed to minimise the impact of any discharges
on the environment.
Overflows are normally necessary on combined sewer systems. Close to the entrance of the wastewater
treatment plant overflows are installed on separate sewer systems for use under exceptional circumstances.
The site and discharges, from these and other outfalls, to receiving waters shall be controlled to limit pollution.
Various methods such as flow detention and sedimentation can be used to assist in limiting pollution inputs to
receiving waters. Factors to be considered include:

flow rates;

volume, duration and frequency of discharges;

pollution concentrations and loads;

hydro-biological stress;

aesthetic impacts.
The pollution discharges to receiving waters from overflows and treatment works shall be considered together.
Detailed consideration of the environmental impact of combined sewer overflows and surface water treatment
is described in 9.4.7.
8.5.6
Emergency overflows
Emergency overflows can be installed immediately upstream of wastewater treatment plants, at pumping
stations and at other critical parts of the system.
The environmental impact of such overflows shall be considered.
8.6 Structural Design
8.6.1
Introduction
The structural design of the system shall ensure that the design meets all relevant functional requirements
including:

Prevention of noise and vibration (see 5.1.7);

Sustainable use of products and materials (see 5.1.8);

Structural integrity and design life (see 5.1.10);

Not endangering adjacent structures and utility services (see 5.1.13).
The structural design of drain and sewer systems shall take account of:

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
watertightness of the drain and sewer system (see EN 1610);

prevention of floatation;

bearing capacity of the soil;

chemical nature of the soil will have an effect on the materials used;

effect of aggressive, corrosive and/or erosive wastewater on the materials used;

possible differential settlement between structures and all drains and sewers and outgoing rising mains
and other services;

any requirements of national or local regulations or the relevant authority.
Where buildings are near to drains or sewers or where a building is proposed near a drain or sewer the design
should consider:

effect on the sewer of the building; and,

effect of failure of the sewer on the building.
8.6.2
Structural design of pipelines
The structural design of buried pipelines shall be carried out in accordance with one of the methods described
in EN 1295-1 or otherwise designed in accordance with EN 1990 to EN 1999 if applicable.
In the case of renovation, a partial structural contribution of the existing pipe may be taken into account only if
the soil and pipe fabric is stable and when this contribution can be quantified.
Where common trenches for drains or sewers and other utility services are used care shall be taken to ensure
the stability of the pipes.
Where a pipeline is to be laid close to foundations of a structure, the potential effects of the structure on a
pipeline shall be considered. Care shall be taken to ensure that the foundations are not undermined or
damaged.
8.6.3
Structural design of other components
The structural design of other components of drain and sewers systems shall be designed in accordance with
EN 1990 to EN 1999 if applicable, or otherwise in accordance with relevant product standards.
8.6.4
Materials selection
The selection of an appropriate material is an important part of the design of the structure. The durability of
materials used in the construction of components of drain and sewer systems can be affected by the chemical
action of groundwater and the wastewater. In some conditions the material can also be affected by the
physical and chemical action of sediments contained in the wastewater.
In selecting materials designers shall consider:

chemical content of the wastewater,

possible presence of hydrogen sulfide (see 9.5.3),

abrasive nature of any sediments carried in the wastewater,
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
corrosive properties of any sediments and the effect of chemicals they could generate,

chemical content of the ground and groundwater,

physical properties of the soil,

environmental impact of chemicals released during installation.
8.7 Operational Considerations
8.7.1
General
The operational considerations of the design shall ensure that the design meets all relevant functional
requirements including:

Protection from flooding (see 5.1.2);

Maintainability (see 5.1.3);

Prevention of odours, toxic, explosive and corrosive gases (see 5.1.6);

Prevention of noise and vibration (see 5.1.7).
Planning, design, construction and rehabilitation shall take into account the operation and maintenance
requirements.
The system shall be designed to minimise the risks to the health and safety of operator personnel.
The cost of maintenance of the system shall also be considered. When balancing the construction costs with
future maintenance costs, the whole life cost should be minimised.
8.7.2
Separators
Where appropriate, separators shall be provided on or near inlets to exclude or minimise the entry of solids or
other materials that could impair the operation of the drain or sewer system. These can include:

Grit separators to limit entry of sediments which could accumulate in the system restricting the flow;

Grease separators to limit the entry of fats and grease which could be deposited in the system restricting
the flow;

Light liquid separators to limit the entry of flammable liquids which could cause a hazard in the drain and
sewer system.
National or local regulations can require provision of separators.
Detailed design of separators is described in 9.6.2.
8.7.3
Self-cleansing conditions
Wastewater is likely to contain a variety of materials that could accumulate in drains and sewers or cause
blockage.
Drains and sewers shall be designed to minimise the risk of blockage from any material permitted in
wastewater.
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The build up of permanent deposits of solids in drains or sewers can significantly increase the risk of flooding
and pollution. Drains and sewers shall be designed to provide sufficient shear stress to limit the build up of
solids to levels which do not significantly increase this risk.
Special maintenance provisions can be required to ensure frequent sewer cleaning on sewers where it had
not been possible to provide self-cleansing conditions.
8.7.4
Access to drains and sewers
Safe access shall be provided at reasonable intervals to allow for inspection and maintenance. Manholes shall
be designed to facilitate safe entry and egress by operator personnel and to provide sufficient working space.
Wherever possible, provisions should be made for work to be carried out from surface level. National or local
regulations or the relevant authority can specify requirements for the access. Detailed design of the
operational considerations relating to access is described in 9.6.4.
9
Detailed Design
9.1 Introduction
Unless explicitly specified the requirements in this clause apply both for new construction and rehabilitation.
9.2 Layout and profile
9.2.1
Introduction
The principles for the physical design of drain and sewer systems are specified in 8.1.
9.2.2
Layout
The layout will be influenced by factors such as:
a) site conditions, environmental considerations, retained features and existing utility services;
b) protection of water abstraction areas;
c) availability of suitable sewers or outfalls;
d) layout of buildings, disposition of drainage systems inside buildings, appliances located on levels
necessitating direct connections to drains;
e) use of buildings served;
f)
planning and coordination of utility services;
g) social disruption during construction and its cost implications;
h) practical aspects of construction methods, working space, adequate protection and support;
i)
stability of building during and following construction of the drains and sewers;
j)
existing, planned and future development;
k) connections to or from existing drains and sewers which are to be retained;
l)
provision for phased construction and occupation;
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m) available gradients and depths of construction;
n) possibility of real-time control;
o) levels of receiving waters;
p) effects of tides, waves and currents;
q) groundwater levels;
r)
access for inspection and maintenance;
s) overland flood flow paths;
t)
obstacles from other infrastructure (e.g. utility services, railways, waterways, major roads);
u) land ownership;
v) proximity of trees and other vegetation.
The routing of drains and sewers to take into account such factors can have major consequences: e.g.
excessive depths or length, need of pumping or inverted siphons.
9.2.3
Accessibility
Manholes and inspection chambers should be in locations where they can be accessed by all those who could
have need to use them, having regard to the need for access in an emergency.
Where frequent access is required (e.g. pumping stations or CSOs with screens) or access by special plant
may be required (e.g. tanks, pumping stations or washout valve chambers) this should be taken into account
(see also 9.6.4).
Sewers serving more than one property should be at locations where the access for repair is possible.
9.2.4
Depth
The approximate depth is determined during the conceptual design and finalised during the detailed design.
Depth will have a significant effect on the cost of construction and maintenance. In deciding the method of
construction, the depth of drains and sewers shall be considered, in conjunction with other factors such as:

protection against flooding;

nature of the ground;

presence of groundwater;

proximity of foundations;

proximity of utility services;

proximity of trees or heavy root growth;

protection against frost;

minimum cover.
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9.2.5
Need for pumping
Circumstances which can make the pumping of wastewater either necessary or advisable include the
following:
a) avoidance of excessive depths of sewer;
b) drainage of low lying or other parts of the catchment area susceptible to flooding;
c) development of areas not capable of gravitational discharge to an adjoining drain or sewer system, a
wastewater treatment plant or an outfall;
d) overcoming an obstacle, e.g. a ridge, a watercourse, a railway or for avoiding the use of an inverted
siphon;
e) correction of difficulties in a drain or sewer system resulting from mining subsidence;
f)
provision of sufficient head for operation at a wastewater treatment plant;
g) centralisation of wastewater treatment;
h) raising wastewater to detention tanks.
Where part of a system cannot be effectively drained using a gravity system then consideration should be
given to the use of one or more pumping installations. The optimum number of installations shall first be
determined having regard to the whole life cost.
9.2.6
Pumping Installations
Where pumping installations are provided the design shall take into account:
a) whole life cost;
b)
energy usage;
c)
operations and maintenance requirements;
d)
risk and consequences of failure;
e)
health and safety of public and operating staff;
f)
environmental impact;
g)
nature of wastewater which can:

be aggressive, corrosive and/or erosive;

have a high solid content increasing the potential for blockage;

be toxic;

lead to potentially explosive conditions.
The design of the pumping station and the rising main shall take into account the interaction between them.
Where the wastewater is pumped consideration shall be given to the effects of the pump discharge rates on
the downstream parts of the system. Detailed design of pumping installations shall be designed in accordance
with Annex F.
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9.3 Preliminary Investigations
9.3.1
General
Attention needs to be paid to both the topographical features present in the localities concerned and to the
geological nature of the underlying strata.
9.3.2
Topography
Surface reconnaissance and examination of contour maps and aerial photographs will enable preliminary lines
for drains, sewers and rising mains to be established so that the general feasibility of the proposals can be
determined before detailed layouts and longitudinal sections are prepared. It is important to use any available
geological survey data in conjunction with contour maps when deep open-cut and trench-less options have to
be considered.
9.3.3
Geotechnical Survey
At the conception stage of the design an understanding of the ground conditions to be encountered during the
construction of the scheme is essential in order to be able to evaluate fully all the route and construction
options.
The aim in this initial geotechnical survey will be to gain broad information in the most cost effective manner.
As the project develops, more intensive investigations will be necessary.
Geological maps are, even with their limitations, a source of general information. Where these are inadequate,
a preliminary ground investigation should be undertaken.
The data gathered in a geotechnical survey should, as appropriate, be sufficient to be able to assess:
a) ground loadings on the pipes/structures;
b) landslide conditions;
c) subsidence conditions;
d) fine particle movement;
e) any likely swelling of clay strata;
f)
groundwater levels and movement;
g) aquifer recharge potential;
h) loadings from adjacent structures and highways;
i)
previous land use (including mining);
j)
alternative construction methods;
k) options in pipe type choice;
l)
pipe bedding options;
m) aggressive soil or groundwater conditions.
Soil and rock samples should be retained especially where tunnelling or other trench-less methods are
contemplated.
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9.3.4
Groundwater
Where appropriate, groundwater levels including seasonal variations shall be determined during
representative periods of time. Investigations shall be carried out to identify conditions which can be
detrimental to the integrity of the pipeline.
9.3.5
Existing drainage services
The lines, levels, hydraulic adequacy and structural condition of all relevant existing features (e.g. drains,
sewers, ditches, land drains and watercourses) shall be ascertained. When designing a rehabilitation project
the existing pipe shall be assessed in accordance with 6.4.
9.3.6
Other existing utility services
The positions of other existing relevant utility services shall be ascertained as accurately as possible.
9.3.7
Extraneous water
If the risk of extraneous water (e.g. infiltration) entering drains and sewers, is considered to be unacceptable,
investigations shall be carried out to determine the extent of this risk.
9.4 Hydraulic Design
9.4.1
Introduction
The principles for the hydraulic design of drain and sewer systems are specified in 8.4.
Drains and sewers shall be designed to provide sufficient capacity for the design flows. In selecting the
diameter and/or gradient of the pipe consideration shall also be taken of the need to minimise build up of
sediments and to minimise the risk of blockages (see 9.6.3)
9.4.2
Foul drains and sewers
Drain and sewer systems shall be designed to collect and transport wastewater influents from domestic, trade
premises to the point of treatment without prejudice to health and safety. Such design should also include
allowances for future growth and for extraneous discharges up to such flow that will justify rehabilitation.
a) Drain systems
The design of drains (and sewers) to serve individual or small groups of buildings where discharges from
individual appliances will give relatively high flows of an intermittent and irregular nature shall use a peak rate
of flow derived from the number and type of appliances connected.
The rates of flow in the drains from the buildings or premises, calculated using EN 12056-2, should be used in
the design of downstream drain systems.
Flow rates for individual appliances and factors to be applied can be specified by national or local regulations
or the relevant authority. Trade effluent flows shall be calculated separately.
Having completed the design of the drain system, the interaction between the drain and the sewer system
shall be checked.
b)
Sewer systems
For domestic wastewater sewers, flow rates are usually based on either by population and a rate of flow per
head or, for new developments where such data is not available, on the planning criteria for the population or
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the type and number of dwellings. For a new development and for an upgrading scheme on an existing
development, the estimates used shall be appropriate for the specified planning horizon.
Existing water supply statistics may be helpful to derive future water supply consumption and hence domestic
wastewater flows. Flow patterns for daily consumption and anticipated variations between different types of
development can also be established. Consumer water usage that does not enter the drain and sewer system
and distribution leakage are of particular importance in assessing domestic wastewater flows.
The rate of flow per head may be based on local water supply statistics allowing for consumption that does not
result in discharge to the sewers and, where appropriate meters are not available, distribution losses. Typical
discharge figures for developments similar to those under consideration may also be used. The flow per head,
in the range from 120 l/day to 400 l/day, commonly used in various countries is shown in Annex E, Table E.4.
The peak design flow takes account of the diurnal variation in domestic wastewater flow. The domestic peak
design flow rates commonly used in various countries are shown in Annex E, Table E.5. To these peak design
flows shall be added trade peak flows and, where unavoidable, extraneous flows.
Where a scheme is to be developed in phases, consideration should be given to the likely flows following the
initial stages of construction so that either self-cleansing conditions are attained at least at times of daily peak
flow or other cleansing arrangements are made.
9.4.3
Surface water drains and sewers
The hydraulic design of drains and sewers serving impermeable surfaces, such as roads and car parks, is
dependent on the hydraulic performance of the interface between the impermeable surface and the drain or
sewer system. The flow at this interface shall be adequately considered in order to minimise the impact of
flooding.
The hydraulic capacity of the pipes shall be calculated in accordance with Annex E.
It can be necessary to provide a means of flow detention to intercept and hold back temporary peak storm
discharges in order to avoid flooding. The effects of flow balancing within the drain and sewer system on the
performance of the wastewater treatment plant shall be taken into consideration. Arrangements for
maintenance and safety of these structures will be required.
Runoff shall be calculated taking into account a number of factors including:

design rainfall;

area that could drain to the inlets connected to the system:

extent of impermeable area;

extent of permeable area;

likely losses of runoff due to infiltration of rainfall into the ground;

likely increases in connected area.
The possible impact of climate change should also be considered.
A simple method of calculating the runoff from small areas is included in Annex E.
9.4.4
Combined drains and sewers
For combined drains and sewers, the design flow rate is made up of runoff, which is by far the predominant
component, plus an allowance for foul wastewater flows. The runoff component should therefore be estimated
using the methods outlined in 9.4.3. The foul wastewater component is estimated as described in 9.4.2. As the
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foul wastewater flows are usually considerably lower than the design flow rates, particular consideration
should be given to self-cleansing velocities during dry weather conditions.
9.4.5
Capacity of pipelines
Pipes shall be selected to:

transport the required design flows;

limit sediment build up (see 9.6.3);

ensure that the risk of blockage is reduced (see 9.6.3); and,

ensure that effective maintenance can be reasonably achieved (see 9.6.4).
Two equations are recommended for use in calculating turbulent flows in drains and sewers: Colebrook( )
( )
White 1 and Manning 2 , taking into account headlosses of the pipeline (see Annex E, E.2).
Two methods of calculating total headlosses are:

adding local headlosses (see Annex E, E.2.1.4.2) to the pipeline headlosses (see Annex E, E.2.1.4.1);

accounting for local headlosses by assuming a higher value of hydraulic pipeline roughness in the
calculation of pipeline headloss.
When using recommended hydraulic pipeline roughness values it is necessary to establish whether allowance
has been included for local headlosses. Values currently in use range from 0,03 mm to 3,0 mm for k
(Colebrook-White formula) and 70 m1/3s-1 to 90 m1/3s-1 for K (Manning formula).
In cases where deposits in the invert cannot be avoided, the reduced cross-section of the pipe shall be taken
into account when calculating headlosses.
9.4.6
Sewers with steep gradients
Where sewers with steep gradients are required, consideration shall be given to consequences of high
velocities such as:

air entrainment and its effects;

release of hydrogen sulfide;

erosion;

need for energy conservation measures on changes from super-critical flow to sub-critical flow;

special safety measures for operatives.
Backdrop manholes, ramp manholes or vortex manholes may be installed in a sewer system to dissipate
excessive static head in a controlled manner, thereby avoiding the installation of sewers with steep gradients
and meeting any imposed velocity limitation.
1 This equation is named Colebrook in the French version and Prandtl-Colebrook in the German version.
2 This equation is named Manning-Strickler in the French and German versions.
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9.4.7
Outfall Design Requirements
Where surface water is to be discharged to a surface receiving water, the invert level of the outfall should be
above the peak design water level of the surface receiving water so as to provide free discharge conditions.
Where periodic backflooding cannot be avoided, a non-return valve should be considered.
9.5 Environmental Considerations
9.5.1
Introduction
The principles of the environmental considerations for drain and sewer systems are specified in 8.5.
9.5.2
Outfall Design Requirements
Outfalls shall be so formed as to avoid, or provide protection against, local erosion. It can be necessary to
provide additional protection to the outfall opening to prevent damage, interference or entry. The visual impact
of the outfall shall also be taken into account.
9.5.3
Prevention of septicity
Septicity within a drain or sewer system is undesirable and therefore shall be minimised. It will affect the
wastewater treatment process and can lead to the production of hydrogen sulfide (H2S) and mercaptans.
Hydrogen sulfide is malodorous, toxic and potentially lethal even in small concentrations. Depending on its
concentration and local conditions it can be oxidized to sulfuric acid, it will tend to attack some materials in
pipelines, treatment works and pumping installations. Parameters on which the concentration of hydrogen
sulfide depend, and which shall be taken into account include: wastewater temperature, biochemical oxygen
demand (BOD), sulfate availability, retention time, flow velocity, turbulence, pH, ventilation, existence of rising
mains or particular trade effluent discharges upstream of the gravity sewer.
Predictive equations can be applied in order to quantify sulfide formation both in pressure and gravity sewers.
Other gases can also be produced from normal wastewater in anaerobic conditions as follows:
a) Methane has little odour and whilst it is a simple asphixiant by displacing oxygen, its main property is that
it produces an explosive mixture with air over a wide range of concentrations. A particular vehicle for
methane production is leachate from landfill sites which has been allowed to enter the drain or sewer
system. Such leachates could need to be treated at source.
b) Ammonia has a distinct and strong odour which gives good warning characteristics before reaching toxic
levels, which are themselves unlikely to be generated from normal wastewater.
c) Carbon dioxide has no odour and will act as an asphixiant by displacing oxygen.
d) Carbon monoxide is also odourless and is highly toxic and lethal after only limited exposure.
Production of all these gases can be limited by the application of strategies to reduce septicity.
Other gases can be produced under anaerobic conditions where particular trade effluents have been allowed
to enter the drain or sewer system.
Methods to control the effects of anaerobic conditions can be used, considering the potential distribution of
gases and their odours, including:

Natural or forced ventilation;

Natural or forced entrainment of air in the flow;
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
Addition of reagents to the flow.
9.5.4
Drains and sewers near water abstraction areas
Installation of drains and sewers can be restricted in areas where water is to be abstracted for human
consumption. If in such areas drain and sewer systems are unavoidable, the designer shall take measures to
ensure permanent control and to prevent pollution of the ground and/or groundwater. Such measures can
include:

installation of an additional equally watertight surrounding pipe;

installation of alarm systems for leakage and breakage;

installation of house connections directly to manholes and not to the sewer;

special requirements for system components and method of construction.
9.6 Operational Considerations
9.6.1
Introduction
The principles of the operational considerations for drain and sewer systems are specified in 8.7.
9.6.2
Separators
Separators shall be used where appropriate for example to minimise the entry of materials that can
accumulate in drains and sewers or otherwise cause a blockage.
a) Grit separators shall be provided on or near inlets where the wastewater is likely to contain significant
sources of grits or other sediments that could accumulate in drains or sewers.
b) Grease separators shall be provided where the wastewater is likely to contain significant volumes of
grease or fats. Grease separators shall comply with the requirements of EN 1825-1. The nominal size of
grease separators shall be selected in accordance with EN 1825-2.
c) Where wastewater is likely to contain significant volumes of light liquids (e.g. oil or petrol) separator
systems for light liquids shall be provided on or near inlets. In considering whether to provide a separator
system for light liquids, account shall also be taken of the likely environmental impact of oils that could be
discharged into surface receiving waters or groundwaters. Separators systems for light liquids shall
comply with the requirements of EN 858-1. The nominal size of separator systems for light liquids shall be
selected in accordance with EN 858-2.
9.6.3
Design for self-cleansing
9.6.3.1
Sediment transport
For small diameter drains and sewers (less than DN 300) self-cleansing can generally be achieved by
ensuring either that a velocity of at least 0,7 m/s occurs daily, or that a gradient of at least 1:DN is specified.
Steeper gradients or higher velocities can be required by national or local regulations or the relevant authority.
To achieve self-cleansing conditions in sewers with low gradients there should be strict CH27 requirements for
the bedding and accurate laying of the pipes.
For larger diameter drains and sewers, higher velocities can be necessary particularly if relatively coarse
sediment is expected to be present.
Local guidance, in the form of tables or equations can be available in national reference documents and may
be used.
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Where self-cleansing conditions cannot be achieved provision should be made for adequate maintenance
activities.
9.6.3.2
Minimisation of blockages
To minimise the risk of blockage, drains and sewers should be smooth and laid to self-cleansing conditions.
However where the flows in the drain or sewer are low, steeper gradients (up to 1:DN/2,5) can be required.
9.6.4
Access to drains and sewers
The principles for provision of access are described in paragraph 8.7.4.
The maximum spacing between access points should take account of the maintenance equipment and
practices likely to be used.
In the case of drains, access shall be provided where practicable, at every change of alignment or gradient by
means of manholes, inspection chambers and rodding points. Where this is not practicable, provision for
access shall ensure that changes of alignment or gradient can be reached.
In the case of non man-entry sewers, access shall be provided, where practicable, at every change of
alignment or gradient, at the head of all sewers, at every junction of two or more sewers, wherever there is a
change in the size of a sewer and in addition at reasonable intervals for inspection and maintenance. In
general, access should be provided through manholes. Inspection chambers may be used within the system.
In the case of man-entry sewers, access shall be provided at reasonable intervals to allow for inspection and
maintenance, having regard to the nature of the work to be undertaken and the proposed safe systems of
working.
Manholes and inspection chambers should be designed and installed so as to avoid any acute changes in
direction of flow from branch drains.
National or local regulations can specify requirements for the:
a) location and spacing of access points on drains and sewers;
b) positioning or the maximum spacing of manholes or inspections chambers;
c) dimensions of manholes or inspection chambers.
The dimensions for manholes and inspection chambers shall not be less than the minimum dimensions given
in EN 476.
EN 476 contains requirements for three types of chamber as follows:
d)
Manhole with access for cleaning and inspection by personnel – EN 476:1997, 6.1.1 requires that
manholes for all maintenance works with access for personnel have a DN/ID 1 000 mm or greater, or a
nominal size for rectangular sections of 750 mm x 1 200 mm, or greater, or a nominal size for elliptical
sections of 900 mm x 1 100 mm, or greater.
e)
Manhole with access for cleaning and inspection – EN 476:1997, 6.1.2 requires that manholes for the
introduction of cleaning equipment, inspection, and test equipment, with occasional possibility of access
for a man equipped with a harness, have a DN/ID of 800 mm or greater but less than 1 000 mm.
f)
Inspection or connection chamber – EN 476:1997, 6.1.3 states that inspection chambers having DN/ID’s
less than 800 mm permit the introduction of cleaning, inspection, and test equipment, but do not provide
access for personnel.
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National or local regulations or the relevant authority can prohibit entry of personnel into chambers below a
certain size.
10 Construction Principles
10.1 General
Drain and sewer systems shall be constructed in accordance with the design. Unless explicitly specified the
requirements in this clause apply both for new construction and rehabilitation. During construction the
following issues should be taken into account:
a) Health, safety and welfare of construction personnel and other people;
b) Optimum sequence of construction particularly with regard to maintaining the operation of existing drain
and sewer systems which could be affected by the work;
c) Methods of dealing with existing flows in part completed systems or when carrying out rehabilitation of
existing flows;
d) Protection of the environment.
10.2 Pipelines
In the case of new construction, pipelines shall be constructed in accordance with EN 1610 or EN 12889 as
appropriate.
In case of rehabilitation, pipelines shall be constructed according to the relevant installation manual (referring
to the corresponding system standards when existing).
In any case the following points should notably be accounted for:

pipelines geometry;

flow performance;

watertightness;

proper load transfer from soil to pipeline through embedment;

proper structural embedment.
Where common trenches for sewers or drains and other utility services are used, care shall be taken to
ensure the stability of the pipes.
Testing shall be carried out to verify that the work has been constructed in accordance with the design.
10.3 Ancillaries
Ancillaries, such as inspection chambers and manholes, should be constructed in order to ensure correct
junctions with the pipes (pipelines).
NOTE
Special care should be granted to differential displacements.
In any case the following points should notably be accounted for:

geometry;
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
flow performance;

water tightness;

proper structural embedment.
For ancillaries the performance requirements specified in relevant European product standards should be
taken into account. Grease separators shall be installed in accordance with EN 1825-2. Separator systems for
light liquids shall be installed in accordance with EN 858-2.
11 Operations and Maintenance
11.1 Introduction
The purpose of operations and maintenance is to ensure that the drain and sewer system perform in
accordance with the functional requirements defined in clause 5 and in accordance with any operations and
maintenance plan (see 6.4).
Operations include:

starting or stopping pumps;

inserting dam boards;

regulating valves and weirs;

using detention tanks;

acting in accordance with contingency and emergency plans;

measuring wastewater quality;

inspecting periodically;

pest control (see C.10);

making connections to existing drains and sewers (see C.11);

control of disused drains and sewers (see C.12);

control of building activities over or adjacent to sewers (see C.13).
Urgent interventions that are generally intended to be temporary are included in operations.
Maintenance includes:

local repair or local replacement of damaged pipes or other structures in order to maintain the functioning;

cleaning and removal of sediments, obstructions etc. to restore hydraulic capacity;

maintenance of mechanical plant (e.g. pumps).
Effective operation and maintenance of the drain and sewer system will depend on, for example:

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
rights of access;

sufficient number of competent personnel;

clear assignment of responsibilities;

suitable equipment;

knowledge of the system, its operational components and the users connected;

adequate records and analysis.
There can also be requirements relating to the resolution of performance deficiencies, for example to remedy
failures and problems within acceptable timescales.
11.2 Objectives
Operations and maintenance has the following objectives to:

ensure that the entire system is operationally ready at all times and functions within the performance
requirements;

ensure that the operation of the system is safe, environmentally acceptable, and economically efficient;

ensure that as far as possible the failure of one section of a sewer system will not adversely affect the
performance of the other parts.
11.3 Data requirements
Data shall be collected:

for management purposes;

for regulatory reporting purposes (e.g. properties at risk of flooding);

meet statutory requirements (e.g. maintaining plans showing the location of the public sewers).
It is possible to store a wide range of data on drain and sewer systems. However, collection, validation,
storage and updating the data can be expensive. The amount of data collected depends on the reasons listed
above.
The information can include:

inventory of the system including records of drains, sewers, manholes, pumping installations, combined
sewer overflows, detention tanks etc.;

details of permits for influents into the system (trade effluents, hazardous materials etc.);

details of permits to discharge from the system into receiving waters (combined sewer overflows,
pumping installations etc.);

records of inspections of the system (e.g. closed circuit television (CCTV) survey reports);

records of incidents such as blockages, collapses, pumping station failures, rising main failures and
flooding incidents;

information on rainfall;
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
records of planned maintenance work carried out;

actual response times for dealing with emergencies;

information on the cost of incidents and maintenance activities to allow budgetary control and
performance review;

information about the hydraulic capacity; and

records of system performance (see 6.2.3).
Computer based geographical information systems (GIS) are a powerful tool for storage retrieval and analysis
of information on sewer systems.
11.4 Investigation and analysis of operational problems
To deal with operational problems in the most cost effective way, it is necessary to investigate and understand
their causes and effects. Investigations can be required to determine:

route of a pipeline;

cause and location of the sediment, blockage or collapse;

cause and location of a surface depression;

location, source, quality of making of a connection;

quality of a repair;

condition of a pipe;

extent of scale or grease build up;

effectiveness of sewer cleaning work;

origin, quality and composition of influent;

quantity and composition of the wastewater;

presence of hazardous gasses;

watertightness.
Operational investigation techniques available include:

dye tracing;

electronic location (using radio transmitters and a directional receiver);

closed circuit television (CCTV);

walking through sewers;

mirrors;

flow measurement;
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
sampling and analysis;

insitu measurement of the composition of influent;

watertightness tests (see EN 1610).
Operational problems concern the various components of the drain and sewer system. The techniques
available to resolve them are described in Annex C.
12 Performance testing
It is necessary to test and assess the performance of the drain and sewer systems during construction, at the
completion of the construction stage and also during the operational life of the system.
Examples of tests and assessments are:
a) watertightness test with water;
b) watertightness test with air;
c) infiltration test;
d) visual inspection;
e) dry weather flow assessment;
f)
monitoring of inputs to the system;
g) monitoring effluent quality, quantity and frequency at point of discharge to receiving water;
h) monitoring within the system for toxic and/or explosive gas mixtures;
i)
monitoring of discharge from system to treatment works.
The tests to be undertaken to determine the performance being achieved by the drain or sewer system will
depend on whether it is a new system, a rehabilitated system, or an existing system being tested.
The effectiveness of maintenance should be assessed by comparing the performance of the drain or sewer
system with the requirements (see 5.1). In addition, for reactive maintenance, target response times can be
used as an assessment.
13 Qualifications and Training
Personnel at all levels shall have appropriate training to allow them to carry out their work safely and
competently. This on-going training shall introduce and explain relevant legislation and techniques. Training
shall be repeated periodically when required and should cover safety, technical and legal topics where
appropriate.
The owners of construction works (procuring entity for public work or private agent for a private contract, or
their designer) shall request a proof that the enterprise carrying out the work is sufficiently qualified for the
specific work.
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14 Sources of Additional Information
Various national organisations provide supplementary detail and guidance on the planning, design,
construction and maintenance of drain and sewer systems outside buildings.
Examples of the sources of relevant information include:

Complementary National Standards;

European, national or local regulations;

Guidance issued by professional or trade associations;

Guidance documents issued by national or local government organisations;

Suppliers of technical software.
A list of organisations that produce relevant supplementary guidance is given in Annex B.
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Annex A
(informative)
Relevant EU Directives
A.1 Introduction
There are a number of EU Directives that relate to these key objectives. A number of these have a wider
application to the European Economic Area.
A.2 Relevant Directives
Relevant EU Directives include:
a) Water Framework Directive (2000/60/EC) together with its daughter directives and other relevant
environmental directives including:
1)
Bathing Waters Directive (76/160/EEC);
2)
Urban Wastewater Treatment Directive (91/271/EEC).
b) Safety and Health Framework Directive (89/391) together with its daughter directives and other relevant
safety and health directives including:
1)
Noise at Work Directive (86/188/EEC);
2)
Machinery Directive (89/392/EEC);
3)
Work Equipment Directive (89/655/EEC);
4)
Personal Protective Equipment Directive (89/656/EEC);
5)
Manual Handling Directive (90/269/EEC);
6)
Display Screens Directive (90/270/EEC);
7)
Asbestos at Work Directive (91/382/EEC);
8)
Temporary or Mobile Sites Directive (92/57/EEC);
9)
Working Time Directive (93/104/EEC);
10) Explosive Atmospheres (ATEX) Directives (94/9/EC and 99/92/EC);
11) Work at Height Directive (2001/45/EEC);
12) Physical Agents (Vibration) Directive (2002/44/EEC).
c) Construction Products Directive (89/106/EEC);
d) Public Procurement Directive 2004/18/EC.
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Annex B
(informative)
Sources of Additional Information
B.1 National Standards Bodies
Details of national standards bodies that are CEN members and affiliates can be obtained from CEN.
CEN Management Centre
www.cen.eu
36, rue de Stassart
B-1050
Brussels
B.2 Austria
B.2.1 Regulatory Bodies
Bundesministerium für Land- und Forstwirtschaft,
Umwelt, und Wasserwirtschaft. (Federal Ministry for
Agriculture, Forestry, Environment and Water
Management)
www.lebensministerium.at
Stubenring 1
A-1012
Wien, Österreich
B.2.2 Other organisations
ÖWAV - Österreichischer Wasser - und
Abfallwirtschafts Verband.
(Austrian Water and Waste Management
Association)
Marc-Aurel-Strasse 5
A-1010
Wien, Österreich
70
www.oewav.at
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B.3 Denmark
B.3.1 Regulatory Bodies
Miljøstyrelsen
(Danish Environmental Protection Agency)
www.miljoestyrelsen.dk
Strandgade 29
1401 København K
Erhvervs- og Byggestyrelsen
(National Agency for Enterprise and Construction)
www.ebst.dk
Dahlerups Pakhus,
Langelinie Allé 17
DK-2100 Copenhagen Ø
Arbejdstilsynet
(The Danish Working Environment Authority (WEA))
www.arbejdstilsynet.dk
Landskronagade 33
DK-2100 København Ø
Vejdirektoratet
(Danish Road Directorate)
www.vejdirektoratet.dk
Niels Juels Gade 13
Postbox 9018
1022 Copenhagen K
B.3.2 Other organisations
Dansk Vand. Og Spildevandsforening
(Danish Water and Wastewater Association (DWWA))
www.danva.dk
Vandhuset
Danmarksvej 26
8660 Skanderborg
Ingeniørforeningen i Danmark (IDA)
(The Water Pollution Committee of the Society Of
Danish Engineers)
www.ida.dk
Kalvebod Brygge 31-33
DK-1780 Copenhagen V
Denmark
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DHI Institut for vand and miljø
(Danish Hydraulic Institute)
www.dhigroup.com/dk
Agern Allé 5
DK-2970 Hørsholm
Denmark
Teknologisk Institut
(The Danish Technological Institute)
www.teknologisk.dk/
Gregersensvej 1
DK – 2630 Taastrup
B.4 France
B.4.1 Regulatory Bodies
Ministère de l’Ecologie et du Développement Durable
(Ministry for Ecology and Sustainable Development)
20, rue de Ségur
75302 PARIS 07 SP
www.environnement.gouv.fr
B.4.2 Other organisations
Centre d’études sur les réseaux, les transports,
l’urbanisme et les constructions publiques (CERTU)
(Centre for the Study of Urban Planning,
Transportation and Public Facilities)
9, rue Juliette Récamier
69456 LYON Cedex 06
www.certu.fr
Comité Français pour les travaux sans tranchée
(FSTT)
French Society for Trenchless Technology
4, rue des Beaumonts
94120 FONTENAY SOUS BOIS
www.fstt.org
B.5 Germany
B.5.1 Regulatory Bodies
Bundesministerium für Umwelt, Naturschutz und
Reaktorsicherheit (BMU)
Federal Ministry for the Environment, Nature
Conservation and Nuclear Safety
Bonn Office:
Robert-Schuman-Platz 3
D - 53175 Bonn
72
www.bmu.de
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Berlin Office:
Alexanderstraße 3
D - 10178 Berlin
The Ministries of the relevant states.
B.5.2 Other organisations
Deutsche Vereinigung für Wasserwirtschaft,
Abwasser und Abfall (DWA)
(German Association for Water, Wastewater and
Waste)
www.dwa.de
Theodor-Heuss-Allee 17
D-53773 Hennef
Germany
B.6 Ireland
Regulatory Bodies
Department of the Environment, Heritage and Local
Government
http://www.environ.ie/
Custom House,
Dublin 1
Ireland
B.7 Italy
B.7.1 Regulatory Bodies
Ente Nazionale Italiano Di Unificazione - Uni
www.uni.com
Via Sannio, 2
20137 MILANO
B.7.2 Other organisations
ASPI – Associazione nazionale manutenzione e
spurgo di reti fognarie e idriche
www.associazioneaspi.it
Via S. Caboto, 2
33170 PORDENONE
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B.8 The Netherlands
B.8.1 Regulatory Bodies
Ministerie van Volkshuisvesting Ruimtelijke Ordening
en Milieubeheer
(Ministry of Housing, Spatial Planning and the
Environment
http://www.vrom.nl
PO Box 20951
2500 EZ DEN HAAG
Ministerie van Verkeer en Waterstaat
(Ministry of Transport, Public Works and Water
Management)
http://www.verkeerenwaterstaat.nl/
PO Box 20901
2500 EX Den Haag
B.8.2 Other organisations
Stichting RIONED Foundation
http://www.stichtingrioned.nl
PO Box 133
6710 BC Ede
NVA
Nederlandse Vereniging voor Waterbeheer
(Netherlands Association for Water Management)
http://www.nva.net
PO Box 70
2280 AB Rijswijk
Unie van Waterschappen UvW
(Association of Water Bodies)
www.uvw.nl
PO Box 93218
2509 AE The Hague
VNG
Vereniging van Nederlandse Gemeenten Association
of Netherlands Municipalities
De Willemshof
Nassaulaan 12
2514 JS Den Haag
74
www.vng.nl
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B.9 Norway
B.9.1 Regulatory Bodies
National Office of Building Technology and
Administration
http://www.be.no/
PO Box 8742 Youngstorget
NO 0028 Oslo
Norway
The Norwegian Pollution Control Authority (SFT)
http://www.sft.no/
PO Box 8100 Dep
NO 0032 Oslo
Norway
B.9.2 Other organisations
Norwegian Water and Wastewater BA
http://www.norvar.no/
Vangsvegen 143
NO 2317 HAMAR
Norway
B.10 Portugal
B.10.1 Regulatory Bodies
Ministério das Obras Públicas e Transportes, Lisbon,
Imprensa Nacional – Casa da Moeda
www.moptc.pt
Rua de São Mamede (ao Caldas), nº21
1149-050 Lisboa
Ministério do Ambiente, do Ordenamento do
Território e do Desenvolvimento Regional (MAOTDR)
www.maotdr.gov.pt/MAOTDR
Rua de «O Século», 51
1200-433 Lisboa
Instituto Regulador de Águas e Resíduos (IRAR)
Centro Empresarial Torres de Lisboa
Rua Tomás da Fonseca, Torre G - 8º
1600-209 LISBOA
www.irar.pt
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B.10.2 Other organisations
Laboratório Nacional de Engenharia Civil (LNEC)
www.lnec.pt
Av. do Brasil, 101,
1700-066 Lisboa
B.11 Sweden
B.11.1 Regulatory Bodies
The Swedish National Board of Housing, Building and
Planning, (Boverket)
www.boverket.se
Swedish Environmental Protection Agency
(Naturvårdsverket)
www.internat.naturvardsverket.se
The Swedish Work Environment Authority,
(Arbetsmiljöverket)
www.av.se
B.11.2 Other organisations
Svenskt Vatten
(Swedish Water and Wastewater Association)
Box 47607
SE-117 94 STOCKHOLM
Sweden
www.svensktvatten.se
B.12 Switzerland
B.12.1 Regulatory Bodies
D: Bundesamt für Umwelt (BAFU)
http://www.bafu.ch
F: Office fédéral de l'environnement (OFEV)
http://www.ofev.ch
Postfach, 3003 Bern
Gewässerschutz-Fachstellen der einzelnen Kanton
(Fachstellen von 26 Kantonen)
Die Post- und Internet-Adressen
www.kvu.ch erfragt werden.
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B.12.2 Other organisations
D: VSA, Verband Schweizer Abwasser- und
Gewässerschutzfachleute
F: VSA, Association suisse des
professionnels de la protection des eaux
www.vsa.ch
E: VSA, Swiss Water Pollution Control Association
Strassburgstrasse 10,
Postfach
CH-8026 Zürich
B.13 United Kingdom
B.13.1 Regulatory Bodies
B.13.1.1 General
Health and Safety Executive
www.hse.gov.uk
Rose Court
2 Southwark Bridge
London
SE1 9HS
B.13.1.2 England and Wales
The Department of Communities and Local
Government (Building Regulations)
www.communities.gov.uk
Eland House
Bressenden Place
London
SW1E 5DU
Department of the Environment, Food and Rural
Affairs
www.defra.gov.uk
Nobel House
17 Smith Square
London
SW1P 3JR
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The Environment Agency
www.environment-agency.gov.uk
Rio House
Waterside Drive
Aztec West
Almondsbury
Bristol
BS32 4UD
B.13.1.3 Scotland
Scottish Building Standards Agency (SBSA)
www.sbsa.gov.uk
Denholm House
Almondvale Business Park
Livingston
EH54 6GA
Scottish Environmental Protection Agency (SEPA)
www.sepa.org.uk
SEPA Corporate Office
Erskine Court
Castle Business Park
STIRLING
FK9 4TR
B.13.1.4 Northern Ireland
Department of Finance and Personnel (Building
Regulations)
http://www.dfpni.gov.uk/
Building Regulations Unit
Office estates and Building standards Division
th
10 Floor
River House
48 High Street
Belfast,
BT1 2AW
The Environment and Heritage Service
Environmental Protection
Calvert House
23 Castle Place
Belfast
County Antrim
Northern Ireland
BT1 1FY
78
http://www.ehsni.gov.uk/
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EN 752:2008 (E)
B.13.2 Other organisations
Water UK
www.water.org.uk
1 Queen Anne’s Gate
London
SW1H 9BT
Water Research Centre (WRc)
www.wrcplc.co.uk
Frankland Road
Blagrove
Swindon
Wiltshire
SN5 8YF
UK
Foundation for Water Research (FWR)
www.fwr.org
Allen House
The Listons
Liston Road
Marlow
Bucks
SL7 1FD
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Annex C
(normative)
Operations and maintenance
C.1 Introduction
The purpose of operations and maintenance is to ensure that the drain and sewer system performs in
accordance with the functional requirements defined in clause 5.
C.2 Operations planning
C.2.1 Inspection routines
Inspection routines, including frequencies, shall be established for the system, taking into consideration the
requirements and importance of each component. Routines shall include the inspection of:

pipelines including inspection chambers, manholes and outfalls, taking into account the gradient and/or
velocity;

pumping installations, according to potential risk and type of equipment;

overflows and detention tanks, taking into account storm frequency;

inverted siphons, depending on risk of blockage and potential consequences;

separators, according to technical requirements;

grit chambers, gullies etc., taking into account storm frequency, capacity and land use.
C.2.2 Operations procedures
Procedures for the operation of the components of the system should include plans for:

operation of pumping stations;

operation of any special components (e.g. vacuum or pressure installations within the system);

setting dam boards, valves and weirs;

operation of detention tanks;

showing the assignment of responsibilities for carrying out procedures.
C.2.3 Contingency Planning
Contingency planning is the process of setting out procedures to be used in case of breakdown of a part of the
system. It should also include procedures for dealing with major failures and other emergencies. Procedures
could be required for a range of possible incidents including:
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
accidental spillages of toxic, noxious or explosive substances;

discharge of special substances used in fire fighting;

failure of pumping stations or pre-treatment facilities;

flooding due to an exceptional rainfall event;

major sewer collapse.
Contingency plans shall include:

details of emergency services;

estimated times for response (in general terms);

lists of those to be notified;

location of available resources;

procedures to be followed (including protection of receiving waters and wastewater treatment plant).
The resource requirements will need to be determined, including:

personnel;

vehicles;

equipment;

materials.
These resources will sometimes need to be available at short notice. This can influence resourcing decisions
for normal operations and maintenance work.
C.3 Pipelines
C.3.1 General
The common problems associated with drains and sewers (man entry and non man-entry) can be divided into
two types, functional problems and structural problems.
C.3.2 Functional problems
Functional problems can include:

blockage - this usually occurs when sediments/debris are deposited within the sewer system, forming
obstructions and a reduced pipe capacity;

sedimentation - this can also lead to blockages;

encrustation - build up of mineral deposits on the wall of the pipeline;

grease - deposited on the wall of the pipeline;

intrusion of tree roots;
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
infiltration or exfiltration caused by structural problems (see C.3.3);

failure of air valves and other protection systems (for rising mains).
Examples of available methods are:

jetting;

winching;

rodding;

cleaning balls;

remote controlled equipment;

flushing;

manual methods.
When carrying out cleaning activities consideration shall be given to the potential impact of the work on the
receiving wastewater treatment plant. Measures shall also be taken to avoid discharges of heavily polluted
matter to receiving waters through combined sewer overflows.
Residues from maintenance activities on drain and sewer systems shall be disposed of in accordance with the
requirements of national or local regulations or the relevant authority in such a way as not to cause pollution.
In severe cases, rehabilitation can be necessary.
Cleaning activities in drains and sewers shall be carried out in accordance with EN 14654-1.
C.3.3 Structural problems
Structural problems can include:

collapse;

cracking or fracturing of the pipe;

chemical attack or corrosion;

ground erosion outside the wall of the pipe - usually caused by infiltration of soil into the pipe;

defective connections;

pipe deformation;

open or displaced joints between pipes.
The following methods can be used to deal with the problems described above:

repair;

renovation;

replacement.
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Where problems are widespread or a significant length of sewer is involved a drainage area study (see clause
6) of the whole catchment area or part of it should be considered.
C.4 Manholes and Inspection Chambers
Manholes and inspection chamber are needed for access to sewers and drains for maintenance and
operations. The problems include:

defective covers - these include covers which are broken, cracked, ill-fitting or are not flush with the
ground level;

problems with access - e.g. inadequately sized access shaft, or defective steps or ladders;

structural problems with the fabric of the chamber including chemical attack and infiltration;

sediment in the invert;

odours or gas/oxygen deficiency.
These can be solved by works such as:

cleaning;

replacement and resetting of the covers;

repair, renovation or renewal of the fabric of the chamber;

reconstruction of access;

replacement of steps or ladders;

efficient ventilation.
C.5 Combined sewer overflows
The purpose of combined sewer overflows is to spill excess flows from a system to receiving water (see 8.5
and 9.4.7).
Problems associated with combined sewer overflows include:

blockages;

siltation of the chamber;

fouling of screens;

structural problems.
Blockages can be caused by:

restriction in size of the downstream sewer resulting in low flow velocity upstream leading to silting; and,

general build-up of silt/debris in the chamber.
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Siltation can be minimised by:

high pressure water jets to clean the chamber;

high volume suction units to remove debris;

flushing of the chamber.
Planned maintenance can be necessary in order to limit the environmental impact to satisfy the requirements
of national or local regulations or the relevant authority. The problem can be solved using planned
maintenance procedures, which includes inspection and reporting. From the report, work can be given a
priority and inspection frequencies determined.
Screens, where fitted, can require cleaning following heavy storms.
Structural problems arising may be dealt with in a similar fashion to structural problems in manholes.
C.6 Detention tanks
The role of the detention tank is to reduce peak flows by the temporary storage of wastewater within the
system. They are often used to reduce flooding and to reduce discharge and pollution load from combined
sewer overflows. The problems include:

blockage of flow control devices;

removal of sediment.
Methods of optimising the removal of sediments are:

modifications to the structure of the tank e.g. by use of low friction coatings (these shall not be used on
areas required for access as it can be a hazard to operatives);

modification of inlet design to increase scour;

modification to the benching or installation of dry weather flow channels;

use of mechanical plant in the tank to periodically remove sediments.
Where a blockage has occurred and wastewater has been detained for some time, clearing the blockage
suddenly can have an unacceptable impact on the wastewater treatment plant. Consideration shall be given to
the gradual emptying or removal of effluents from the tanks.
C.7 Separators, settling chambers and gullies
Separators are used to intercept light liquids e.g. oil, petrol, etc., grease or solids. Planned maintenance of
separators is required if they are to function efficiently.
Grit separators, settling chambers and gullies are often used to prevent sand and gravel from entering the
system.
Separators, settling chambers and gullies shall be emptied periodically to prevent blockage, especially after
spillages and, where appropriate, severe storms.
Separator systems for light liquids shall be operated and maintained in accordance with EN 858-2. Grease
separators shall be operated and maintained in accordance with EN 1825-2.
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C.8 Pumping installations
The main problems associated with pumping installations are as follows:

blockage of pumps, valves, screens etc. by debris;

power failure;

failure of rising main;

electrical or mechanical failure of a component of the pump, its control equipment, or telemetry unit;

crust formation inhibiting the operation of control devices;

noise and/or vibration;

odour complaints;

excessive power consumption;

vandalism.
To minimise maintenance and operations requirements and costs, careful attention needs to be given to the
design of the pumping station and its equipment. Where the composition or volume of flows have changed
substantially or where equipment is coming to the end of its life a reconsideration of the design is necessary
(see Annex F).
Solutions to some of these problems include the following:

repair or replace the pumping equipment;

reduce extraneous water;

installation of warning or telemetry systems;

installation of septicity prevention plant or ventilation of wet well;

review of the control system;

installation of standby power supplies.
In addition the installation of warning or telemetry systems can help reduce the impact of failure by allowing
early correction of actual or incipient failures.
C.9 Inverted siphons
The main problem associated with inverted siphons is sedimentation and blockage of the pipe. Planned
inspection and maintenance should be carried out to ensure that inverted siphons continue to operate
efficiently.
Inspection can include:

checking that washout valves and pumps can be operated;

checking for surcharging at the upstream end of each pipe, which can be a sign of partial blockage;

visual inspection of pipelines.
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Cleaning methods can include:

high pressure water jets;

high volume suction units to remove debris;

flushing of the inverted siphon;

use of cleaning balls.
C.10 Pest control
The principal pest problem in sewers is related to rats, though in some areas especially where there is
insufficient ventilation, or deposits of faecal sediments, insects such as cockroaches or mosquitoes can also
be a problem.
Since the sewer network can be a refuge for rats, control of rodents is needed to minimise health risks
(including Leptospirosis and Salmonella) and to prevent structural damage caused by burrowing.
Treatment programmes should be carried out in accordance with the requirements of national or local
regulations or the relevant authority, to control the infestation. To ensure maximum effectiveness treatment
programmes for sewers and drains should be carried out on a catchment wide basis and should be coordinated with the treatment of surface infestations.
Areas for treatment should be identified, in collaboration with national or local regulations or the relevant
authority and by reference to records of sightings of rodents. Areas may also be categorised according to the
risks to public health. The treatment programmes should be recorded and the effectiveness measured so that
records can be used to plan future programmes.
C.11 Making connections to existing drains and sewers
A large proportion of structural problems on drains and sewers are associated with poorly made lateral
connections. Problems are particularly common where manholes, inspection chambers or pre-formed
junctions are not used.
The control of new connections shall be undertaken to ensure that:

fabric of the drain or sewer is not weakened or damaged by the connection;

no operational problems are caused by the connection;

sewer is inspected at the point of connection before and after construction;

system is watertight at the point of connection;

connections are made to the correct sewer, where there are separate sewer systems.
Connections other than at manholes or inspection chambers should be made using pre-formed junctions.
New connections to brick sewers should be avoided, however if one is necessary, a thorough inspection of the
sewer shall be made beforehand.
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C.12 Control of disused drains and sewers
Disused drains and sewers shall be removed or, where this is impracticable, they shall be filled with suitable
material to prevent, for example, structural deterioration, unauthorised use, ingress of groundwater or
infestation by rodents.
C.13 Control of building over or adjacent to sewers
The construction of buildings in close proximity to drains and sewers should be controlled in order that the
operation and maintenance of the sewer system is not impaired by:

excessive loading leading to structural failure of part of the drain or sewer system;

prevention of access by maintenance personnel or equipment to manholes or inspection chambers,
wastewater pumping stations, or other ancillary structures;

prevention of access by maintenance personnel or equipment for excavation to a repair a defect on a
pipeline;

creating an undue risk of failure of the building in the event of a structural failure of the drain or sewer;

obstructing an overland flow path leading to an excessive risk of flooding in the building.
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Annex D
(normative)
Health and Safety
D.1 Safe systems of work
Employers shall, so far as is reasonably practical, provide and maintain systems of work that are safe and
without risks to health. The systems of work shall cover all aspects of the works including above-ground
operations (for example manhole location and traffic control), access to the sewer system and all operations in
the confined space of the sewer system. There shall be a written plan detailing systems of work for rescue
and emergency evacuation procedures. Employers shall also set out procedures for detection and prevention
of sudden inflows of toxic, flammable or potentially explosive substances, hot liquids or flood water discharged
into the sewer system. Special precautions shall be taken when entering inverted siphons.
The team size shall be sufficient to ensure that suitably trained personnel are:

on the surface to summon assistance and/or effect a rescue should it become necessary;

on the surface and in manholes to ensure that there is communication between personnel in the sewer
and both the entry and exit manholes.
D.2 Training and supervision
All personnel shall have appropriate training to enable them to carry out their work safely. In particular, all
personnel involved in sewer work shall have appropriate training in safety procedures for work in confined
spaces. Supervisors shall be competent in the management of work in the confined space of drains and
sewers.
D.3 Hazardous atmospheres
D.3.1 Oxygen deficient and toxic atmospheres
A range of oxygen deficient or toxic atmospheric conditions can occur in sewer systems. Appropriate
atmospheric monitoring equipment must be used continuously whilst any worker is in the system. Forced
ventilation should be used to maintain an atmosphere fit for respiration.
D.3.2 Potentially explosive atmospheres
The so-called “ATEX” Directives 94/9/EC and 99/92/EC apply to equipment and protective systems for use in
potentially explosive atmospheres and to work in potentially explosive atmospheres respectively. Directive
94/9/EC sets out requirements for the classification of equipment for use in a range of potentially explosive
atmospheres along with requirements for the protective systems to be applied to that equipment. Directive
99/92/EC sets out requirements for the classification of workplaces in which a potentially explosive
atmosphere can occur and for worker safety in such atmospheres.
A potentially explosive atmosphere can occur at any time during the operation of a sewer system, and this
should be addressed as part of the design of the system. Appropriately protected plant and equipment along
with their power and control systems should be specified and installed. The build up of potentially explosive
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atmospheric contaminants should be avoided by the use of forced ventilation coupled with adequate
atmospheric monitoring.
Whilst concentrations of potentially explosive atmospheric contaminants can build up when workers are
already in the sewer system, and evacuation should then take place in accordance with the nationally
recognized action limits, entry to the system should not take place when hazardous concentrations of
potentially explosive contaminants exceed 10 % of their lower explosive limits or the permissible national limits.
Additional national or local requirements can apply.
D.4 Traffic control
Measures shall be taken to warn and control traffic. These shall comply with the requirements of national or
local regulations or the relevant authority and can include the provision of warning road signs and flashing
beacons.
D.5 Protective equipment and welfare facilities
All necessary ventilation, lighting, communication and lifting equipment and, rescue equipment shall be
provided and shall be appropriate to the task undertaken. Personal protective equipment including appropriate
protective clothing and warning clothing shall be provided.
All persons employed in work which involves entry into manholes or sewers or contact with raw wastewater
shall have access to washing and showering facilities.
Self rescuers and first aid equipment shall also be provided.
D.6 Emergency procedures
Breathing apparatus shall be available on site and the team shall be sufficiently trained in its use to escape or
be able to affect rescue in the event of oxygen deficiency or operatives inhaling toxic or asphyxiating gases.
In the event of a collapse of a person in a confined space, no-one shall attempt to enter the confined space to
attempt a rescue without breathing apparatus.
When the working area could be flooded a warning and evacuation procedure shall be foreseen, and the
organization of the working area shall take into account these constraints.
D.7 Temporary works
Temporary works and arrangements for dealing with flow shall be designed with safety in mind. Care shall be
taken to ensure that exhaust fumes from pumps or other machinery are kept away from manholes and that
any dams or stoppers are sufficiently robust to withstand any hydraulic pressure likely to be applied while in
use.
D.8 Excavation work
When carrying out excavation work precautions shall be taken to avoid any danger to persons caused by
collapse of the sides of the excavation, and to avoid damage to other utility services in the proximity of the
excavations. Due regard shall also be taken to the need for safe operation of machinery and in particular the
need for adequate working space.
NOTE
EN 1610 provides guidance on trenching work.
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D.9 Hazardous materials
The use of materials and chemicals in sewer renovation work, which can be toxic, flammable, or irritate
human skin or internal organs, or are otherwise hazardous, should be minimised. When handling, storing, or
using hazardous materials, the system of work shall deal specifically with the precautions necessary, including
particular reference to their use in confined spaces. Processes can also generate dusts and fumes. Careful
checks shall be made on the levels of harmful atmospheric contaminants and appropriate remedial measures
taken where necessary.
D.10 Vaccinations
National or local regulations or the relevant authority can require vaccination (e.g. against polio, tetanus) for
personnel working in contact with foul wastewater.
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Annex E
(normative)
Hydraulic Design
E.1 General
E.1.1 Introduction
For smaller schemes a relatively simple, but safe, approach is recommended, though use of simulation
models is not excluded. Sewers are usually designed to run full, without surcharge, for relatively frequent
storms in the knowledge that this provides protection against flooding from much larger storms. For these
schemes the "design storm frequency" criteria in Table 2 should be used in the absence of any specified by
national or local regulations or the relevant authority. The designer shall use rainfall intensity and duration
figures applicable to that particular area.
For larger schemes and for smaller schemes to be designed using a simulation model and for larger schemes,
particularly where damage or public health risks are significant, it is recommended that the level of flooding
protection be directly assessed. The sewer system may be initially designed, as above, to give no surcharge
with an appropriate "design storm frequency". A sewer flow simulation model should then be used to check
the level of flood protection against the "design flooding frequency" and the design adjusted where the
required flooding protection is not achieved. There will be cases, however, where adjustments are appropriate
to avoid unnecessary over-design. Any requirements from national or local regulations or the relevant
authority shall be followed, but in their absence the design flooding frequency values given in Table 3 should
be used.
E.1.2 Selection of Flow Simulation Method
E.1.2.1
General
A variety of methods have been developed to assist in the design of drain and sewer systems. In all cases the
runoff process has been simplified to enable the design parameters to be estimated cost effectively. This
annex reviews the range of methods available and gives guidance where they should be used.
E.1.2.2
Flow simulation methods
Three levels of sophistication for the hydrodynamics of flow in pipes are recognised:

Simple/empirical methods
In these methods the flow is regarded as uniform and steady. The velocity at full flow conditions may be
used to compute a travel time (time of concentration). They are used primarily for design of small
development schemes (see E.3).

Kinematic wave methods
In these methods uniform unsteady flow can also be simulated. Lag time and in-pipe storage are taken
into account, but the methods cannot simulate unsteady flows. They are effective for the initial design of
large schemes, for the checking of existing systems, or for the simulation of network performance under
long series of storm rainfall.
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 Dynamic wave methods
In these methods non-uniform, unsteady flow can also be simulated even under conditions of surcharge
and backwater. They can be used to check the performance of systems under conditions of flooding.
For each level the aboveground hydrological processes can be treated in either a simple or detailed manner
(S or D in Table E.1 below).
Table E.1 gives guidance on the applicability of the methods. Methods may be combined for sub-catchments.
Table E.1 — Applicability of flow simulation methods
Application
Method
Simple
Empirical
Methods
Kinematic
Wave Methods
Dynamic Wave
Methods
Design of small development schemes
S
S
b
Design of large schemes
a
S
S or D
S
–
–
Checking performance against flooding
a
a
S or D
Checking existing systems
a
S or D
S or D
Planning of outfalls//overflows
a
S or D
S or D
Impact on receiving water quality
a
S
S or D
Impact on receiving water quantity
a
S
S or D
Real-time control of a system
a
S or D
S or D
Hydraulically
systems
NOTE
a
b
S
D
simple
road
drainage
Hydrological processes treated in simple manner.
Hydrological processes treated in detailed manner.
Not applicable.
Generally not recommended.
E.2 Hydraulic calculations
E.2.1 Velocity equations
E.2.1.1
General
The basis for design is that flows in drains and sewers are turbulent. Two equations are recommended for use
( )
( )
in calculating turbulent flows in drains and sewers: Colebrook-White 3 and Manning 4 .
3 This equation is named Colebrook in the French version and Prandtl-Colebrook in the German version.
4 This equation is named Manning-Strickler in the French and German versions.
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E.2.1.2
The Colebrook-White equation
For circular pipes flowing full, the velocity of flow is given by the equation:
 k

2,51ν

v = −2 (2 gDJ E ) log10 
+
 3,71 D D (2 gDJ ) 
E 

(E.1)
where
v
is the velocity averaged across the flow cross-section, expressed in metres per second (m/s);
g
is the gravitational constant, expressed in metres per second squared (m/s );
D
is the internal pipe diameter, expressed in metres (m);
JE
is the hydraulic gradient (energy loss per unit length), dimensionless;
k
is the hydraulic pipeline roughness, expressed in metres (m);
ν
is the kinematic viscosity of fluid, expressed in metres squared per second (m /s).
2
2
For partially full pipes or pipes with non-circular cross-sections the velocity of flow is given by equation (E.1)
by replacing D by 4Rh where Rh is the hydraulic radius (flow cross-sectional area divided by the wetted
perimeter).
E.2.1.3
The Manning equation
For both circular and non-circular cross-sections whether running full or partially full, the velocity of flow is
given by the equation:
v = KRh 2 / 3 J E 1/ 2
(E.2)
where
K
1/3
is the Manning coefficient, expressed in metres raised to the power one third per second (m /s) ;
Rh is the hydraulic radius, expressed in metres (m);
JE
is the hydraulic gradient (energy loss per unit length), dimensionless.
E.2.1.4
E.2.1.4.1
Headlosses
Pipeline headlosses
The hydraulic pipeline roughness (k) or the flow coefficient (K) allows for headlosses due to pipe material,
discontinuities at the joints and slime growth on the pipe surface below the water level.
E.2.1.4.2
Local headlosses
Headlosses, in addition to those mentioned in E.2.1.4.1, occur at junctions, changes of cross-section,
manholes, bends and other fittings. If direct calculations are to be made, the following equation shall be used:
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k v2
hL = L
2g
(E.3)
where
hL
is the local headloss, expressed in metres (m);
kL
is the headloss coefficient dimensionless;
v
is the velocity of the liquid, expressed in metres per second (m/s);
g
is the gravitational constant, expressed in metres per second squared (m/s).
E.2.1.4.3
Total headlosses
Two methods of calculating total headlosses are:

adding local headlosses (see E.2.1.4.2) to the pipeline headlosses (see E.2.1.4.1);

accounting for local headlosses by assuming a higher value of hydraulic pipeline roughness in the
calculation of pipeline headloss.
When using recommended hydraulic pipeline roughness values it is necessary to establish whether allowance
has been included for local headlosses. Values currently in use range from 0,03 mm to 3,0 mm for k and 70
1/3 -1
1/3 -1
m s to 90 m s for K.
Approximate comparisons of velocity estimates using equations (E.1) and (E.2) above may be made using the
following equation:
1
 32  6
 3,7 D 
K = 4 g   log10 

D
 
 k 
(E.4)
where
1/3
K
is the Manning coefficient, expressed in metres raised to the power of one third per second (m /s);
g
is the gravitational constant, expressed in metres per second squared (m/s );
D
is the internal pipe diameter, expressed in metres (m);
k
is the hydraulic pipeline roughness, expressed in metres (m).
2
E.2.2 The Saint Venant equations
The flow conditions may be calculated by application of the Saint Vennant equations. These partial differential
equations describe the gradually varied unsteady, non-uniform flow in open and closed channels. There are
two equations; the dynamic equation, and the continuity equation. Depending on the application and the flow
conditions different levels of simplification may be applied. These equations are shown in Table E.2 at various
levels of simplification.
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Table E.2 — The Saint Venant equations
Type of flow
Dynamic equation
gradually
varied
non-uniform
discontinuous
cvq
+
gA
Nr
Continuity
equation
Nr
1 δv
×
+
g δt
v δv
×
+
g δx
δh
=
δx
JS − JF
(E.5a)
δQ δA
+
=q
δx δt
(E.5a)
gradually
varied
non-uniform
1 δv
×
+
g δt
v δv
×
+
g δx
δh
=
δx
JS − JF
(E.5b)
δQ δA
+
=0
δx δt
(E.5b)
gradually
varied
simplified
non-uniform
1 δv
×
+
g δt
δh
=
δx
JS − JF
(E.5c)
δQ δA
+
=0
δx δt
(E.5b)
δh
=
δx
JS − JF
(E.5d)
δQ δA
+
=0
δx δt
(E.5b)
δh
=
δx
JS − JF
(E.5e)
δQ δA
+
=0
δx δt
(E.5b)
δh
=
δx
JS − JF
(E.5d)
δQ
=0
δx
(E.5c)
δh
=
δx
JS − JF
(E.5e)
δQ
=0
δx
(E.5c)
0= JS − JF
(E.5f)
δQ
=0
δx
(E.5c)
v δv
×
+
g δx
simplified
gradually
varied
non-uniform
simplified
gradually
varied
simplified
non-uniform
v δv
×
+
g δx
steady-state
non-uniform
steady-state
simplified
non-uniform
steady-state
uniform
(normal
discharge)
Term ref (see
below)
5
4
3
2
1
–
–
–
where
3
Q
is the flow, expressed in metres raised to the power of three per second (m /s);
q
is the lateral inflow per unit of length in the direction of the flow (assumed steady state), expressed in
3
metres cubed per second metre (m /(s.m));
A
is the flow cross-section perpendicular to the sole, expressed in metres squared (m );
JS
is the sole gradient (with open channel possibly not constant), dimensionless;
JF
is the friction gradient, dimensionless;
NOTE
2
For most practical purposes the friction gradient (JF) can be considered as equal to the hydraulic gradient (JE).
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x
is the path co-ordinate in direction of flow, expressed in metres (m);
t
is the time co-ordinate, expressed in seconds (s);
h
is filling height in profile or depth of water (perpendicular to sole) or the pressure head in completely
filled drains at the sole of the pipe or profile, expressed in metres (m);
v
is the mean velocity, expressed in metres per second (m/s), in a cross-section in the direction of flow;
g
is the acceleration due to gravity, expressed in metres per seconds squared (m/s );
c
is the factor with inclusion of additional losses, dimensionless.
2
The different terms in the dynamic equation can be described as follows:

Term 1 of the dynamic equation is the difference between the gradient of the invert of the pipe and the
friction gradient.

Term 2 of the dynamic equation is the kinematic wave term.

Term 3 of the dynamic equation is the diffusive wave term and takes into account backwater and wave
attenuation.

Term 4 of the dynamic equation is the local flow acceleration term.

Term 5 of the dynamic equation is the lateral flow inflow term.
E.3 Methods of calculating runoff from small development schemes
In the absence of a method specified by national or local regulations or the relevant authority, a simple
method of estimating the peak rate of discharge of surface water, applicable for areas of up to 200 ha or times
of concentration up to 15 min and assuming a uniform rate of rainfall intensity, may be used. The rainfall
intensity to be adopted will depend on factors such as time of concentration of the contributing area and the
analysis of local rainfall data. Peak flow rate is given by:
Q = C ⋅i ⋅ A
where
Q
is the peak flow rate, expressed in litres per second (l/s);
C
is the runoff coefficient (between 0,0 and 1,0), dimensionless;
i
is the rainfall intensity, expressed in litres per second hectare (l/s/ha);
A
is the area receiving rainfall (measured horizontally), expressed in hectares (ha).
Appropriate values for (C) are given in the Table E.3.
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Table E.3 — Runoff coefficients for calculating runoff from small development schemes
Runoff Coefficient C
Nature of connected area
Comments
Impermeable areas and steeply
sloping roofs a
0,9 to 1,0
Depending on depression
storage
Large flat roofs
0,5
Over 10 000 m
Small flat roofs
1,0
Less than 100 m
Permeable areas
0,0 to 0,3
Depending on ground slope
and cover
a
2
2
Impermeable areas may be increased by 30 % of large vertical surfaces.
E.4 Calculation of foul wastewater flows for drain systems
Wastewater flows for drain systems should be calculated in accordance with EN 12056-2.
E.5 Calculation of foul wastewater flows for sewer system
Table E.4 and Table E.5 give indicative values for average flow rate and peak design flow in common use for
the design of surface water and combined sewers.
Table E.4 — Domestic flow rate
Country
Flow rate Range
(l/head.day)
Comment
Czech Republic
100 to 150
Ordinary daily flow; does not contain
provision on infiltration.
Denmark
120 to 150
50 % to 100 % should be added to make
allowance for infiltration.
France
150 to 200
–
Germany
150 to 300
Depending on level and age of sanitary
system. No infiltration allowance included.
Netherlands
100 to 120
–
Portugal
120 to 350
–
Switzerland
170 to 200
–
United Kingdom
150 to 300
–
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Table E.5 — Domestic peak design flow
Country
Peak Design Flow
Comment
Denmark
4 l/s to 6 l/s per 1 000 inhabitants
Depending on the size of the catchment area,
excluding 50 % to 100 % infiltration allowance.
France
(1,5 to 4,0) x domestic flow rate
1,5 to 4,0 is the peak coefficient, it depends on
the location of the sewer, its gradient, its size
and the size of the town.
Germany
4 l/s per 1 000 inhabitants
For design of sewers.
Additional allowance made for infiltration, nondesigned flows.
4 l/s per 1 000 inhabitants or
200 l/inhabitant per day
For design of treatment
stormwater treatment.
works
and
for
Netherlands
–
10 % of daily flow.
Portugal
(2,0 to 5,0) x domestic flow rate
–
Switzerland
6 l/s to 7 l/s per 1 000 inhabitants
8 l/s to 10 l/s per 1 000 inhabitants often used to
include allowance for commercial flows.
United Kingdom
Up to 6 x domestic flow rate
Dependent on catchment area.
allowance made for infiltration.
Additional
E.6 Combined sewer overflows
The allowable discharges and impact of combined sewer overflows on receiving waters depend on local
conditions. Requirements are generally specified by national or local regulations or the relevant authority. The
location of combined sewer overflows, pollution loads, duration and frequency of discharges, pollution
concentrations and hydro-biological stress are factors to be considered. The impacts of combined sewer
overflows on receiving waters occur only for short time periods. However, they can be many times higher than
the impact and environmental loads from wastewater treatment plant. The main objective of combined sewer
overflow design, therefore, is to protect the receiving water without causing hydraulic overload of the sewer or
reduced treatment efficiency of downstream wastewater treatment plant.
Sewer flow simulation models (see 8.4) shall be needed to assess compliance with many of the specified
emission limits (see 8.5.2).
Two relatively simple approaches are available. A combined sewer overflow may be designed to begin
overflow discharge only after reaching a critical rainfall intensity, generally in a range of rates of 10 l/s ha
(impermeable area) to 30 l/s ha (impermeable area), depending on the degree of protection required.
Alternatively, when the self-purifying capacity is not at risk, a single criterion (commonly a dilution of 5 to 8
times dry weather flow before spill) may be used as an emission standard.
Associated storage in, for example, a detention tank, or length of tank sewer, can greatly reduce the
environmental impact of combined sewer overflows. Further reductions in environmental impact can be
achieved by partial treatment (e.g. settling).
If the retained flow in a combined system exceeds the capacity of the treatment works, it will be necessary to
incorporate storage or partial treatment of the retained flow. This may be sited at the treatment works or within
the sewer system.
In the design of a combined sewer overflow, steps shall be taken to keep the discharge of floating solids and
other unsightly material to acceptable levels. This can require the provision of baffles, screens or other means
of control.
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Annex F
(normative)
Pumping Installations
F.1 General
Pumping installations are occasionally required in gravity drain and sewer systems in order to avoid excessive
depths, or to drain low lying areas. They can also be necessary at combined sewer overflows or outfalls to
discharge flows into treatment works or receiving waters.
Pumping installations shall be designed in accordance with the principles described in clause 8.
NOTE
For layout, operation and maintenance requirements for lifting plants for wastewater within buildings and sites
requirements apply according to EN 12056-4.
Installations shall be planned and designed taking into account:
a) whole life cost;
b)
energy usage;
c)
operations and maintenance requirements;
d)
risk and consequences of failure;
e)
health and safety of public and operating staff;
f)
environmental impact;
g)
nature of wastewater which can:
 be aggressive, corrosive and/or erosive;
 have a high solid content increasing the potential for blockage;
 be toxic;
 lead to potentially explosive conditions.
F.3, F.4 and F.5 deal separately with the design of pumping stations, rising mains and components, however
these shall not be considered in isolation as there is interaction between them.
F.2 Planning of pumping installations
F.2.1 Preliminary Considerations
The preliminary considerations for each pumping installation shall include:

general location in relation to such features as flood plains, rivers, railways, major roads and overall
topography;
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
relation to existing sewer systems;

environmental considerations including the potential impact on any environmentally sensitive areas and
the siting of combined sewer overflows;

access requirements;

land ownership;

availability of power supply, water supply and telecommunications;

risk of explosion;

risk of flooding;

risk of floatation;

risk of saline infiltration;

suitability of geotechnical conditions.
Once these have been established consideration can be given to more detailed planning.
F.2.2 Planning
The requirements for the pumping installation shall be determined in accordance with the functional
requirements in clause 5, with particular reference to:

nature and quantity of flows including the range of flow rates (diurnal, dry/wet weather, etc.) and the
range of heads to be pumped;

effect of the flows on the downstream sewer system and treatment works;

measures to limit the impact of failure, which can include the use of standby pumps, generators, duplicate
rising mains, emergency overflows, screens, over-pumping arrangements, detention tanks, all including
the requirements of national or local regulations or the relevant authority;

requirements of national or local regulations or the relevant authority with regard to combined sewer
overflows and emergency overflows;

limiting noise and odour;

limiting retention time in order to avoid septicity and/or sedimentation;

provision of facilities and equipment for operation and maintenance;

requirements for future expansion;

consideration of special conditions (e.g. aquifer protection zones).
Once the requirements for the pumping installation have been determined, consideration can be given to the
requirements for the site and the location taking into account:

100
estimated size of the pumping station, relating to the number, size and type (e.g. centrifugal, screw or
ejector) of duty and stand-by pumps, whether there is to be a wet well/dry well, wet well only arrangement,
or duplicated wet wells;
BS EN 752:2008
EN 752:2008 (E)

space for detention tanks, screens or grit chambers if required;

space for future expansion of the pumping station;

access to the site in all weather conditions;

space for maintenance vehicles and ancillary equipment;

route and levels of the incoming and outgoing sewers;

environmental impact including odour, noise, visual impact, impact of discharge to receiving waters;

location of receiving waters for overflows if required;

risk of vandalism, site security and the need for fencing.
F.3 Design of pumping stations
F.3.1 Layout
Design requirements shall be determined for:

pumps;

drive units;

controls and electrical equipment;

instrumentation and telemetry;

alarms;

pipework and valves.
These shall take account of the basic requirements (see F.2). Consideration shall be given to:

maximum and minimum predicted flow rates to determine the duty points of the pumps and the size of
mechanical and electrical equipment;

type and number of pumps being used (At least two pumps should be installed to provide standby in the
event of failure of one pump);

fixed speed, multi-speed or variable speed drive units;

provision of screens, grit chambers or, where permitted, macerators at the inlet to minimise the risk of
clogging of, or damage to the pump impellers and downstream components;

removal of screenings and grit;

odour control;

physical size of the various items of plant such as pumps;

provision of access to, and sufficient working space around, all components which could require
maintenance or replacement;
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
means of lifting for removal or dismantling of equipment;

size of the wet well(s) and, where applicable, the dry well;

inlet configuration;

welfare facilities for staff where required;

power source for drive units (e.g. electricity or diesel) and if necessary, standby power source;

fuel storage capacity, where appropriate;

over-pumping facilities;

susceptibility to vandalism.
The layout shall also:

allow pumps to be installed so they can be primed;

keep the suction pipelines substantially horizontal, as short as possible and with no areas for air to
become trapped;

ensure that non-immersible electrical and mechanical equipment is protected from flooding.
Where possible control equipment should be in the same location.
The hydraulic design of the pumping station and rising main shall be considered together.
Buildings and chambers shall be adequately ventilated to avoid build-up of toxic or explosive gases. Wet wells
shall be provided with forced ventilation where necessary. Gas testing facilities shall be made available (either
portable or permanently installed).
F.3.2 Wet well design
The wet well should be designed so that:

sump extends below the level of incoming sewers;

it is possible to isolate, empty and clean the wet well (e.g. by partitioning or duplicating the wet well);

"dead zones" where sedimentation can build up are avoided (in some cases model testing could be
useful);

intake configuration ensures stable flow conditions to the pump, particularly avoiding air entrainment (in
some cases model testing could be useful);

there is adequate clearance between the base and sides of the wet well and the pump inlet;

it is protected against septicity (see 9.5.3);

any necessary measures to guard against explosion are taken.
The size of the wet well and its detailed design shall be determined from the maximum and minimum flow
rates. The capacity between start and cut out shall be set to limit the frequency of switching to within the drive
unit manufacturer's recommendations. Start levels shall give adequate wastewater levels to allow pumps to
prime.
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F.3.3 External layout and access
Access and appropriate parking shall be provided at all times for emergency vehicles, maintenance vehicles
and ancillary equipment. Adverse weather conditions shall be considered. The site shall be designed to deter
unauthorised access.
Adequate protection against lightning shall be provided.
F.3.4 Environmental impact
The design of the pumping station shall take into account its effect on the environment including:

consequences of discharges from combined sewer overflows;

noise, vibration and odour inside and outside the pumping station;

consequences of failure;

visual impact.
The national or local regulations or relevant authority can lay down requirements pertaining to the quality,
quantity and frequency of discharges to receiving waters (see 8.5.2 and 9.5.2).
Where emergency overflows are provided they shall be designed to ensure maximum retention of solids.
F.3.5 Structural design
The structural design of chambers and buildings shall be designed in accordance with EN 1990 to EN 1999 if
applicable or otherwise in accordance with relevant product standards and shall take account of:

structural integrity (taking into account loads from lifting equipment and seismic loadings where
appropriate);

watertightness;

prevention of floatation;

bearing capacity and chemical nature of the soil;

aggressive, corrosive and/or erosive effluents;

possible differential settlement between the structure and all incoming sewers and outgoing rising mains
and other services;

requirements of the national or local regulations or relevant authority.
F.3.6 Maintenance considerations
Mechanical and electrical equipment shall be selected which is robust and reliable and shall require minimal
maintenance. Consideration should also be given to the availability of spare parts.
The provision of appropriate lifting hoists and beams, and of lifting eyes or similar features on heavy
equipment, shall be considered.
Complete sets of current general arrangement and sectional drawings, operational, maintenance and service
manuals, circuit diagrams and parts lists shall be supplied and be available at all times.
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F.4 Design of rising mains
F.4.1 Principal considerations
The principal design considerations for rising mains for sewers include:

choice of a route;

choice of diameter;

positive and negative pressures and external loads;

choice of materials;

thrust;

discharge points;

control of septicity;

valve chambers;

whole life cost.
The hydraulic design of the rising main and pumping station shall be considered together. Methods for
calculation of head losses and flows in pipes are described in E.2.
F.4.2 Choice of route
Where possible the route should avoid pipeline summits and valleys.
The location of rising mains shall take account of the requirements for access for maintenance and operations.
Flushing or rodding connections may be incorporated.
Appropriate vehicular access shall be provided to valve chambers for operations and maintenance purposes
(see F.4.9).
F.4.3 Choice of diameter
The diameter of the rising mains shall be selected by considering:

design flow rates and associated velocities and pumping costs;

capital cost;

minimum velocities to limit sedimentation;

minimum diameter to limit clogging;

septicity implications of retention time.
F.4.4 Pressures and external loads
Pipelines shall be designed for pressure resulting from maximum flow, no flow and transient pressures
(positive or negative), also taking account of external loads. In the case of transient conditions, the amplitude
and frequency shall be estimated.
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Surge analysis shall be carried out taking into account all possible operating conditions. Numerous methods to
reduce or suppress surge are available.
F.4.5 Choice of materials
The material for the rising main shall be selected in accordance with the principles in 8.6.4. Particular care
shall be taken:

where wastewater contains aggressive substances;

in contaminated or aggressive soil conditions;

in adverse ground conditions;

in difficult terrain;

in aquifer protection zones.
F.4.6 Thrust
Thrust forces occur at valves, changes in direction and diameter, branches and blank ends and shall be
contained. The methods available include:

restrained joints over an adequate length of pipeline;

thrust or anchor blocks;

cradles and clamps, generally for non-buried pipelines.
Anchorages should be designed to avoid transmitting vibration.
Where thrust or anchor blocks are to bear against the soil, the safe bearing pressures shall be determined.
The possibility of shear failure, sliding, and potential disturbance of the block by subsequent excavation shall
be considered.
F.4.7 Discharge points
Discharge points shall be designed to minimise splashing and noise. Manholes into which rising mains
discharge shall be well ventilated having regard to the need for odour control.
Receiving manholes shall be protected against chemical attack and erosion where appropriate.
F.4.8 Control of Septicity
Septicity should be limited (see 9.5.3).
F.4.9 Valve chambers
Valve chambers shall be provided where necessary to allow maintenance of valves. The design of valve
chambers shall include for:

removal and replacement of valves;

safe access for personnel into the chamber;

vehicle access to the site of the chamber.
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Arrangements shall be made for removing standing water from the valve chambers.
Air valve chambers shall be adequately ventilated.
F.5 Components and appliances
F.5.1 Pumps
Each pump and its drive unit shall be suitable for the nature and composition of the wastewater to be pumped
and for duty throughout the specified range of station requirements such as flow rates, heads and duty points.
In some cases it could be necessary to modify the pumping station design to find an acceptable combination
of pump and pumping station to avoid:

overloading of pumps, leading to abnormal increase in power consumption;

cavitation throughout the permissible range of operating speeds, flows and available suction level;

negative suction head.
In addition to any testing carried out before delivery, pumps shall be tested after installation for compliance
with user requirements. Performance tests for acceptance shall be agreed with the pump supplier.
Further factors to be considered shall include:

optimisation of efficiency;

anticipated future flows taking into consideration the design life of the pump;

pump speed (fixed speed, multi-speed or variable speed);

materials used in pump construction, including susceptibility to corrosion and erosion;

ability to pass permitted solids without clogging.
F.5.2 Prime Movers and Drives
Prime movers and drives shall be suitable for the types of pump selected and rated for all the operational
conditions. They shall be designed to be energy efficient.
Where electric motors are to be in contact with potentially explosive atmospheres, they shall be explosion
proof.
All non-submersible plant shall be located in a machinery room which is protected from flooding.
Types of prime movers which may be used include:

electric motors;

internal combustion engines.
These may be multiple or variable speed prime movers.
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EN 752:2008 (E)
Types of drive which may be used are:

direct;

geared;

belt;

close coupled;

intermediate shafting.
Vibration shall be minimised taking into account any requirements of national or local regulations or the
relevant authority.
F.5.3 Valves
Valves of varying types may be required as follows:

isolating valves to allow sections of pipework, pumps, valves etc. to be removed without emptying the
whole rising main;

washout valves at low or intermediate points to allow sections of the rising main to be emptied;

non-return valves at pumps to prevent backflow from the rising main;

air valves at summits and other points indicated by the surge analysis. When a single valve is used this
shall be double acting.
When fully open valves should not disturb the flow distribution. Consideration shall be given to the surge
effects of valve operation.
To minimise surge pressures in the rising mains, valves on rising mains may be arranged to close before
pumps are stopped, and to open after they have reached full speed, both at controlled rates.
All valves shall be suitable for use with wastewater and shall be designed to prevent retention of solids.
All valves shall be identified by durable tags.
F.5.4 Controls and electrical equipment
All electrical installations shall meet the requirements of national or local regulations or the relevant authority
and, where appropriate, shall be protected by suitable enclosures (e.g. drip proof, explosion proof). High
voltage equipment shall be secure from access by unauthorised personnel. All electrical equipment shall be
properly earthed and protected from lightning damage.
Switchboards and motor control centres should be of modular construction. Each circuit should be totally
segregated. Each pump set shall be provided with a separate starter. Safeguards shall be incorporated in
pump controls to stop units in the event of loss of suction pressure or unacceptable flow conditions. Control
systems shall ensure that unnecessary repeated stopping and starting or speed changes are avoided.
Controls may use various devices to activate the closing of the electrical circuit e.g. floats, electrodes,
ultrasonic's, pressure transducers, time controls. Control systems should allow for the switching sequences to
be varied, where two or more pumps are used in parallel or to change from a normal duty pump to the standby
pump.
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A separate connection point for a temporary power generator, with switching arrangements, should be
considered.
F.5.5 Instrumentation
Suitable instrumentation shall be provided. This can include:

monitoring equipment (e.g. level, flow, pressure, speed, voltage, current, power factor, gas content, hours
run etc.);

indication of operation of duty/standby pumps.
Information, alarms, and instructions can be relayed by telemetry to or from a remote location. The design of
telemetry systems shall consider present and future data requirements and the means of data transmission.
F.5.6 Alarms
Provision of alarms shall be considered, these can include:

flammable gas;

fire;

high water level;

bearing temperature;

motor temperature;

pump failure;

power failure;

vandalism.
An alarm system should have an emergency power source capable of operating for at least 24 h in the event
of failure of the main power supply.
Alarms should be relayed by telemetry to a central location.
F.6 Health and Safety
The principles for occupational health and safety set out in clause 7 should be applied to the design,
construction and operation of pumping stations. Adequate welfare and first aid facilities should be provided.
National or local requirements can also apply. The principal risks to be addressed arise from:

work in a confined space;

work in a wet and poorly illuminated location;

falls from height;

potentially explosive, oxygen deficient or toxic atmosphere;

fire;
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
moving machinery;

noise and vibration;

electrical installations;

biological contaminants;

liquid filled tanks;

remote working;

alarm systems (see F.5.6).
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EN 752:2008 (E)
Bibliography
[1]
EN 773:1999, General requirements for components used in hydraulically pressurized discharge pipes,
drains and sewers
[2]
EN 1293:1999, General requirements for components used in pneumatically pressurized discharge
pipes, drains and sewers
[3]
EN 13380:2001, General requirements for components used for renovation and repair of drain and
sewer systems outside buildings
[4]
EN 13689:2002, Guidance on the classification and design of plastics piping systems used for
renovation
[5]
EN ISO 9000:2005, Quality management systems - Fundamentals and vocabulary (ISO 9000:2005)
[6]
EN ISO 9001:2000, Quality management systems - Requirements (ISO 9001:2000)
[7]
EN ISO 9004:2000, Quality management systems - Guidelines for performance improvements (ISO
9004:2000)
[8]
EN 14457:2004. General requirements for components specifically designed for use in trenchless
construction of drains and sewers
[9]
EN 1085:2007, Wastewater treatment — Vocabulary
[10]
EN 12056-4, Gravity drainage systems inside buildings — Part 4: Wastewater lifting plants, Layout and
calculation
[11]
EN 1091, Vacuum sewerage systems outside buildings
[12]
EN 1671, Pressure sewerage systems outside buildings
[13]
EN 12056-2, Gravity drainage systems inside buildings — Part 2: Sanitary pipework, layout and
calculation
[14]
EN 13508-1, Condition of drain and sewer systems outside buildings — Part 1: General Requirements
110
BS EN 752:2008
National Annex NA
(informative)
Guidance for the use of BS EN 752:2008 in the UK
NA.1 Introduction
This National Annex gives additional information about practice to assist users in the application of
EN 752 in the United Kingdom. The numbers in brackets after the headings are the corresponding sub
clause numbers in the text of the European Standard.
Further information on the requirements of Sewerage Undertakers for sewers and lateral drains that
are to be adopted can be found in Sewers for Adoption [1] or Sewers for Scotland [2], as appropriate.
For other drains and sewers, Building Regulations will apply. Information on the requirements of
Building Regulations can be found in Approved Document H [3] (for England and Wales), the Technical
Handbooks to the Building Standards (Scotland) Regulations [4], [5] (in Scotland) or the Technical
Booklet H to the Building (Northern Ireland) Regulations [6].
NA.2 Hydraulic design of foul drains and sewers (8.4.2 and 9.4.2)
NA.2.1 Calculation of design foul wastewater flows
NA.2.1.1 General
There are two methods of determining foul wastewater flows in pipes:
a)
the probability method (see NA.2.1.2), based upon the flow rates and probability of discharge of
sanitary appliances;
b) the population method (see NA.2.1.3), based upon population served.
The probability method is mainly used for drainage adjacent to buildings.
It should be noted that the two methods will give different results. Generally, the population method
should be used where the probability method indicates that pipe sizes of greater than DN 150 are
required.
NA.2.1.2 Drain systems
Foul wastewater flow in small drainage systems is intermittent even in systems serving a large number
of appliances. It is normally of a wave form, close to the point of connection of a discharge stack, or
an appliance, especially a WC. As the wave travels along the drain, its velocity and depth decrease,
the attenuation depending on the volume of flow, the gradient, the bore, the hydraulic roughness of
the drain and the presence of fittings. It can also be affected by simultaneous discharges from other
appliances connected to the system.
Probability theory is used to estimate the maximum peak flow rate from appliances and flow through
the drain is assumed to be steady, without attenuation. This ensures that the pipe sizes are adequate
at positions of maximum flow depth. Some oversizing downstream of connections in systems with long
pipe runs can result but this is usually acceptable as it provides a factor of safety and can enable future
connections to be made without causing surcharge.
1
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BS EN 752:2008
Clause 9.4.2 requires that the design foul wastewater flow rate should be determined by using the
method described in EN 12056-2. System Type III is usually used in the UK.
For the design of drains and sewers serving small numbers of dwellings, where the numbers and types
of appliances are not known, a value of 3,0 discharge units per dwelling should be used, subject to a
minimum flow of 1,6 l/s. When using this method pipes should be sized to give a maximum depth of
flow of about 0,7 DN in order to allow ventilation of the drains.
Clause 9.4.2 requires that design trade effluent flows are calculated separately and are added to the
foul wastewater flows.
Generally, no allowance for infiltration is made in this method. However, an allowance for infiltration
may be added to the calculated flows if the designer considers this necessary.
NA.2.1.3 Sewer systems
In sewers where there is a continuous flow for much of the day, domestic foul wastewater flow rates
generally estimated on the basis of a flow rate per capita per day. Peak foul wastewater flow rates are
higher than the average flow rates. These are estimated by multiplying the average daily flow rates by
a peaking factor. In the UK, a peaking factor of up to six times the domestic flow rate is typically used
depending on the size of the catchment area. In addition, an allowance is made for infiltration.
For sewers where flow is not continuous, such as those serving small developments or at the head of
larger systems, the probability method described in NA.2.1.2 should be used.
For the design of adoptable sewers for new housing developments Sewerage Undertakers [1] usually
specify a design flow of 4 000 litres per dwelling per day. This approximates to 200 litres per person per
day for a population of 3 persons per dwelling with a peaking factor of 6 plus a 10 % allowance for
infiltration.
For non-domestic buildings, the design flow should be calculated using the probability method for
those parts of the network where these flows are likely to be a significant part. Otherwise, per capita
flow figures may be used where these are available.
In the absence of specific data, design flows for trade effluents should be based on information on
water usage and effluent discharges for similar industrial buildings. In the absence of such information,
a value of 0,5 litres per second per hectare should be used for normal industry usage or 1,0 litres per
second per hectare for heavy usage [1], [2].
NA.3 Flow capacity of pipelines (8.4.2 and 9.4.5)
NA.3.1 Pipeline headlosses
NA.3.1.1 General
The Colebrook-White equation (see annex E, equation E.1) is generally used for design in the UK. Tables
giving the solution of the Colebrook-White equations for a range of pipe sizes, hydraulic pipeline
roughness values and pipe gradients are available [7]. Values of the hydraulic pipeline roughness (k)
commonly used with this equation are given below.
Whilst in theory the roughness is related to the height of the roughness elements of the pipe wall, in
practice it is also influenced by other factors; these comprise the straightness of the pipe, discontinuities
at the joints, free water surface at part-full flow, slime growths around the internal perimeter, grease
build up and sediment deposits.
2
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BS EN 752:2008
NA.3.1.2 Foul and combined drains and sewers
In pipes carrying foul sewage, the roughness will be influenced to some extent by the pipe material but
will be primarily dependent on the slime that grows on the inside surface of the pipe below the water
level corresponding to the maximum daily discharge.
Recommended roughness (k) values for foul and combined drains and sewers in average conditions are
given in Table NA.1.
Table NA.1 — Recommended roughness values for pipe full and combined drains and sewers
Recommended
Values of k
[mm]
Peak DWF* velocity typically exceeds 1,0 m/s
Peak DWF velocity between 0,76 m/s and 1,0 m/s
0,6
1,5
* Peak DWF = Dry weather flow diurnal maximum = 2 × DWF
where DWF is the average daily dry weather flow
Hydraulic pipeline roughness values for brick sewers will depend on the condition of the brickwork as
well as sliming and debris. Guidance on hydraulic pipeline roughness values for brick sewers is given in
the SRM [8].
Although a pressure main carrying sewage will slime, the amount and pattern of sliming will be
different from that occurring in a gravity foul sewer. Further guidance is given in published tables [7].
NA.3.1.3 Surface water drains and sewers
A surface water drain or sewer is unlikely to slime to any significant extent, but it is likely to contain
deposits of grit. For design of surface water drains and sewers, a certain amount of deposits are assumed
and a hydraulic pipeline roughness (k) of 0,6 mm is therefore generally used regardless of the material.
Exceptionally, where surface water drains and sewers will remain clean, unsoiled, and in good condition
throughout their design life, the roughness will depend principally on the material. In such cases,
recommended hydraulic pipeline roughness values (k) for pipes of different materials can be obtained
from published tables [7].
NA.3.2 Local headlosses
NA.3.2.1 General
Local headlosses are usually small in relation to the frictional losses and are not normally considered.
Where exceptionally local headlosses are considered, the following values for local headloss coefficients
(KL) are generally used, in conjunction with equation E.3 (see annex E).
NA.3.2.2 Manholes
NA.2 gives values of energy loss coefficient, KL, derived from experiments on manholes where the
sewer is surcharged. The energy losses when the sewer is only just full (i.e. with the flow confined by
the manhole benching) will be less than those obtained using these coefficients. Where the manhole
incorporates a junction, the energy losses will be increased and will depend on the geometry of the
junction and on the flows in the branches.
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Table NA.2 — Energy loss coefficient, KL, for manholes
Plan shape of
manhole
Rectangular
Circular
Type of manhole
Straight through
0,10
0,15
30° bend
0,40
0,50
60° bend
0,85
0,95
NA.3.2.3 Circular bends
Table NA.3 gives values of KL for 90° circular bends, flowing full, for various ratios of bend radius, R, to
nominal pipe bore, D.
Table NA.3 — Energy loss coefficient, KL, at bends
Bend radius/pipe diameter
R/D
0,5
1,0
1,5
2,0
5,0
10,0
KL
1,00
0,25
0,18
0,16
0,18
0,24
The values given in Table NA.3 only apply when the length of straight pipe downstream from the bend
is greater than 30 pipe diameters.
NA.3.2.4 Lobster-back bends
Figure NA.1 — Lobster-back bend
The energy loss coefficient, KL, for a single mitre bend is given by:
KL = 1,4 ×
a
90
where
a is the bend angle (in degrees).
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Table NA.4 gives the loss coefficient for a 90° lobster-back bend comprising four 22,5° mitre bends,
three 30° mitre bends, or two 45° mitre bends.
Table NA.4 — Energy loss coefficient, KL, for lobster-back bends
L/D
4/22,5°
3/30°
2/45°
Loss coefficient KL
0,5
1,5
3,0
6,0
0,40
0,25
0,32
0,32
0,45
0,30
0,35
0,37
0,55
0,40
0,48
0,50
NOTE 1 L is the centreline length of one of the individual short pieces of pipe (which are all of
equal length) from which the bend is made. D is the nominal pipe bore.
NOTE 2 The values given are for a rough pipe; the loss coefficients for a smooth pipe will be
approximately 75 % of these values.
NA.4 Surface water drains and sewers (8.2, 8.4.3 and 9.4.3)
NA.4.1 General
NA.4.1.1 Discharge of surface water
In England and Wales the Building Regulations [3] require that surface water is discharged in accordance
with the following order of precedence:
•
to an infiltration drainage system; or
•
where discharge to an infiltration drainage system is not reasonably practicable to a watercourse; or
•
where neither is reasonably practicable, to a sewer.
NOTE Sewerage Undertakers in England and Wales are not presently able to adopt all types of infiltration drainage
system. Further guidance on adoption can be found in the Interim Code of Practice for Sustainable Drainage Systems [9].
NA.4.1.2 Design of surface water drainage systems for new developments
The planning authority (see NA.13.10) with advice from the principal rivers and land drainage authority
(see NA.13.5) will usually require that the run-off from a new development (whether the development
is on land that has previously been developed or not) is as far as practicable similar to the run-off from
the site in its natural (undeveloped) state. They will also require a flood risk assessment showing how
the surface water from the site will be managed [10]. To achieve this, consideration should be given to
the use of Sustainable Drainage Systems (see NA.4.4). Methods for calculating greenfield run-off criteria
for a particular site can be found in Interim Code of Practice for Sustainable Drainage Systems [9].
Any surface water drains or sewers should be designed using an appropriate method. Methods based
on the Wallingford Procedure [11] are commonly used in the UK.
For new systems, an initial design should be undertaken using a simple design method such as the
Wallingford Modified Rational Method. Further information on this method can be found in NA.4.3
and in the ‘Wallingford Procedure’ volume 4 [11]. In such cases, drains and sewers should be designed
so that the pipes do not surcharge at the design rainfall frequencies given in NA.4.2.3.3.
For larger developments (e.g. sites with an area of more than 2 000 m2 and a length of drain or sewer of
more than 200 m) the initial design should be checked using an appropriate flow simulation method. The
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design should then be improved so that the design flooding frequency is not greater than 1 in 30 years
(a probability of flooding of 0,03 in any year).
During extremely wet weather, when the design criteria are exceeded, the capacity of the surface
water drains and sewers sometimes inadequately contain the flow in the pipes. To take account of
this, 8.4.3.3.requires the designer to undertake an exceedance flood risk assessment. The layout of the
development and the drains and sewers should be arranged such that the impact of any flooding is
minimized (see NA.4.5 and 8.4.3.3).
NA.4.1.3 Upgrading existing surface water drain and sewer systems
The performance of the existing surface water drain or sewer system should be analyzed using an
appropriate flow simulation method. Any parts of the system where the frequency of flooding is
unacceptable should then be upgraded so that the design flooding frequency is not more frequent
than 1 in 30 years (a probability of flooding of 0,03 in any year).
In view of the uncertainties in predicting surface water flows, consideration should be given to
increasing the design pipe sizes where this would not significantly impact on the cost.
NA.4.1.4 Combined drains and sewers
For combined systems, the drains and sewers should be sized to the same performance criteria as surface
sewers taking into account both the run-off and the foul wastewater flows and, where applicable,
consented discharges from combined sewer overflows in the system.
NA.4.2 Design rainfall
NA.4.2.1
Introduction
The design rainfall intensity depends on geographical location, rainfall frequency and duration.
A number of different types of design rainfall data are available. The type of data used will depend on
the type of design and the calculation methods being used. The types of data include:
•
flat rate rainfall;
•
catchment specific constant rate rainfall calculated from intensity duration frequency curves;
•
catchment specific synthetic rainfall profiles;
•
rainfall times series data.
In the UK, drains and sewers designed to cope with heavy summer rainfall events are generally adequate
to deal with melting snow.
NA.4.2.2 Flat rate rainfall
For design of small paved areas up to 4 000 m2, in situations where ponding can be tolerated during
heavy rainfall and for a few minutes afterwards, a flat rate rainfall of 0,014 l/s·m2 (approximately
50 mm/h) may be used.
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NA.4.2.3 Constant rate rainfall
NA.4.2.3.1 General
Where simple methods of calculating run-off described in 8.4.3.3 are used, constant rate rainfall
intensities are available. These are generally used for designs to give no surcharge in a specified “design
rainfall frequency” (see Table NA.5).
NA.4.2.3.2 Rainfall for design of drainage from paved areas
The design rainfall frequencies shown in Table NA.5 are recommended.
Table NA.5 — Recommended design rainfall frequencies for the design of paved areas
Risk category
Situation
Design rainfall frequency
Return period
(1 in “n” years)
Probability of
exceedance in any
one year
Category 1
Normal situations where ponding can
be tolerated during heavy rainfall and
for a few minutes afterwards
1
1
Category 2
Ponding cannot be tolerated
5
0,2
Category 3
(see Note a.)
Where a building or its contents
require additional protection
1,5 × design life of
building (see Note b.)
1/(1,5 × design life of the
building) – (see Note b.)
Category 4
(see Note a.)
Where a building or its contents
require a higher degree of security
than category 3
4,5 × design life of
building (see Note b.)
1/(4,5 × design life of the
building) – (see Note b.)
a. Categories 3 and 4 should only be used in exceptional circumstances.
b. Design rainfall intensities for other frequencies and durations can be calculated using the method
described in NA.4.2.3.3.
For the design of drainage for areas up to 4 000 m2 [3] rainfall event durations of 5 min are generally
used. Constant rate rainfall intensities for rainfall for various design rainfall frequencies for durations
of 5 min are given in Figure NA.2 to Figure NA.6.
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Figure NA.2 — Constant rate rainfall intensity for an event of 5 minutes’ duration
with a probability of exceedance of 1 in 1 year (a return period of 1 year)
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Figure NA.3 — Constant rate rainfall intensity for an event of 5 minutes’ duration
with a probability of exceedance of 0,2 in 1 year (a return period of 5 years)
Flat rate rainfall intensities for 5 minutes’ duration rainfall events with lower probabilities of exceedance
(longer return frequencies) are given in Figure NA.4 to Figure NA.5 for unusual situations where the
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drainage system is the sole line of defence against flooding (e.g. where a building would be flooded if
the system were to surcharge) – see NA.4.5.
Figure NA.4 — Constant rate rainfall intensity for an event of 5 minutes’ duration
with a probability of exceedance of 0,02 in 1 year (a return period of 50 years)
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Figure NA.5 — Constant rate rainfall intensity for an event of 5 minutes’ duration with
a probability of exceedance of 0,002 in 1 year (a return period of 500 years)
The maximum theoretical precipitation for any given location is estimated using a rainfall frequency
of 1 in 35 000 years. Figure NA.6 shows the maximum constant rate rainfall intensity for an event of
5 minutes’ duration.
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Figure NA.6 — Maximum constant rate rainfall intensity for an event of 5 minutes’ duration
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NA.4.2.3.3 Rainfall for design of drainage from larger areas
For the design of drainage for larger areas up to 200 ha or for times of concentration up to 15 min
using the same design method (see 8.4.3.3) site-specific rainfall data can be calculated for any point
in the UK using the Wallingford Procedure [11], [12], [13] (see NA.4.1.2) for a specified duration for a
specified design rainfall frequency.
The duration of the design rainfall event is taken to be equal to the time of concentration (tc ), which is
the shortest time in which all parts of the upstream catchment will contribute to the flow at the point
of calculation. This is given by the equation:
tc = te + tf
(NA.2)
where
te
is the time of entry – i.e. the time taken for rainfall landing on a surface to enter the drain or
sewer, and
tf
is the time of flow – i.e. the maximum time of flow in the drain or sewer from the furthest
point of entry to the pipe where the flow is being calculated.
The time of entry depends on the distance to the point of entry, the ground slope and the intensity of
the rainfall. A value of 5 min is commonly used.
Recommended design frequencies for use with this method are shown in Table NA.6.
Table NA.6 — Recommended design rainfall frequencies for use
with simple design methods on new developments
Type of site
Design rainfall frequency
Return period
(1 in “n” years)
Probability of
exceedance in any
one year
Sites with average ground slopes greater than 1 %
1
1
Sites with average ground slopes 1 % or less
2
0,5
Sites where the consequences of flooding are severe
(e.g. adjacent basement properties)
5
0,2
NA.4.2.4 Time-varying rainfall profiles
NA.4.2.4.1 General
Two main types of time-varying design rainfall events are available for the UK for use with sewer flow
simulation models:
•
synthetic design rainfall events having an idealized single peaked symmetrical profile;
•
rainfall time series that are made up of real or simulated single or multi-peaked rainfall events.
NA.4.2.4.2 Synthetic rainfall profiles
Where sewer flow simulation methods are being used to design drain and sewer systems design
rainfall events of specified frequencies from 1 in 1 year (a probability of exceedance in one year of 1)
upwards and specified durations can be determined from intensity-duration-frequency curves using
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the Wallingford Procedure [11], [12], [13]. These profiles are symmetrical with a single peak and are
built into some standard flow simulation packages available in the UK.
This type of rainfall data may be used to design new sewer systems as well as to simulate existing
systems in order to assess performance. The critical duration used for any part of the system should
be determined by experiment. Different rainfall event durations can be appropriate when designing
different parts of some systems, particularly where the system incorporates detention tanks.
NA.4.2.4.3 Rainfall time series
An alternative to synthetic idealized profiles with sewer flow simulation methods is to use events
selected from long series of historic rainfall data. This method is particularly suitable for use when
considering the environmental impact of discharges from outfalls and combined sewer overflows. This
type of data can also be more suitable for simulation of detention tanks.
Historic series of significant duration data are available for comparatively few sites in the UK. Much
of this data is only available for time increments of 1 h, which is not generally suitable for detail
sewer flow simulation models. Disaggregation is, however, available from a number of sources that
can produce simulated 5-minute increment data from hourly values. Details of historic rainfall data
available can be obtained from the Meteorological Office.
Where historic rainfall series are not available, software is now available from a number of sources for
the generation of synthetic rainfall time series for locations in the UK.
NA.4.3 Methods of calculating run-off from small development schemes
Annex E.3 contains a simple method of calculating flows from small developments based on equation E.7
as follows:
(NA.3)
Q = CiA
The Wallingford Procedure [11], [13] contains a modified version of this equation that is commonly
used in the UK in which the run-off coefficient C is calculated from equation NA.3.
(NA.4)
C = Cv C R
Where
Cv
is the volumetric run-off coefficient that is defined as the volume of rainfall in the system
that becomes surface water in the drain or sewer system. This can be calculated from the
Wallingford percentage run-off equation [11] as follows:
Cv =
0,829PIMP + 25SOIL + 0,078UCWI − 20,7
100
(NA.5)
Where
PIMP is the percentage of the surface area contributing to the run-off that is impermeable,
SOIL
is an index between 0,15 and 0,5 depending on the Winter Rainfall Acceptance Potential
(WRAP) Class of the soil [11], [12],
UCWI is the design urban catchment wetness index as defined in the Wallingford Procedure [11],
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typical values of Cv are between 0,6 for catchments on very pervious soils to about 0,9 on
catchments with heavy clay soils. An average value of 0,75 is typically used,
and
ψR is a routing coefficient that varies with the shape of the catchment and the peakedness of
the rainfall event. The Wallingford Procedure [11], [13], recommends a value of 1,3 for use
in the UK.
A typical value of C is therefore 0,75 × 1,3 = 1,0. Equation E.7 in annex E therefore becomes:
Q = iA
(NA.6)
For the design of paved car parks, roads and footpaths, the effective catchment area is typically taken
to be equal to the plan area of the paved area plus the effective area of any sloping or vertical surface
that drains on to it and the run-off coefficient, C, in annex E table E.3 is generally taken as 1,0.
NA.4.4 Sustainable drainage systems (SUDS) (8.4.3 and 9.4.3)
NA.4.4.1 Introduction
SUDS use a variety of techniques to manage surface water in a more environmentally sustainable
fashion than some conventional techniques. These techniques largely involve flow attenuation or a
mixture of infiltration drainage and flow attenuation techniques.
NA.4.4.2 Flow attenuation
Flow attenuation can be achieved either:
•
online, in which case the sewage flows through the attenuation device in dry weather; or
•
offline, in which case the flow is spilled into the device only in times of high flow.
The volume of storage required should be calculated from a consideration of the inflow and outflow
hydrographs based on an appropriate design rainfall event (see NA.4.2).
Closed attenuation devices can also be used to manage flows in existing combined or surface water
sewer systems.
NA.4.4.3 Infiltration drainage
NA.4.4.3.1 Introduction
Under certain circumstances infiltration drainage systems can be used to dispose of surface water. They
can be sized to cope with an expected rainfall event with or without overflowing.
If surface water drainage is to be discharged to an infiltration drainage system, the subsoil and the
general level of the ground water should be investigated.
Infiltration drainage systems dispose of surface water by allowing the surface water to infiltrate into
the soil over a period of time. The water pollution control authority (see NA.13.4) will usually require
that any discharge is made to the unsaturated zone above the groundwater table and not directly to
the groundwater table itself. Detention storage is provided to store the peak flows during heavy rainfall
allowing it to infiltrate into the ground when the flow has reduced. The volume of storage required
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therefore depends on the hydraulic properties of the soil, the area which the system is draining, the
topography and the chosen design rainfall events.
In some cases, an overflow is provided from the infiltration drainage system either to a surface water
sewer of direct to a surface receiving water.
In order to limit any possible alteration to the quality of groundwater, attention should be paid to the
source of the run-off water that is to be collected. In particular, the water pollution control authority
(see NA.13.4) is unlikely to permit infiltration drainage where:
•
the site is close to a groundwater abstraction point (e.g. in groundwater source protection zone 1
(the inner zone). Information on the location of these zones in England is available from the water
pollution control authority [14] (see NA.13.4);
•
the risk of contaminated run-off is high (e.g. hard standing and car parking in industrial areas and
lorry parking);
•
there is a risk of groundwater contamination due to leaching of contaminants from the soil.
If there is any doubt as to whether any of these conditions arise and for any major infiltration drainage
(e.g. > 1 ha) scheme, advice should be sought from the water pollution control authority (see NA.13.4).
However, in other cases where the risk of contamination is low (e.g. roof drainage and residential or
retail car parking areas), infiltration drainage can usually be used.
NA.4.4.3.2 Site investigation
Where any doubt exists as to the suitability of the ground, it can be necessary to obtain permeability
figures by test. CIRIA Report 156 [15] and BRE Digest 365 [16] describe a comprehensive test for the
measurement of the soil infiltration rate. On some sites, the permeability is substantially reduced when
the soil is saturated. If this applies, the testing should be carried out in saturated conditions. In other
situations (e.g. chalk valleys), there is a high fluctuation in groundwater levels. In such cases the design
should take into account the historic peak groundwater levels.
NA.4.4.3.3 Design
Depending on the type of infiltration system being considered the design may be on the basis of:
•
infiltration through the base of the system only;
•
infiltration through the sides of the system only;
•
infiltration through both the base and sides of the system.
Detailed guidance on the design of infiltration drainage systems is given in CIRIA Report 156 [15].
BRE Digest 365 [16] describes in detail how to design soakaways. This iterative design method is also
available on computer disk.
NA.4.4.3.4 Access
Below ground infiltration drainage systems should be designed with facilities for inspection and
maintenance. The life of an infiltration drainage system will be reduced if its flow paths become
clogged by silt or debris.
NA.4.4.3.5 Proximity to buildings
Soils can be affected in various ways by the action of water. It is not desirable to site an infiltration
drainage system in any position where the ground below foundations is likely to be adversely affected.
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In particular, a below-ground infiltration system that concentrates significant volumes of water in a
small area (e.g. soakaways) could damage vulnerable foundations by:
•
localized differential movement of shrinkable clay soils under the foundations;
•
dissolution of certain rocks under foundations;
•
collapse of certain open-textured, wind-blown soils in the presence of water leading to voids under
foundations;
•
reduced strength of certain types of soil in the presence of water.
If there is a risk of any of these conditions then specialist geotechnical advice should be obtained.
The infiltration of surface water into the ground over a large area at rates similar to those that existed
when the land was in its undeveloped state do not normally cause problems unless there are specific
geological hazards.
NA.4.4.4 Detention tanks and tank sewers
The volume of storage and the limiting rate of discharge downstream for detention tanks and tank
sewers on combined and partially separate systems are generally designed using sewer flow simulation
models (see 8.4.3.3 and Annex E) to achieve specified design rainfall frequencies. These should use
either synthetic design rainfall events of the most onerous duration (this can be more than four times
the time of concentration), using rainfall time series (see NA.4.2), or a combination of both methods.
Where a tank is being installed on a drain or sewer that is connected to an existing sewer system, the
relevant authority should be consulted to ensure that the tank and its control device do not lead to
flooding (either on the proposed drain or elsewhere) outside the design limits.
The tank should be adequately ventilated.
The base of the tank should be designed to minimize the build-up of sediments. This can be done by
provision of benching and channels with sufficient gradient or by use of active sediment removal systems
using flushing, scraping or sprays. Further guidance on the design of tanks to minimize sedimentation
is given in Detention tank design and maintenance [17].
NA.4.4.5 Flood storage ponds
Flood storage ponds can be either wet ponds, which permanently contain water, or dry ponds, which
are filled only intermittently.
Where the system discharges into a watercourse, the maximum discharge downstream is generally
specified by the rivers and land drainage authority (see NA.13.5). Where the system discharges into
a sewer system, the maximum discharge will generally be specified by the sewerage undertaker or
highway authority (for highway drainage systems) as appropriate (see NA.13.8).
The volume of storage may be calculated using sewer flow simulation methods (see above) or other
methods. Detailed advice on all aspects of design is given in “The design of flood storage reservoirs” [18].
NA.4.4.6 Permeable pavements
These systems are predominantly flat and their shape is commonly such that there is little storage per
unit of infiltration area. A layer of fill material underlying the surfacing, is therefore generally used
to provide storage during a rainfall event. Depending upon the nature of the fill and the overlying
surface material, a filter or geotextile is sometimes used to separate the materials. Although they are
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mainly used to dispose of just the rainfall falling into the surface itself, they can also be used to dispose
of water from the roofs of adjacent buildings and paved areas.
The systems can be porous (i.e. where the water drains through voids that are integral to the pavement
material) or permeable (i.e. where the solid parts of pavement are impermeable but the water drains
through voids between the solid parts of the pavement).
Permeable pavements will usually require maintenance of their surface. Porous pavements will usually
require periodic cleaning to maintain infiltration rates.
Detailed design guidance is given in CIRIA Report C582 [19].
NA.4.4.7 Infiltration basins and swales
An infiltration basin is a depression or an area of land surrounded by a bank or berm, which detains
surface water until it has infiltrated through the base and/or sides of the basin. Infiltration basins are
sometimes also referred to as dry retention ponds.
A swale is a grass-lined channel with shallow side-slopes that is used both to convey and to infiltrate
run-off. To increase the infiltration and detention capacity of swales, they can be provided with low
check dams across their width. At the end of the swale, there is usually an outfall to discharge excess
flows to a surface receiving water.
Infiltration basins and swales can improve the quality of the run-off. In well-designed systems the
improvement in water quality can be substantial.
Detailed design guidance is given in CIRIA Report 697 [20].
NA.4.4.8 Pit soakaways
A pit soakaway consists of a pit from which water can infiltrate into the surrounding ground. Small
pits can be unlined and filled with hardcore, larger pits can be unfilled but lined, e.g. with brickwork
laid dry, jointed honeycomb brickwork, perforated precast concrete rings or segments laid dry, and the
lining surrounded with suitable granular material. An unfilled pit should be safely roofed and provided
with access for maintenance purposes. Although square or circular pits are compact, it is often easier,
and cheaper, to excavate trench soakaways if excavating equipment is available.
Provision should be made to remove sediments from the incoming flow to prevent the flow paths in
the surrounding soil from becoming clogged.
A soakaway can be used most effectively in pervious subsoils, such as graveI, sand, chalk or fissured
rock, and where it is completely above the water table. Seasonal variations in the water table can
necessitate an increase in the storage capacity.
In ground with low permeability where soakaways are a feasible solution, storage capacity should
be provided to retain the flows during prolonged or heavy rainfall (e.g. a capacity equal to 20 mm
of rainfall over the area being drained should be adopted). Its effective depth is measured below the
invert of the lowest incoming drain. This can be achieved by the provision of one soakaway or splitting
flow to a number of soakaways linked at overflow level by piped seepage trenches. Similar trenches
can be used to provide means of overflow from a soakaway.
Access points will enable the point of discharge of the drain to be viewed. For small filled soakaways,
a 225 mm perforated pipe can be used as an inspection well.
Detailed design guidance is given in CIRIA report 156 [15] and BRE Digest 365 [16].
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NA.4.4.9 Infiltration trenches
An infiltration trench is usually filled with permeable granular material, designed to promote infiltration
of surface water to the ground following convenient contours.
This type of soakaway provides better infiltration characteristics for a given excavation volume than
traditional soakaways.
Infiltration trenches should have at least two inspection access points, one at each end of a straight
trench. These should be linked, near the top of the granular fill, by a horizontal perforated or porous
distributor pipe. Where more than one drain feeds an infiltration trench, each connection should be
via a suitable access chamber.
With infiltration trenches, the use of catch pits at drain outlets and the use of T-piece inlets to the
perforated or porous distributor pipes will improve performance by limiting the sediment that could
otherwise block the distributor pipe.
Detailed design guidance is given in CIRIA report 156 [15].
Figure NA.7 — A T-piece inlet to an infiltration trench
NA.4.5 Exceedance flood risk assessment (8.4.3)
NA.4.5.1 Introduction
Traditionally surface water systems have been designed wholly as minor drainage systems in which
the flow is contained within the pipes. When the flow in the drainage system exceeds the capacity
of the minor system then the major drainage system will come into use. The major drainage system
is the system of formal and informal above ground flood pathways, including open and culverted
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watercourses and dry rivers. The interaction between the minor and major drainage systems is complex
and can be difficult to assess accurately.
An exceedance flood risk assessment (EFRA) is an assessment of the risk of a site or an area being
affected by flow that cannot be contained within the minor drainage system and the impact that any
changes made to these sites or areas will have on the exceedance flood risk.
NA.4.5.2 Flooding from minor systems
Flooding can also occur where a property, or part of a property such as a cellar, lies below the level of
the hydraulic gradient in the drainage system. This can only occur if there is a pathway between the
drainage system and the property. This does not have to be an actual pipe connection. Properties with
basements are particularly vulnerable to this form of flooding.
Above ground flow (exceedance flow) can be generated from four sources.
a)
flooding from manholes and other connections to the minor system as a result of lack of capacity
in the minor drainage system, or blockage, collapse or other service defects;
b) excess surface run-off that cannot enter the minor system due to the limited capacity of drainage
inlets;
c)
surface run-off from unpaved areas (e.g. land made impermeable by drought or ice, or by saturation
following prolonged rainfall);
d) flooding caused by high levels in receiving waters preventing drain or sewer systems from
discharging effectively.
NA.4.5.3 Flood pathways
NA.4.5.3.1 Introduction
Flood pathways convey exceedance flow from the point of origin. These pathways can take the form
of roads, paths or depressions in the surface or watercourses. The design of flood pathways will
considerably affect property flood risk.
Flood pathways can transfer the flow over significant distances, so that flooding can occur at locations
remote from the original point of discharge. This is particularly important in areas with a high
consequence of flooding. Flood pathways can be either natural or designed.
NA.4.5.3.2 Designed pathways
Flood pathways should be designed to convey the expected flow to a surface receiving water with
adequate flow capacity. The pathways should follow the natural topography a far as practicable and
should avoid buildings and other vulnerable infrastructure. Conveyance capacity can be significantly
influenced by details such as the height of kerbs. Safeguards should be put in place to ensure the
continued availability of the flood pathway, e.g. by preventing the construction of any barrier across
the pathway that could affect its efficiency.
Where practicable, the flood pathways should have another compatible primary function. Highways,
footpaths, car parks, ditches, swales and other vegetated areas can be used as flood pathways.
The depths and velocities of flow and the rate of rise in flow and depth should be limited so as not to
pose undue risk to their primary function, property nor to the public. The design should minimize the
accumulation of deep water in low spots unless it is designed as storage. An allowance should also be
made for wave action and uncertainties in the design flow. The public should also be made aware that
the area can flood.
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The design should seek to minimize the possibility of sediments or debris accumulated during extreme
events hindering the correct operation of the flood pathway. Arrangements should be made to inspect
and remove any debris arising from the use of flow paths.
In areas of significant redevelopment, the design of flood pathways should be considered in the same
way as those for new developments, including the use of natural drainage pathways and sympathetic
design of building layout to accommodate them.
The design of flood pathways is difficult in existing developments due to the restrictions of existing
building layouts in urban areas. Where it is not possible to limit the risk to property by use of flood
pathways, consideration should be given to increasing the design capacity of the minor drainage system.
NA.4.5.4 Surface storage
Surface storage can be included in the design of flood pathways to reduce peak flows by utilizing areas
that are used for other purposes for most of the time, e.g. playing fields can often be used as flood
storage ponds in extreme events.
The following issues should be considered during the design of surface storage areas:
a)
the depth of storage required to accommodate the flooding volume;
b) the length of time taken for the area to drain after the event;
c)
how the temporary storage of flood volume will affect the primary use of the area;
d) any damage or important loss of use that can occur as a result of using the area for surface storage;
e)
the risks to public health or safety caused by standing water.
NA.4.5.5 Calculating exceedance flow
The level of complexity required in calculating the flow, depth, velocity, volume and duration and
exceedance flow should match the needs of a particular project. In some cases, a low-level approximate
method can be justified whereas in others, e.g. where the risk and/or impact is higher, a high-level
detailed analysis will be necessary. The calculations could utilize detailed computer simulation models
or simple hand calculations. Guidance on calculations can be found in CIRIA C699 [21].
NA.4.5.6 Assessing the risk
Flood risk should be assessed using a combination of the probability of an event occurring and the
consequence of the event.
The amount of detail in the risk assessment undertaken should be appropriate to the size and complexity
of the area being assessed. There are three main groups of inputs that feed into the risk assessment
process:
a)
the determination of the exceedance flow, depth, velocity, volume and duration;
b) damage to property or the health and safety of the public;
c)
environmental and socio-economic impacts and the impact of the loss of the facility.
Guidance on risk assessment can be found in CIRIA report 699 [21].
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NA.5 Design of surface water inlets (8.4.3 and 9.4.3)
NA.5.1 Introduction
NA.5.1.1 General
This annex gives guidance on the drainage of surface water from paved areas, including the design of
inlets to gullies and linear drainage channels for minor roads (e.g. service and estate roads). Further
information is available in HR Wallingford Report SR533 [22] and Wallingford Report SR606 [23]. For
the design of all other roads, reference should be made to the Design Manual for Roads and Bridges
Volume 4 Section 2 [24], which is based on the work described in HR Wallingford Report SR533 [22].
Where a road is to be adopted, reference should also be made to any guidance produced by the
highway authority (see NA.13.8). It does not apply to paved areas at airports that are trafficked by
aircraft.
The number of inlets needed is often determined by the irregular shape of the areas between buildings,
rather than by the permissible area that can be drained to an inlet.
The drainage of paved areas can be achieved in a number of different ways:
•
provision of gullies set at low points within the paved area or individual sections of paved area that
drain directly to the below-ground drainage system (see NA.5.1.2). This is particularly suitable for
parking areas or other areas of hard standing on level ground;
•
provision of a channel or series of channels, usually formed in the paved surface or the paved surface
together with a kerb, that collect the run-off from the paved area discharging to the below-ground
drainage system through gullies situated at intermediate points along the channels and at their
downstream ends (see NA.5.1.3);
•
provision of linear drainage inlets that collect the run-off from the paved areas and discharge
directly to the below-ground drainage system (see NA.5.1.4);
•
drainage of run-off from the edge of the paved area to a permeable pavement, filter drain, filter
strip, or in some cases just directly onto adjacent land. This is particularly suitable for linear paved
areas such as footpaths or roads (see NA.5.1.5);
•
a permeable pavement (see NA.4.4.6);
•
a combination of the above.
The design of drainage of paved areas should take account of the run-off from any adjacent areas that
will discharge onto the paved area. Account should also be taken of the routing of any exceedance
flows (see NA.4.5).
Grit separation at gullies is usually provided by means of a gully pot. The retention of grit is a function
of the size of the gully pot and flow rate.
Where a gully or linear drainage channel discharges into a combined sewer or drain, a water-sealed
trap is necessary and such a trap is generally part of a gully pot. Traps may be omitted from individual
gullies that discharge into a drain or sewer used solely for the purpose of conveying rainwater.
For concrete paved areas, construction or expansion joints should not coincide with the lines of
collecting channels or cross areas in which ponding occurs at terminal gullies.
Gratings should comply with BS EN 124.
Gratings should be set flush or not more than 6 mm below the level of the paved area depending on
the expected settlement and surface use.
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BS EN 752:2008
To avoid damage by vehicles, gully gratings and frames should be properly bedded to give adequate
support against movement. The frame should be bedded using a good-quality mortar with a low water
content, on well-built brickwork or concrete. It is essential that sufficient time be allowed for the
bedding to develop its strength before a grating or frame is subjected to load. Gratings for linear
drainage channels should be fixed in accordance with the manufacturer’s instructions.
The design procedure for design of inlets is illustrated in Figure NA.8 and is described further in NA.5.1.2
to NA.5.1.5.
Gullies without
channels
Channels and gullies
Liner drainage
Drainage from edge of
paved area
Design layout and profile to limit the depth of flow over the paved area to acceptable levels (see NA.5.2)
Check gully capacity
(see NA.5.5)
Design gully capacity
and spacing (see
NA.5.6 or 5.7)
Design linear drainage
capacity (see NA.5.8)
Permeable pavement
Design pavement (see
NA.4.4.6)
Design filter strip or
filter drain (see NA.5.9)
Design piped system
Figure NA.8 — Principles of design of inlets
NA.5.1.2 Gullies without channels
Small paved areas can be drained to central terminal gullies. Larger areas can be split into panels each
with a central terminal gully. This is particularly useful in areas that are relatively flat. A typical layout
is shown in the inset to Figure NA.9.
The layout of the gullies and the profile of the paved area should be designed to limit the depth of
flow across the paved areas to acceptable limits (see NA.5.2) taking into account the flow rates (see
NA.5.4) and the capacity of the gullies (see NA.5.5).
NA.5.1.3 Channels and gullies
Larger paved areas can be more conveniently drained by means of collecting channels with intermediate
and terminal gullies.
The channels can be part of the paved surface itself, formed by the use of a kerb at the edge of the
paved surface or be purpose built channels. The layout of the channels and the profile of the paved
area should be designed to limit the depth of flow across the paved areas to acceptable limits (see
NA.5.2). An example of a typical layout of channels and gullies is shown in Figure NA.9.
The gully spacing along the channel should be designed to limit the width and depth of flow in the
channels to acceptable limits) taking into account the flow rates (see NA.5.4) and the capacity of the
gullies (see NA.5.6 or NA.5.7).
Gully gratings should be installed in collecting channels as close to the kerb as possible. For kerb inlet
gullies any struts or bars in the kerb inlet should not obstruct the flow.
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BS EN 752:2008
A combined inlet consists of a gully grating and an adjacent kerb inlet that has the same length as
the grating (see Figure NA.9 and Figure NA.10). The only benefit of this type of inlet is that it is less
susceptible to blockage than either the gully grating or kerb inlet used separately, as its capacity will
normally be only slightly greater than that of the gully grating.
NA.5.1.4 Linear drainage inlets
Instead of channels and gullies, it is sometimes more convenient to use linear drainage inlets. These can
take a variety of forms some of which incorporate kerbs. The inlet can take the form of a continuous
slot, a series of holes or a continuous grating. Linear drainage inlets can be particularly useful where
the longitudinal gradient of the paved area is low. However, if self-cleansing conditions cannot be
achieved, more frequent maintenance should be carried out to ensure that they operate successfully.
The layout of the linear drainage inlets and the profile of the paved area should be designed to limit
the depth of flow across the paved areas to acceptable limits (see NA.5.2).
The linear drainage inlets should be sized to carry the flow (see NA.5.4 and NA.5.8).
A typical layout for drainage with linear drainage is shown in Figure NA.10.
NA.5.1.5 Drainage from the edge of paved areas
It is not always necessary to have gullies or linear drainage channels. Surface water can often be
effectively drained by direct run-off to the sides of the paved area or by the use of well-maintained
permeable pavements (see NA.4.4.6).
Where edge drainage is used, the layout and profile of the paved area should be designed so that the
depth of flow across the surface is within acceptable limits (see NA.5.2).
Filter strips and filter drains should be designed to the expected flows (see NA.5.9).
NA.5.2 Layout and profile
NA.5.2.1 General
The drainage system should be arranged so as to prevent surface water from flowing across the
entrance, either to or from a public road.
The levels of a paved area should be determined in relation to the levels of:
a)
existing ground;
b) available outfall;
c)
floors and damp-proof courses in adjoining buildings;
d) access points to the paved area;
e)
the top water level of receiving waters;
f)
drainage pathways.
Water draining from a paved area should not be allowed to concentrate along the side of a building
(see Figure NA.10). Where the general ground levels might cause this to happen, a reverse fall should
be applied to a narrow strip around the building so that the water is kept away from the walls.
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BS EN 752:2008
TG
TG
TG
TG
TG
TG
TG
TG
Alternative drainage layout
to parking area for level site
Contours of
original land
Fal
l of
TG
Parking
area
A
TG
lan
d
Outdoor storage area
If there is risk of spillage see 8.5.1
B
A
TG
TG TG
B
TG
TG
TG
Filling station with full retension
light liquid separator (see NA.10)
Public road
Key:
Road with camber section A - A
Arrows indicate direction of fall
of final paved surfaces, exept
where otherwise captioned
TG
Terminal gully
Intermediate gully
Road with cross fall section B - B
Linear drainage inlet
Figure NA.9 — Drainage of typical roads and paved areas by gullies and channels
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BS EN 752:2008
Alternative drainage layout
to parking area for level site
Contours of
original land
Fal
l
Parking
area
of l
and
Outdoor storage area
If there is risk of spillage see 8.5.1
B
A
B
A
Filling station with full retension
light liquid separator (see NA.10)
Public road
Key:
Channel drain section A - A
Arrows indicate direction of fall
of final paved surfaces, exept
where otherwise captioned
Linear drainage inlet
Kerb drain section B - B
Figure NA.10 — Drainage of typical roads and paved areas by linear drainage
If a paved area provides access to workshops, underground garages or storage accommodation that are
at or below the level of the paved area, linear drainage inlets should be used and these should be placed
a minimum of 500 mm away from the building, in order to intercept any water that would otherwise
drain into the building. In addition, to limit the inflow of water, the threshold of the entrance should
be set at a higher level than the general surrounding ground (see NA.5.4).
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BS EN 752:2008
The edge of a paved area may be finished against, and level with, the surrounding natural ground,
provided that the subsoil is suitable and the edge is not subject to heavy loading by traffic or materials.
This method of drainage should not be used where heavy traffic reaches or overruns the edge of a
paved area, or where an adjacent unpaved area could drain a significant amount of flow on to the
paved area.
NA.5.2.2 Limiting depth of flow across paved areas
The maximum distance from the top of catchment to a drainage inlet (such as a valley or kerb line with
gullies, ditch, swale, linear drainage channel or filter strip) is dictated by the shape of the drained area
and by the acceptable depth of flow.
Gradients should be designed to permit quick drainage to collecting channels or gullies. If the gradient
is flat, acceptable tolerances, a slight error in workmanship or minor deformation can result in large
areas of puddles if the area is drained using gullies. Recommended gradients are given in Table NA.7.
Table NA.7 — Recommended gradients for paved areas
Drained area
Gradient
Footpaths
Access roads
Other paved areas
Cross-fall or average camber
1 in 30 maximum
1 in 40 minimum
1 in 40 normal
1 in 60 minimum
Super elevation: road curves not
exceeding 100 m radius
—
1 in 25 maximum
—
Longitudinal gradient or fall
—
1 in 15 maximuma
—
Kerb channels (no channel blocks)
—
1 in 150 minimum
1 in 150 minimum
Kerb channels (with channel blocks or
high-class surfacing)
—
1 in 200 minimum
1 in 200 minimum
a
The first 10 m of an access road from its junction with a major road or public highway should have a
gradient of not more than 1 in 30.
Where the maximum distance of flow to the inlet is greater than 20 m, a check should be made to
ensure that the maximum depth of flow across the paved surface (excepting any channels) is acceptable
having regard to the specific circumstances taking into account the following factors:
— risk of vehicles aquaplaning or splashing bystanders;
— practicality and cost of reducing overland flow distances;
— desirability of short-term retention of water on the surface;
— whether the area is designed to pond (e.g. attenuation in car parks).
There are no published recommendations for the maximum depth of flow but suggested values are
given in Table NA.8. A method of calculating the depth of flow is given in NA.5.2.3.
Table NA.8 — Suggested maximum allowable depth of water during a rainfall
event with a 100 % annual probability (1 year return period)
Situation
Suggested maximum allowable depth of water during a rainfall
event with a 100 % annual probability (1 year return period)
Pedestrian areas (including car parks)
6 mm
Service yards and other hard standing
10 mm
Airports and roads
Consult with relevant authority
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BS EN 752:2008
NA.5.2.3 Calculation method for depth of flow across paved areas
This section is based upon HR Wallingford Report SR606 “Hydraulic Design of Paved Areas” [23]. It is
a simplified method that gives an approximation to flow depth that is considered to be sufficiently
accurate for practical purposes and taking into account the tolerances in laying paving. However, if
more accuracy is required, reference should be made to Report SR606 [23].
The depth of flow may be estimated by using equation NA.6:
D = d × FG × FL × FR × FM
(NA.7)
where:
is the estimated depth of flow, in mm;
d
is the depth of flow for a surface gradient of 1:60, in Location 1, during a rainfall event with
an annual probability of 100 % (1 in 1 year return period) read from Figure NA.11, in mm;
FG
is a gradient factor read from Table NA.9, dimensionless;
FL
is a location factor read from Table NA,10 dimensionless;
FR
is a return period factor read from Table NA,11 dimensionless;
FM
is a surface material factor read from Table NA.12 dimensionless.
Figure 5.7.1
Depth of flow, mm
D
7
6
5
4
3
2
1
0
0
20
40
60
80
100
Length of flow, m
Figure NA.11 — Depth of flow for a surface gradient of 1:60, in Location 1,
during a rainfall event with an annual probability of 100 %
Table NA.9 — Gradient factor, FG
Gradient
1
1:50
FG
0,95
1:60
1,00
2
1:100
1,15
1:1503
1,30
1 The research did not cover gradients steeper than 1:50, so caution should be
exercised in extrapolating the values in this table.
2 Gradients of less than 1:60 are not recommended as puddling is likely unless tight
construction control measures, good quality paving materials and low tolerances
are used.
3 See footnote 2.
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BS EN 752:2008
Table NA.10 — Location Factor, FL
Location
FL
Location 1
1,00
North East, North West (except Cumbria), Midlands, East Anglia,
Southern and South East England, West Country, Wales
Location 2
0,85
Cumbria, Scotland (except northern Scotland) and Northern Ireland
Location 3
0,70
northern Scotland
Table NA.11 — Return Period Factor, FR
Location
(see Table NA.10
for description)
Return period
1 year
2 years
5 years
Location 1
1,00
1,15
1,30
Location 2
1,00
1,15
1,30
Location 3
1,00
1,10
1,25
Table NA.12 — Surface material factor, FM
Surface material
FM
6 mm dense bitumen macadam
1,00
Pavement quality concrete with brush textured
finish up to 1,5 mm
1,25
Pavement quality concrete with brush textured
finish up to 4 mm
1,40
Hot rolled asphalt with 20 mm chippings
1,40
NOTE
Factors may be interpolated for other materials.
Research indicates that for typical paving materials and rainfall conditions the ponding normally lasts
for up to 10 minutes before it subsides to below 75 % of the maximum depth. HR Wallingford Report
SR606 [23] provides more information on the duration of rainfall that produces the maximum ponding
and the duration of ponding.
NA.5.3 Simple design method for areas drained by gullies
In simple cases, where ponding on the surface can be tolerated during heavy rainfall, the system of
drainage inlets will be adequate if the maximum area draining to any gully is no more than 180 m2 and
if a double gully is provided at low points on a profile. Where the surface is to be adopted by a highway
authority this is subject to approval by the adopting authority. This method is applicable:
— for the design of drainage on estate roads having a width of 10 m or less (including the width of
any footways included) and a longitudinal gradient steeper than 1 in 100; or
— for the design of drainage on other types of paved areas where the maximum length of flow to
each gully is less than 40 m,
— where the area of the waterway of the gully is > 0,09 m2.
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BS EN 752:2008
NA.5.4 Calculation of flow rates
The general layout of the drainage system should first be decided and the total paved area then split
into suitable sub-areas taking into account the factors detailed in NA.5.2 and NA.4. The design flow
from each sub-area is the peak flow rate calculated using equation (E.7) in annex E.
Where the run-off from adjacent paved or pervious areas or buildings will discharge onto the paved
area these flows should also be included in the calculations.
NA.5.5 Detailed method for hydraulic design of gullies without channels
NA.5.5.1 Introduction
The detailed method for hydraulic design of areas drained direct to terminal gullies involves the
following steps:
a)
calculate flow to each gully (see NA.5.4);
b) check that the terminal gullies have adequate capacity (see NA.5.5.2).
NA.5.5.2 Hydraulic capacity of terminal gullies
Where gullies are located at the downstream ends of collecting channels and at low points in the
paved area, they are termed terminal gullies. Terminal gullies should be generously sized, as any lack of
capacity is more likely to cause flooding than is the case with intermediate gullies. Alternatively, double
gullies may be used.
The capacity of terminal gullies is best determined experimentally. However, where experimental data
are not available, their capacity can be estimated using equations (NA.7) and (NA.8) as follows.
If the flow is weir-type:
Qi =
Lw h1,5
24000
(NA.8)
If the flow is orifice-type:
Qi =
Ai h0,5
12000
(NA.9)
where
Qi
is the total flow entering the gully, in litres per second;
Lw
is the total length of the openings, measured around the perimeter of the grating, in millimetres;
Ai
is the total area of openings that are submerged by the flow, in square millimetres;
h
is the depth of water above the mean level of the openings, in millimetres.
Alternative values of the water level at the outlet should be calculated; the higher of the two levels is
the actual level that will occur.
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BS EN 752:2008
NA.5.6 Detailed method for hydraulic design for areas drained by gullies and channels with
longitudinal gradients steeper than 1 in 300
NA.5.6.1 Introduction
The detailed method for hydraulic design of areas drained by gullies where the longitudinal (or flattest)
gradient of the paved surface is steeper than 1 in 300 (0,33 %) involves the following steps:
a)
calculate flow in channel (see NA.5.4);
b) calculate depth of flow in channel (see NA.5.6.2);
c)
calculate the capacity of terminal gullies (see NA.5.5.2);
d) calculate the spacing of any intermediate gullies to keep the depth and width of flow in the
channel to acceptable levels and to limit the flow to terminal gullies to with capacity (see NA.5.6.3).
Further information is given in HR Wallingford Report SR533 [22] and Design Manual for Roads and
Bridges Volume 4 Section 2 [24].
NA.5.6.2 Collecting channels
Collecting channels are usually of shallow triangular cross-section and have the same longitudinal
slopes and cross-falls as the paved surfaces that they drain (see Figure NA.12). Channels with other
cross-sectional shapes may, however, be used. The discharge capacity of a particular channel is
normally limited by the maximum depth or width of flow that is acceptable taking account of the use
of the surface (e.g. pedestrian area, storage area, road). For roads, account should be taken of the
type of road, the speed limit, lighting, proximity of footway or cycleway and the width of any hard
strip or hard shoulder. Where the road is to be adopted, reference should be made to the highway
authority (NA.13.8).
Where pedestrians need to cross collecting channels, the width of flow calculated using the design
rainfall (see NA.4.2, Table NA.1), should not exceed 500 mm.
The Manning equation (equation, E.2) can be used to calculate the capacity of a collecting channel. For
convenience, it can be rewritten as:
Q = 1 000 ×
KA1,67 JE 0,5
P1,33
(NA.10)
where
Q
is the channel discharge, in litres per second;
K
is the Manning coefficient of the channel, in metres raised to the power one third, per second
(see Table NA.8);
A
is the cross-sectional area of the flow, in square metres;
JE
is the longitudinal slope of the channel, expressed as a decimal fraction;
P
is the wetted perimeter, in metres.
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BS EN 752:2008
For channels of shallow triangular cross-section, equation (NA.6) may be approximated by:
Q = 3,0 × 10−6 Cy 2,67
(NA.11)
where
Q
is the channel discharge, in litres per second;
y
is the depth of flow, in millimetres (see Figure NA.8);
C
is the channel criterion (dimensionless), calculated from equation (NA.12):
C = Kb JE 0,5
(NA.12)
where
K
is the Manning coefficient of the channel, in metres raised to the power one third, per second
(see Table NA.13);
b
is the cross-fall of the channel (ratio of channel depth to top width) (see Figure NA.12);
JE
is the longitudinal slope of the channel, expressed as a decimal fraction.
NOTE
The vertical scale has been exaggerated for illustration purposes.
Figure NA.12 — Channel cross-sections
Table NA.13 — Manning coefficients for channels
Type of channel
Manning coefficient, K
m1/3/s
Smooth concrete
90
Concrete with grit
70
Smooth bituminous paving
70
Bituminous paving with grit
55
NA.5.6.3 Terminal gullies
Terminal gullies should be positioned at the ends of channels and at low points. These should be
designed in accordance with NA.5.5.
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BS EN 752:2008
NA.5.6.4 Spacing of intermediate gullies
Intermediate gullies are generally used where:
•
there would otherwise be too great a depth of ponding at the downstream end of a collecting
channel;
•
the depth or width of flow in the collecting channel would otherwise exceed chosen limits.
Kerb inlets, or gratings set in the base of the collecting channel, may be used as intermediate gullies.
Kerb inlets generally have a lower capacity than gully gratings of the same length, but are less liable to
damage by vehicles. Kerb inlets can be set back from the kerb as shown in Figure NA.13, in which case
they have a higher capacity and act in the same way hydraulically as terminal gullies (see NA.5.5). At
points where the direction of cross-fall changes, gully gratings are preferable to kerb inlets because of
their greater hydraulic efficiency.
The percentage of flow intercepted by a gully depends upon:
•
the properties of the channel in which the gully is installed;
•
the design of the gully.
At low flows, a gully collects all the flow, but, as the flow towards the gully increases, the percentage
collected decreases, although the actual flow intercepted by the gully increases.
The following factors should be considered in specifying the spacing of intermediate gullies:
a)
limits on the maximum width and depth of flow in the collecting channel;
b) limits on the amount of flow bypassing each gully;
c)
likelihood of blockage of the gully and/or its grating;
d) the frequency of cleaning.
The spacing of intermediate gullies that is necessary to prevent the depth or width of flow in the
collecting channel from exceeding chosen limits can be determined by checking whether the calculated
amount of flow bypassing a gully is acceptable.
The capacity of a gully can be increased if some flow is allowed to bypass the gully and continue to a
gully further downstream. The increase in capacity can be significant in the case of kerb inlets, which
have a relatively low efficiency in steep channels. The total proportion of flow bypassing a gully (i.e.
the sum of the carry-over flow and the carry-past flow: see Figure NA.7 and Figure NA.8) should not
normally exceed one-fifth of the flow approaching the gully. A reduction of the spacing decreases the
amount bypassing and the maximum width and depth of flow. An increase of the spacing will have the
opposite effect.
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BS EN 752:2008
Figure NA.13 — Alternative arrangements of gullies
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144
BS EN 752:2008
Figure NA.14 — Flow to a rectangular gully grating
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145
BS EN 752:2008
The flow into an intermediate gully should be calculated using the method described below. Further
information is given in HR Wallingford Report SR533 [22] and Design Manual for Roads and Bridges
Volume 4 Section 2 [24].
The capacity Qg of the gully inlet should be calculated from:
Qg = ηmQu
(NA.13)
where:
η
is the gully efficiency which is calculated from equations (NA.10) or (NA.12) as appropriate;
m
is the maintenance factor taken from Table NA.14, dimensionless;
Qu
is the upstream flow in the channel, in litres per second.
Table NA.14 — Typical values of maintenance factor m
Situation
Maintenance factor m
Well-maintained urban roads
1,0
Paved areas subject to less frequent maintenance
0,9
Paved areas subject to substantial leaf falls or vehicle spillages
0,8
Sag points on gradients
0,7
The gully efficiency (%) of a gully grating can be calculated from:
( H)
η = 100 − Gd Qu
(NA.14)
where:
Gd
is the design grating parameter in seconds per square metre;
H
is the depth of flow in the channel at the kerb
The design grating parameter Gd should be taken from Table NA.15 depending on the calculated
grating parameter from equation (NA.11).
Table NA.15 — Design grating parameter Gd
Design grating parameter
Gd [s/m2]
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146
Applicable range of grating
parameters calculated from
equation (NA.11)
30
≤ 30
45
30,1–45
60
45,1–60
80
60,1–80
110
80,1–110
BS EN 752:2008
The gully parameter is calculated from:
G=
69Cb
(NA.15)
Ag0,75 p
where:
Ag
is the area, in square metres, of the smallest rectangle parallel to the kerb that includes all
the slots;
p
is the waterway area as a percentage of the grating area Ap ;
Cb
is a coefficient relating to the bar pattern and should be taken as 1,75 for transverse bars
and 1,5 for other bar alignments (e.g. longitudinal, diagonal or curved bars).
The gully efficiency (%) for a kerb inlet can be calculated from:
η = 100 −
36,1Qu
(NA.16)
Li H1,5
where:
H
is the depth of flow in the channel at the kerb;
Li
is the length of the opening in the line of the kerb.
If the gully efficiency is less than 50 %, the design should be reviewed to improve the efficiency.
NA.5.7 Detailed method for hydraulic design for areas drained by gullies and channels with
longitudinal gradients flatter than 1 in 300
The method described below is based on TRRL Laboratory Report 602 [25].
It should be noted that results obtained using this method will not be consistent with results from the
method described in NA.5.4.
For a drainage channel of constant depth and trapezoidal cross-section, and assuming some grit in the
channel, the outlet spacing is given by:
J=
3,74 × 10−4 ( S + 0,5Kw ho )
(iW )
0,923
ho 1,231
0,769
(NA.17)
where:
J
is the outlet spacing, in metres;
S
is the width of the bottom of the trapezoidal channel, in millimetres;
Kw
is the sum of the cotangents of the angles of inclination of the channel sides from the horizontal
(dimensionless);
ho
is the channel depth, in millimetres;
i
is the rainfall intensity, in litres per second per square metre;
W
is the width of road, in metres.
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For a drainage channel with a triangular cross-section, with one face vertical, as alongside a road edge,
and assuming some grit in the channel, the outlet spacing is given by:
J = 1,02Cr
1,75 w 
 3  0,75 
JE 

 1+ Kc B
 iW 
 1293iW 0,875 




1,4375  B
(NA.18)
where:
J
is the outlet spacing, in metres;
Cr
is the cross-fall, expressed as a percentage;
B
is the maximum flow width, in metres;
Kc
is a coefficient dependent upon cross-fall, from Table NA.16;
JE
is the longitudinal gradient, expressed as a percentage;
w
is an index, from Table NA.16;
i
is the rainfall intensity, in litres per second per square metre;
W
is the width of road, in metres.
Table NA.16 — Values of Kc and w
Cross-fall, Cr
%
Index, w
Coefficient, Kc
0,5
117
2,260
1,0
190
2,190
1,5
265
2,125
2,0
326
2,060
2,5
380
1,995
3,0
416
1,930
4,0
448
1,800
5,0
448
1,670
w = 2,32 – 0,13Cr
NA.5.8 Hydraulic design for areas drained by linear drainage channels
This section is based upon HR Wallingford Report SR581 “Hydraulic Capacity of Drainage Channels with
Lateral Inflow” [26].
The hydraulic capacity of a constant depth channel may be calculated using:

L 
Q = 2,66 A1,25  6,74S 0,7 + 0,4 + b
h 

where:
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Q
is the hydraulic capacity, in cubic metres per second;
A
is the channel cross-sectional area, in square metres;
(NA.19)
BS EN 752:2008
S
is the channel slope, dimensionless;
L
is the channel length, in metres;
h
is the design water depth, in metres
with
b
0,1325 – 0,00022 for S <= 1/200
b
0,00044 for 1/200 < S <= 1/30
For channels with a varying depth, the hydraulic capacity can be calculated using equation (NA.11),
with h as the depth of the most upstream channel unit and S being the average gradient of the invert.
NA.5.9 Filter strips and filter drains
Filter strips are vegetated surfaces that allow water to drain evenly along the entire length of the edge
of an impermeable area. The vegetation both slows the rate of flow and filters the flow, removing
some of the pollutants through filtration and sedimentation. They can be integrated with filter drains
or swales.
Filter drains are trenches filled with permeable filling material that drain water evenly from the edge
of an impermeable surface over its entire length. A porous pipe, part way up the trench can be used to
take flows that do not infiltrate into the ground to a surface receiving water. The flow is attenuated by
the storage in the permeable fill.
The paved areas should be designed so that the surface water discharges as evenly as possible over the
length of the edge of the paved surface.
NA.6 Sewers with steep gradients (8.4.2 and 9.4.6)
Research has demonstrated that high velocities of flow in drains and sewers laid at steep gradients do
not cause increased erosion of pipes [27] or deposition of solids [28] for commonly used sewer materials.
Experience has shown that drains may therefore be laid at gradients to optimize excavation and cost.
Care should be taken with the design and construction of manholes so that excessive turbulence is not
caused, which can lead to fouling. Where necessary, this can be mitigated by replacing the channel with
an access pipe.
Where sewers with steep gradients are required, consideration should be given to consequences of
high velocities such as:
— air entrainment and its effects;
— release of hydrogen sulfide;
— erosion;
— the need for energy dissipation measures on super-critical flow to sub-critical flow;
— the need for thrust restraint;
— the need for special safety measures for operatives.
Backdrop manholes, ramp manholes or vortex manholes may be installed in a sewer system to dissipate
excessive static head in a controlled manner, thereby avoiding the installation of sewers with steep
gradients and meeting any imposed velocity limitation.
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Where large grit volumes are included in high energy flows and there are either sharp changes in
direction or significant steps in the pipe invert, erosion of pipe material or coating can occur unless
resistant materials are used. In particular, the bottom bend of a backdrop manhole can be vulnerable.
NA.7 Combined sewer overflows (8.5.5)
Over and above any requirements arising from compliance with the standards described in NA.8.2,
there is a general requirement for all new or unsatisfactory sewer systems to be designed to carry flows
without spilling until the incoming flow exceeds that calculated by Formula A [30], which is based on
the dry weather flow, population and trade effluent flow of the upstream catchment.
DWF + 1360P + 2E litres/day
(NA.20)
where:
DWF = dry weather flow;
P = population served;
E = trade effluent flow.
The constants used in the formula should be adjusted for particular types of trade effluent, for small
receiving waters or for sewer systems with large storage capacity.
The water pollution control authority (see NA.13.4) can also impose further discharge requirements
(see NA.8).
Further advice on the design of combined sewer overflow structures can be found in Guide to the Design
of Combined Sewer Overflow Structures [31] and the WaPUG Guide to the Design of CSO chambers to
incorporate screens [32].
NA.8 Environmental considerations (8.5 and 9.5)
NA.8.1 Introduction
Where receiving waters are affected, the relevant authority should be consulted at an early stage.
The major UK source documents are the Urban Pollution Management (UPM) Manual [33], which is a
planning guide for the management of urban wastewater discharges under wet weather conditions
and the Urban Wastewater Treatment (UWWT) Regulations guidance [34], [35], [36], which set out
the regulatory policy of the Environment Agency for England and Wales in respect of sewer system
discharges and their future consent standards. Reference should be made to these documents for more
detailed information.
NA.8.2 Control of pollution
NA.8.2.1 General
All legitimate uses recognized for surface waters can be affected to some extent by wet weather
discharges from sewer systems. However, river aquatic life, bathing and general amenity have been
specifically identified in the UWWT Regulations Guidance [34], [35], [36] for England and Wales and
appropriate Environmental Quality Standards have been developed.
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The UK policy for the protection of the aquatic environment is based on Environmental Quality
Objectives (EQOs) that specify the desired uses of a water body. Environmental Quality Standards (EQSs)
are then defined such that, when achieved, the EQOs are met and the desired uses are protected.
NA.8.2.2 Standards for protecting river aquatic life
Over the years, Environmental Quality Standards and procedures of varying complexity have been
developed for protecting river aquatic life. The simpler procedures make a number of conservative
assumptions about the nature of the receiving water, and therefore, include large built-in safety factors.
The complex procedures require detailed modelling and are likely to produce more cost effective
designs, however this level of detail is not always feasible or justified in many cases.
Environmental Quality Standards have been developed to ensure protection of river aquatic life during
short term pollution events. These intermittent standards are expressed in terms of maximum allowable
frequencies for specified threshold concentrations and durations of dissolved oxygen (DO) and un-ionized
ammonia and are presented in the UPM Manual [33]. They assume that the wet weather discharges do
not contain unusually high levels of other substances, which can be damaging to aquatic life.
The application of these fundamental standards require the modelling of the environmental impact of
the discharge on the receiving water. This may involve use of a complex dynamic river flow and quality
model or something simpler. Modelling of the sewer system (flow and sewage quality) and, where
relevant, the sewage treatment works is also usually necessary. This modelling may involve detailed
dynamic models or may use simple techniques.
NA.8.2.3 Standards for protecting bathing and shellfish waters
Two approaches are used in the UK:
a)
Site-specific EQSs
The UWWT Regulations Guidance [34], [35], [36] set out EQSs for use in England and Wales for coliform
bacteria in waters which have been identified under the provisions of the Bathing Water Directive [37]
and the Shellfish Waters Directive [38]. These standards are defined in terms of bacterial concentration
thresholds and exceedance periods and are designed to ensure compliance with the Bathing Water
Directive [37] or the Shellfish Waters Directive [38]. The exceedance period for bathing waters is the
average period over a number of bathing seasons (a bathing season is generally May to September). To
use the bacterial EQSs directly for planning purposes it is necessary to be able to model the transport
and fate of bacteria following a discharge. A revised Bathing Waters Directive [39] has now been
approved and is due to come into force in 2008; this is likely to affect the guidance.
b) Uniform emission standards
The UWWT Regulations Guidance [34], [35], [36] also set uniform emission standards (see 8.5.2) for
England and Wales, which can be used without the need for environmental modelling studies. The
standards in the guidance limit the average number of discharges from CSOs to identified bathing
waters or shellfish waters, or in close proximity to such waters, as a result of independent rainfall
events to a specified spill frequency. The spill frequency standards have universal application and are
easily applied and understood, but necessarily have large built-in safety factors. A revised bathing
waters directive [39] has now been approved and is due to come into force in 2008; this is likely to
affect the guidance.
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NA.8.2.4 Standards for protecting amenity use
The UWWT Regulations Guidance [34], [35], [36] set out uniform emission standards for England and
Wales in terms of solids separation requirements for CSO discharges to protect amenity use from
aesthetic pollution. There are three levels of standard based on different amenity use categories and
spill frequencies. There is no requirement to modify or upgrade existing satisfactory CSOs to meet these
emission standards. In using the emission standards, it is essential that all areas that could reasonably
be affected by the discharge are considered and the highest amenity category applied.
NA.8.3 Drains and sewers near water abstraction areas
Installation of drains and sewers can be restricted in areas where water is to be abstracted for human
consumption. If in such areas drain and sewer systems are unavoidable, the designer should take
measures to ensure permanent control and to prevent pollution of the ground and/or groundwater.
Such measures can include:
— installation of an additional equally watertight surrounding pipe;
— installation of alarm systems for leakage and breakage;
— installation of house connections directly to manholes and not to the sewer;
— special requirements for system components and method of construction.
NA.9 Materials selection (8.6.4 and 9.5.3)
NA.9.1 General
The materials for pipes, pipe joints, bedding, manholes and their associated fittings, associated building
works and the type of cement and mix to be employed should be selected to ensure satisfactory service
for the life of the drain or sewer system. Materials should be specified in accordance with the relevant
European Standard or British Standard. A list of relevant standards for materials commonly used in the
UK is given in table NA.17. Factors to be taken into account in selecting materials should include:
— the nature of the effluent and the possibility of chemical attack or mechanical damage (including
damage resulting from cleansing or rodents);
— the nature of the ground conditions and the possibility of subsidence or chemical attack;
— the physical and chemical characteristics of the materials themselves;
— the quality of workmanship that can be expected and the degree of supervision to be provided.
Further information on the selection of pipes can be found in the relevant product standards and in the
“Materials selection manual for sewers pumping mains and manholes” [40].
NA.9.2 Resistance to chemical attack
NA.9.2.1 General
Pipes and joints in materials referred to below are generally suitable for use in sewers and drains
conveying surface water, foul sewage and trade effluent that can legally be discharged to public
sewers. The ground conditions in which the sewer is to be laid can be corrosive to certain pipe and/or
jointing materials and this can affect the choice of materials. Where a drain or sewer is liable to carry
untreated and corrosive trade effluents, further consideration should be given to possible protective
measures. Liquids at elevated temperatures are likely to be significantly more aggressive than those at
ambient UK temperatures.
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Materials can suffer attack from:
— discharge of effluent from industrial processes (e.g. electroplating works);
— discharge of effluent from chemical laboratories;
— discharge of sewage, where due to long retention periods septicity occurs;
— aggressive groundwaters (e.g. in contaminated ground);
— less aggressive groundwaters, where there is a convenient drainage path that allows groundwaters
to be continually replenished.
Table NA.17 — Materials and products commonly used in sewerage construction in the UK
Relevant standards
BS EN 206-1
Material or product
Concrete
Notes
Specification, performance
production and conformity
BS 8500
Complementary standard to
BS EN 206
BS 8110
Specifies structural use of concrete
BS EN 197
Cement
BS EN 12620
Aggregates for concrete
BS 8500-2 specifies requirements for
recycled aggregates
BS EN 13242, PD 6682-6:2003,
BS EN 13055-2
Bedding materials for pipes
WIS 4-08-02 [41] and the
Specification for Highway Works [42]
give guidance on selection of pipe
bedding materials
BS EN 295, BS 65
Clay pipes, fittings and joints,
perforated pipes manholes jacking
pipes gullies and extra chemically
resistant pipes
BS EN 1916, BS EN 1917, BS 5911
Precast concrete pipes, inspection
chambers, manholes and gullies
BS 437, BS EN 877, BS 416
Grey iron pipes and gullies
BS EN 598
Ductile iron sewer pipes and fittings
BS EN 1852
PP pipes
BS EN 12666
PE pipes
BS EN 14364
GRP (UP) pipes
BS EN 14758
Mineral modified PP pipes
BS EN 13476
Thermoplastics structured wall pipes
BS 4660
Ancillary underground drainage
thermoplastics products
BS 7158
Manholes and inspection chambers
(plastic)
BS EN 124
Manhole covers and frames and gully
gratings for roads
BS EN 1433
Linear drainage channels
BS 7099
BS 7097 is the complementary
standard to BS EN 124
BS EN 13101
Manhole steps
BS EN 14396
Manhole ladders
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NA.9.2.2 Concrete and materials containing cement
Normal domestic sewage is not aggressive to Portland cement concrete or cement composite. However,
sewage, which becomes devoid of oxygen will produce hydrogen sulfide that, in turn, can produce
sulfuric acid that is aggressive to cement products. The majority of ground waters are similarly not
aggressive to such materials (see concrete in aggressive ground [43] and BS 8500).
The cement content, the water/cement ratio and the compaction will have considerable effect on the
resistance of concrete to chemical attack. These factors should, therefore, be considered when specifying
concrete in cases of potential chemical attack (see Concrete in aggressive ground [43] and BS 8500). In
those cases, where it is shown that concrete can be attacked, specialist advice should be obtained.
Concrete pipes and fittings complying with BS EN 1916, BS EN 1917 and BS 5911 are normally resistant
to attack by sulfates in solution and acids of pH 5 and above.
NA.9.2.3 Protection of ductile iron
BS EN 598 defines the standard protection for ductile iron drain and sewer pipes. Generally, the pipes
are externally coated with zinc (or zinc/aluminium) with an epoxy topcoat. Where external conditions
are particularly aggressive, additional external protection should be considered (e.g. polyethylene
sleeving complying with BS 6076 for zinc-coated pipes; or in extreme circumstances, tape wrap for
zinc-coated or zinc/aluminium-coated pipes). Generally, the pipes are internally lined with calcium
aluminate cement mortar. Various alternative internal coatings are available giving different levels of
protection, the manufacturers advice should be sought regarding these special pipe linings.
NA.9.2.4 Protection for grey iron pipes
BS 437; BS 416 and BS EN 877 define the standard coatings for cast iron drain pipes. Generally, above
ground pipes are coated externally with a synthetic paint, whilst below ground pipes have an additional
layer of zinc under the synthetic paint. Internally, pipes are coated with a two-pack epoxy paint. Where
conditions are particularly aggressive, additional protection should be considered (e.g. polyethylene
sleeving complying with BS 6076 or in extreme circumstances, tape wrap, for below ground pipes;
additional coats of epoxy paint for above ground pipes).
NA.10 Separators (8.7.2 and 9.6.2)
NA.10.1 Introduction
Where separators are provided, provision should be made for them to be emptied, cleaned and maintained.
NA.10.2 Grease separators
Guidance supporting Building Regulations in England and Wales [3] and Scotland [5] recommend the
provision of grease separators or other effective means of grease control on drainage from commercial
hot food premises.
Grease separators should be sited so that emptying can be carried out without contaminating food
preparation or food storage areas.
NA.10.3 Light liquid separators
Detailed guidance from the relevant authority on the provision of light liquid separators can be found
in “Use of oil separators in surface water drainage systems” Pollution prevention guideline no. 3 [44].
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NA.11 Design for self cleansing (8.7.3 and 9.6.3)
NA.11.1 Sediment transport
Information on the design of drains and sewers to avoid excessive sedimentation can be obtained
from the Building Regulations [3], [4], [5], [6], for building drainage, and Sewers for Adoption [1] or
Sewers for Scotland [2], for public sewer systems. The design of drains and sewers to control sediment
problems is considered in more detail in CIRIA Report 141 [28].
With the exception of small diameter foul drains and sewers, the guidance on minimum velocities and
gradients is based on average sediment conditions and assumes that some sediment deposition in the
pipes can be tolerated (up to 2 % of the diameter). Higher velocities and steeper gradients should be
used where high sediment loads are expected where, for example:
— a drain or sewer system is likely to receive excessive (i.e. more than the carrying capacity of the flow)
amounts of sediment (e.g. sand, etc.) and/or debris;
— windblown sand is present, e.g. in coastal areas;
— there are poorly maintained roads or road gullies – poorly maintained road surfaces can lead to grit
or sediment from surfacing materials being washed into the drain or sewer system;
— industrial premises that discharge significant amounts of sediment into the drain – catch pits will
normally be required to prevent excessive amounts of sediments entering public sewer systems or
receiving waters.
NA.11.2 Minimization of blockages
NA.11.2.1 General
NA.11.2.2 Minimum pipe sizes
Foul drains and sewers carrying wastewater from conventional WCs should be a minimum of DN 100.
Where no WCs are connected or are likely to be connected, a minimum of DN 75 may be used although
because of the availability of pipes and fitting DN 100 is usually used.
Sewerage Undertakers do not usually adopt lateral drains or sewers with a nominal diameter less than
those shown in Table NA.18.
Table NA.18 — Minimum diameters for adoptable gravity foul drains and sewers
Type of drain or sewer
Number of properties
DN 100
Lateral drain
Sewer
Sewer
Minimum diameter
10 properties or less
More than 10 properties
DN 100
DN 150
NA.11.2.3 Minimum gradients for small diameter drains and sewers
Foul drains and sewers should be laid as steep as practicable. Where hydraulic design is carried out
using probability methods (see 8.4, 9.4, 9.6.3, Annex E), drains and sewers are usually considered to be
self-cleansing if they are laid not flatter than the gradients given in Table NA.19.
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Table NA.19 — Minimum recommended gradients for foul drains
Peak flow
[l/s] (1)
Pipe size
[mm]
Minimum
gradient (2)(3)(4)
<1
75
100
1 in 40
1 in 40
>1
75
100
150
1 in 80
1 in 80 (5)
1 in 150 (6)(7)
1)
Peak flows should be based on probability flow calculation methods.
2)
These gradients have been empirically demonstrated on the basis of 6 l WC flush volumes. Further research
is necessary to evaluate the recommended gradients for use in system with very low WC flush volumes.
3)
Exceptionally, where the length of drain or sewer serving a small number of properties is very long, steeper
gradients can be required.
4)
Where ground settlement is expected, steeper gradients are recommended.
5)
Minimum of one WC connected.
6)
Minimum of five WCs connected.
7)
Exceptionally, where a 150 mm diameter pipe is used to carry flows from less than five WCs, the minimum
gradient should be 1 in 60.
NA.11.2.3.1 Minimum velocities for larger diameter foul drains and sewers
For the design of foul drains and sewers up to DN 300, where design flows are based on population (see
clauses 8.4, 9.4, 9.6.3 and Annex E), the minimum velocity criteria specified in 9.6.3 (0,7 m/s) is generally
used. A flow of two times the average daily domestic flow (see Annex E, Table E.4) is assumed to occur
at least once daily and is used for this calculation. For larger sewers, higher minimum velocities should
be used; further information is available in a report by CIRIA [28].
In small diameter drains and sewers (DN 150 or less), where these velocities cannot be achieved, the
method given in NA.11.2.2 should be used.
NA.11.3 Combined and surface water drains and sewers
NA.11.3.1 Minimum pipe sizes
Surface water drains and sewers should be a minimum of DN 75. Combined drains and sewers should
have the same minimum size as foul drains (see NA.11.2.2).
Sewerage Undertakers will not normally adopt combined or surface water sewers less than DN 150.
NA.11.3.2 Minimum gradients in smaller diameter combined and surface water drains and sewers
DN 75 and DN 100 surface water drains and sewers should be laid no flatter than 1 in 100. For larger
sizes, see NA.3.
Combined drains and sewers should be designed to comply with the relevant recommendations for
both foul and surface water drains and sewers.
NA.11.3.3 Minimum self-cleansing velocities for larger diameter combined and surface water drains
and sewers
Surface water drains and sewers DN 150 to DN 900 should be designed to achieve a self-cleansing
velocity of 1,0 m/s in pipe full conditions.
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Combined drains and sewers should be designed to comply with relevant recommendations for both
foul and surface water sewers.
For larger sewers, higher minimum velocities should be used; further information is available in CIRIA
Report 141 [28].
NA.11.4 Inverted siphons
Higher velocities will generally be required to control sedimentation in inverted siphons, particularly
where the rising part of the pipeline is steep.
In order to achieve self-cleansing velocities in inverted siphons, it is generally necessary to construct two
or more parallel pipelines. The first pipeline is designed to achieve self-cleansing velocities at least once
a day in dry weather flow conditions (see NA.11.2.3.1). When the flow exceeds this, the water level will
rise and flows will spill into a second parallel pipeline. In combined sewers, additional pipelines should
be constructed to ensure self-cleansing conditions in wet weather flows.
Inverted siphons should incorporate access for draining the sewage and removing sediments from the
lowest point of the siphon.
NA.12 Access to drains and sewers (8.7.4 and 9.6.4)
NA.12.1 General
Access is required to drain and sewer systems for inspection, maintenance and removal of debris. This
can be provided through the following types of access point:
a)
observation fittings are only intended to view the level of the effluent in order to establish the
location of a problem;
b) rodding points are small-diameter non-man access connections at the upstream end of a drain or
sewer to facilitate introduction of equipment for cleaning or inspection, downstream of the access
point. This can include a gully incorporating a rodding point;
c)
inspection chambers are non-man entry chambers used to facilitate introduction of equipment for
cleaning and inspection;
d) manholes are chambers used for entry of personnel and equipment.
Where access for entry by personnel is provided, means of access should allow for both safe access to,
and egress from, the drain and sewer system. Additionally, adequate safe working space should be
provided within the system. Further information can be found in Safe Working in Confined Spaces [29].
Where it is anticipated that personnel will enter a pipe for any reason, the size of the pipe should be
at least 900 mm high to allow safe access and egress.
NA.12.2 Provision and spacing of access
NA.12.2.1 Provision of access to drains and sewers without entry by personnel
Access should be built on drains and sewers at every:
a)
head of branch;
b) change of alignment or gradient;
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c)
junction of two or more sewers;
d) change in size.
Personnel access should be provided where individual drainage fittings, such as intercepting traps, antiflooding devices, CSO screens, weirs, siphons, penstocks or backdrops require regular maintenance and
where the maintenance could not be carried out from the surface.
Table NA.20 indicates the recommended maximum distances between rodding points, access fittings,
inspection chambers and manholes. These are based on manual cleaning techniques and the need for
removing debris. Where only remotely operated and automatic equipment will be used for maintenance
(e.g. jetting), the spacing may be increased.
Where a branch joins a main pipe without an inspection chamber or manhole at the junction, access
should be provided on the branch within 12 m of the junction.
Where maintenance is intended to be carried out using only remotely operated equipment, a deep
inspection chamber that permits use of over-pumping equipment, suction hose (vacuum tanker), and
CCTV inspection equipment may be used instead of a manhole on sewers no greater than 225 mm,
and in such cases the spacing for a manhole in Table NA.20 will apply. Deep inspection chambers can
restrict the use of trenchless technology equipment and should not be used in areas where excavation
for repairs would be unacceptable.
Table NA.20 – Recommended maximum spacing of access provision (in metres)
Distance from
To branch or
junction
To inspection
chamber (type 1)
To inspection
chamber (type 2)
To manhole
Start of external drain*
12
12
22
45
Rodding point
22
22
45
45
Inspection chamber (type 1)
12
–
22
22
Inspection chamber (type 2)
22
22
45
90
Manhole
–
–
45
100 (up to 200 for
drains and sewers
intended for entry
by personnel – see
NA.12.2.2)
* Stack or ground floor appliance without a rodding point
NOTE for type 1 and 2 see clause NA.12.5.2
NA.12.2.2 Provision of access to drains and sewers for entry by personnel
Manholes at each change of alignment are not always necessary; however, in these cases, special
measures need to be taken to allow the position of the drain or sewer to be located accurately. Manholes
should be placed at every significant change in gradient or size, and at major junctions.
The recommended maximum access spacing is 200 m for drains and sewers, not exceeding DN 1800.
Due consideration should always be given to remote inspection, ventilation and the safety of personnel
working in the drain or sewer and the distance which silt, repair materials and casualties can be conveyed.
NA.12.3 Dimensions of observation fittings
Observation fittings are not intended for connections or maintenance they are only intended to view
the level of the effluent in order to establish the location of a problem.
The horizontal cross-sectional dimension of the opening should not be less than 100 mm and not be
more than 300 mm.
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NA.12.4 Dimensions of rodding points
Rodding points should be not less than DN 100 and preferably the same diameter as the drain or sewer.
They should be no steeper than 45° from the horizontal.
NA.12.5 Layout and dimensions of inspection chambers
NA.12.5.1 General
Inspection chambers are intended for inspection and maintenance activities, but not for entry by
personnel. They should permit the introduction of equipment for the following activities into any of
the incoming or outgoing pipes:
a)
inspection of the drain or sewer by CCTV;
b) clearance of blockages by rodding or jetting;
c)
sealing the end of the incoming or outgoing pipe and undertaking a leak-tightness test using
either the water or air pressure test method.
In some cases the size of the equipment required will depend on the diameter of the pipe. For example
a CCTV camera unit needs to be mounted so that the centre of the camera moves along the axis of the
pipe. The camera unit for use in a large pipe could therefore be larger than one designed for use in a
small pipe. Dimensions will therefore depend on the size of the main pipe and the number, size and
position of branches.
The main channel should extend the whole length of the chamber. Channels should comprise a
half-round section plus vertical benching from the top edge of the half-round section to a height of
not less than that of the soffit of the outlet where it should be rounded off to a radius of about 25 mm
and sloped upwards to meet the wall of the chamber. Where the connecting angle is greater than 45°,
three-quarter section bends should be used. Vertical and side benching should be shaped so as to
contain the flow without permitting fouling and to facilitate the cleaning of branches.
In inspection chambers, the benching slope should be about 1:12.
NA.12.5.2 Layout
Inspection chambers can be in one of two forms.
a)
Type 1: an access fitting comprises an opening in the crown of the pipe, which is widened into a
small chamber capable of being fitted with a cover. The opening can have the same plan length
(parallel to the axis of the pipe) and width or it can be longer than the width. Benching is not
necessary as the width of the chamber is not significantly larger than that of the drain or sewer.
Access fittings can be installed with the cover at surface level for direct access or installed within a
chamber to provide a sealed drainage system. They often incorporate junctions or bends.
b) Type 2: a chamber that is wider than the diameter of the pipe which therefore incorporates a
separate channel and benching.
Both forms allow access into the pipe for inspection, testing and cleaning in both directions.
Two classes of inspection chamber are defined depending on dimensions with type 2 inspection
chambers being larger than type 1 inspection chambers.
Where pipes connect at an inspection chamber, the flows should combine in preformed swept channels.
The horizontal angle between any incoming pipe and the outgoing pipe should not be less than 90°.
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Bends with an angle of not more than 45° may be used immediately outside inspection chambers on
the inlet, the outlet or both pipes. Bends may also be accommodated using a curved open channel
within the inspection chamber.
Branches should enter the main channel discharging in the direction of flow at an angle of no
more than 45° to the main flow subject, to the provisions above. Where sharper angles are to be
accommodated, bends of up to a maximum 45° may be sited immediately outside the chamber. Bends
may also be sited inside the chamber, however in these cases they should be in the form of open
channels to facilitate access by equipment.
Side branches of diameters up to, and including, DN 150 should discharge to the main channel in the
direction of flow, preferably at half pipe level or above.
A branch with a diameter greater than DN 150 should be set with the soffit level with that of the main
drain. However where a branch is the same diameter as the main branch, but has significantly lower
flow, the branch pipe should be set so that the invert of the branch pipe is 50 mm above the invert of
the main pipe. At a change in diameter of drains or sewers and where conditions permit, the soffits of
the pipes should be at the same level.
NA.12.5.3 Dimensions
The minimum plan dimensions of the opening into the pipe from an inspection should be sufficient to
provide the minimum entry radius through the access shaft into any pipe specified in Table NA.21. The
horizontal dimension of the shaft should be equal to the nominal diameter of the main pipe subject to
a minimum of 180 mm (see Figure NA.15).
Table NA.21 – Minimum entry radii from inspection chambers into pipes up to DN 300
Minimum entry radius
[mm]
Nominal internal diameter
of pipe
[mm]
100
150
225
300
Type 1
400
500
600
750
Type 2
500
600
750
850
A lead-in should be provided where rods or jetting hoses or cables are likely to be damaged due to the
tight radius at the pipe entry.
Where available, bends should be made with curved bend fittings. The radius of the centreline of the
bend should not be less than the nominal internal diameter of the pipe. Where curved bend fittings
are not available, mitre bends may be used. The angle of each mitre should not be more than 22.5°
where the nominal internal diameter of the pipe is less than 600 mm and not more than 45˚ where the
nominal internal diameter is of the pipe is greater than or equal to 600 mm.
Inspection chambers are not intended for entry by personnel and therefore the dimensions of the
opening to chambers more than 1 metre in depth should be restricted to ensure that personnel entry
is not possible. To deter personnel entry, the clear opening should be no larger than 300 mm × 300 mm
or 350 mm diameter.
Table NA.22 gives dimensions for commonly used chambers that meet these requirements, however
other types of chamber meeting the above requirements may also be used.
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BS EN 752:2008
minimum
entry radius
minimum
entry radius
minimum
entry radius
Figure NA.15 – Inspection chambers
Table NA.22 — Recommended dimensions for the construction of new rodding
points, access fittings and inspection chambers (No personnel entry)
Type of access
Minimum nominal internal
dimensions a)
Clear opening size
Remarks
Rectangular
Circular diameter
Rectangular
Circular diameter
length and width
length and width
[mm]
Rodding point
—
[mm]
Preferably same
size as drain but
not less than
DN 100
Inspection
chamber
(Type 1)
150 x 100 c)
180 c)
300 x 300
300
Inspection
chamber
(Type 2)
225 x 100 c)
180 c)
450 × 450
450
[mm]
[mm]
—
Same size as
pipework b)
Minimum size
20 mm less than
the size of the
chamber subject
to a maximum
of 300 × 300 d)
where the depth
of the chamber
is greater than
1.0m
Minimum 20 mm
size less than the
diameter of the
chamber subject
to a maximum
of 350 d) where
the depth of
the chamber is
greater than
1.0m
a)
These sizes apply to straight-through pipes; larger sizes should be used at turning chambers or chambers with several
side branches.
b)
The clear opening may be reduced by 20 mm in order to provide proper support for the cover and frame.
c)
Where entry radius is provided in accordance with Table 21.
d)
A larger clear opening cover may be used in conjunction with a restricted access. Restricted to inspection and remotely
operated equipment – no personnel entry. Max size imposed to prevent personnel entry.
NA.12.6
NA.12.6.1 Access to manholes
A permanent means of access and egress can be provided by ladders, stairways or steps. Where ladders
or steps are in use, a means of fall prevention should also be provided for those using the ladders
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or steps. Due allowance should be made for facilitating the use of industry standard fall prevention
equipment when designing and constructing manholes.
Facilities should be included to provide hand holds during the transition of a person from being partly
above ground to wholly in the manhole. Alternatively, when access is by means of steps, handholds
fulfilling the same function, may be provided. Stairs should be fitted with proper guardrails.
Where frequent access is required, a staircase should be provided to at least the lowest dry landing.
A landing or half-landing should be provided at vertical intervals not exceeding 6 m in the manhole.
Landings provide a safe working platform within a manhole access system and should conform to the
current statutory requirements for safe working platforms at height.
In order to deter unauthorized access, some manholes are not fitted with permanent ladders or steps.
In such cases, personnel are normally winched in to and out of the manhole, however, an alternative
means of rapidly removing personnel including casualties from the manhole, should be provided for
use in an emergency.
Deep manholes should be provided with rest chambers, or platforms not more than 6 m apart vertically.
Access openings in successive landings should be staggered to limit the height of an accidental fall from
the access ladder. Guardrails should be provided on each landing at the base of the ladder to ensure
that it is not possible to step inadvertently from the bottom of one ladder into the access opening for
the next ladder down or through any opening in an adjacent landing slab edge guardrail. Separate
openings should be provided, suitably protected by trap doors that can be secured in the open position,
directly below each other for the movement of materials, tools, safety devices, casualties and for the
use in pumping/jetting and other maintenance operations. Openings in guardrails should be barriered
off at top- and mid-rail level with a self-closing gate or equivalent, which does not depend on human
intervention to shut. In this context, hooks and chains have been proved to form an ineffective barrier.
NA.12.6.2 Layout
Where pipes connect at a manhole the branch flows should merge with the main channel using swept
channels. Where available, preformed channels should be used. The horizontal angle between any
incoming pipe and the outgoing pipe should not be less than 90°.
Branches should enter the main channel discharging in the direction of flow at an angle of no more than
45° to the main flow subject to the provisions above. Where sharper angles are to be accommodated,
bends of up to a maximum 45° may be sited immediately outside the chamber. Bends may also be sited
inside the chamber; however in these cases they should be in the form of open channels to facilitate
access by equipment.
Bends may also be accommodated using a curved open channel within the manhole. Bends with an
angle of not more than 45° may be used immediately outside manholes on the inlet, the outlet or both
pipes. On pipes with a nominal internal diameter greater than 225 mm, a bend outside a manhole is
only permitted at one end of a pipe. Where bends occur outside manholes, this can restrict access for
CCTV surveys in small diameter pipes.
Side branches of diameters up to, and including, DN 150 should discharge to the main channel in the
direction of flow, preferably at half pipe level or above.
A branch with a diameter greater than DN 150 should be set with the soffit level with that of the main
drain. At a change in diameter of drains or sewers and where conditions permit, the soffits of the pipes
should be at the same level.
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The main channel should extend the whole length of the chamber, comprising a half-round section plus
vertical benching from the top edge of the half-round section to a height of not less than that of the
soffit of the outlet where it should be rounded off to a radius of about 25 mm and sloped upwards to
meet the wall of the chamber. Where the connecting angle is greater than 45°, three-quarter section
bends should be used. Vertical and side benching should be shaped so as to contain the flow without
permitting fouling and to facilitate the cleaning of branches.
Where a drain or sewer connects with another at a significantly lower level, a manhole may be built
on the lower pipe incorporating a vertical or nearly vertical drop pipe. The drop pipe may be outside
the chamber and, in which case, it should be encased in concrete, or supported inside the chamber, in
which case, the chamber should be suitably enlarged. Access should be provided to the higher pipe and
to the vertical drop pipe for inspection and maintenance.
Where the difference in level is less than 1,8 m, a 45° ramp is often preferable to a vertical drop pipe.
Backdrops should terminate at their lower end with a bend to discharge into the main channel at 45°
or less. The bend at the base should be properly supported.
Consideration should be given to incorporating some form of energy dissipation for backdrops on
drains and sewers larger than DN 450 and for deep drops.
In manholes, the benching slope should not be flatter than 1:30, in order to provide a working surface.
NA.12.6.3 Dimensions
NA.12.6.3.1 General
Manhole size is determined by the need for safe access and egress and the provision of adequate
working space along with its depth, size of pipe, number of branches and change of direction. See
Table NA.23 for minimum dimensions.
Where ladders or step rungs are used, a minimum width of benching of 450 mm should be provided
between the ladder rungs and the channel to provide a landing area. Pipes and access covers may be
positioned off-centre to facilitate access and to maximize the working space.
For manholes with depth from cover level to pipe soffit of less than 1,5 m giving access to pipes not
exceeding DN 450, the width should allow at least 225 mm wide benching on each side. In all other cases,
the width should allow at least 325 mm on one side of the chamber and at least 450 mm on the other.
In shallow manholes, consideration should be given to decreasing the level of the benching to not less
than half pipe height in order to give more adequate headroom.
A space ≥ 900 mm should be provided on the benching at the base of a ladder or run of steps. For
channel widths less than, or equal to, 450 mm, at least 450 mm of this should be provided between
the base of the ladder and the channel (see Figure NA.16). For channel widths greater than 450 mm,
this should be provided on the same side of the channel as the steps. This is usually most economically
accommodated by placing the ladder normal to the channel (see Figure NA.17).
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225 mm
minimum
900 mm
minimum
450 mm
minimum
BS EN 752:2008
Figure NA.16 — Working space around a ladder or steps (pipe size ≤ DN 450)
325 mm
minimum
450 mm
minimum
900 mm
minimum
Figure NA.17 — Working space around a ladder or steps (pipe size > DN 450)
NA.12.6.3.2 Sizes of shafts and entries
Manholes deeper than 3 m to soffit may be constructed with an access shaft rather than extending the
chamber to ground level. Access shafts should have a clearance of approximately 900 mm between the
steps or ladder and the back of the shaft, see Table NA.23. Consideration should be given to the size
of equipment likely to be required to use the shaft; but shafts should not be oversized as this would
prevent the back of the shaft being used to break a fall.
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NA.12.6.3.3 Landings
The landings and platforms and access opening arrangements should be of adequate size to
accommodate at least two operatives with safety harnesses; and to minimize the risk of falling, open
edges should be provided with double guardrails (i.e. top- and mid-rail) and toe boards.
Not less than 900 mm room should be provided on any landing between the face of the steps and any
wall or handrail.
NA.12.6.3.4 Steps
Manhole steps should be Type D Class I double steps conforming to BS EN 13101:2002 with a minimum
width of tread of 320 mm.
Manhole steps should be built into the wall at regular height intervals of between 230 mm and 300 mm.
The top step should be not more than 675 mm below the surface; the lowest not more than 300 mm
above the benching.
Manhole steps should not be used for access/egress in manholes deeper than 3,0 m. Manhole steps
should be built into the wall at regular height intervals of between 230 mm and 300 mm. The top step
should be not more than 675 mm below the surface; the lowest not more than 300 mm above the
benching.
Where covers larger than the minimum size given in Table NA.23 are used, one or more handholds
should be built into the sides of the shaft beneath the cover frame.
Not less than 150 mm foot room should be provided behind steps when measured at the centre of
the step.
Steps should not intrude into the flow. Recessed steps or toe holes should be used in association with
hand holds.
NA.12.6.3.5 Ladders
Fixed, corrosion resistant ladders (or stairs) should be used for depths over 3,0 m.
Ladders should conform to BS EN 14396:2004 and should not rise more than 6 m without provision of
an intermediate platform, which should preferably break the line of the ladder. Not less than 200 mm
foot room should be provided behind ladders. Stringers should be adequately supported from the
manhole wall at intervals of not more than 3 m. Stringer supports should not be built into the wall but
bolted to built-in cleats to facilitate renewal.
Fixed ladders should not protrude into the flow. Recessed toe holes in association with hand holds, or
movable sections of ladder should be used.
The top rung should be within 675 mm of the surface and ladders should be positioned relative to the
access, so that the minimum clear opening is not obstructed.
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>3,0
≥1,5
<1,5
(mm)
(mm)
1200 × 800
900 × 800
Ladder
Winch
900
1200
1050
600 × 600
600 × 600
The larger of 1800
or (DN + 900)
1800 × (DN + 775)
>900
1050 × 800
600 × 600
1200
1200
1350
1500
1800
1200 × 1000
1200 × 1075
1350 × 1225
1500 × 1475
1800 × 1675
≤ 225
300
375 – 450
500 – 700
750 – 900
Steps
1200 × 675
The larger of 1800
or (DN + 900)
1800 × (DN + 775)
> 900
750 × 675 e) f)
1200 × 675 h)
1200 × 675
1200 × 675
1200 × 675
1200 × 675
(mm)
600
600
600
na g)
(mm)
Circular diameter
Min. clear opening size
Rectangular –
length and width
750 × 675 c)
1200 × 675
1200 × 750
1350 × 900
1500 × 1150
1800 × 1350
1000 d)
1200
1200
1350
1500
1800
Circular – diameter
Rectangular –
length and width
Min. internal dimensions a)
≤ 150
225
300
375 – 450
500 – 700
750 – 900
DN largest
Depth to pipe
pipe in
soffit from
manhole/means
cover level
of descent into
(m)
shaft
Winch only – no steps or ladders
(permanent or removable)
Min. clear space between the
ladder/steps and the opposite face
of the shaft should be approx.
900 mm.
Generally in accordance with Safe
Work in Confined Spaces – Health
and Safety Commission [29].
Larger opening size is required for
manholes at shallower depths to
permit standing/crouching.
Where a ladder is provided the
minimum size should be increased
see NA.4.3.2 and NA.4.10.2.
Remarks
See footnote c.
May be reduced to 600 mm × 600 mm or 600 diameter where the configuration of the manhole chamber permits a safe system of work.
May be reduced to 600 mm × 600 mm diameter where required by highway loading considerations, subject to safe system of work being specified.
Not applicable due to working space needed.
See footnote f.
Minimum height of chamber in shafted manhole 2m from benching to underside of reducing slab.
e)
f)
g)
h)
i)
c)
d)
Chamber with a removable cover constructed on a drain or sewer to permit entry by personnel [BS EN 752, 3].
The minimum size of any manhole serving a more than one property should be 1200 mm diameter or 1200 mm × 675 mm rectangular.
b)
These sizes apply to straight-through pipes, for turning chambers or chambers with several side branches or where specific maintenance requirements are necessary,
e.g. disconnecting traps the minimum sizes should be increased.
a)
Manhole shaft i)
Manhole b)
Type of access
Table NA.23 — Recommended dimensions for the construction of new manholes and manhole shafts (with personnel entry)
BS EN 752:2008
BS EN 752:2008
NA.12.6.4 Inspection chamber and manhole construction
NA.12.6.4.1 General
Inspection chambers and manholes should be watertight, durable and designed to minimize the risk
of blockage.
Inspection chambers, manholes and other pipeline structures should be designed to carry the worst
combination of superimposed and ground loading. Foundations should be designed to carry all the
imposed loads. The chamber walls and base should also be designed to take into account any lateral
loading and/or hydrostatic upthrust and to prevent flotation.
Where lampholes and deep maintenance shafts are used, they should be constructed in such a way that
traffic loads on the cover are not transmitted onto the shaft, which could otherwise be pushed into
the drain or sewer, e.g. by bedding the cover and frame on a concrete slab separated from the shaft
by sleeving.
Where a pipeline is built into any manhole or inspection chamber, or other structure such as a
groundbeam or concrete surround, some differential settlement between the pipeline and structure is
to be expected.
To avoid the consequent high shear loads on the pipe built-in to the structure, the first flexible joint
on the pipeline should be provided as close to the face of the structure as practicable. This should be
within 150 mm for pipe diameters less than 300 mm.
A short length “rocker” pipe should be laid next before any full length pipes are used, to isolate the
pipeline from small relative movements caused by differential settlement. The maximum length of the
rocker pipe should be as shown in Table NA.24. Short length pipes with pre-formed joints are available
from manufacturers or plain-ended pipes may be cut to size.
Table NA.24 — Recommended maximum length of rocker pipes
Nominal pipe diameter
Maximum length
[m]
< 300
0,6
301–450
0,75
451–750
1,00
> 750
1,25
For pipe diameters greater than DN 1500, consideration should be given to the angular performance
of the joints of short rocker pipes subject to significant settlement.
Where large differential settlements are anticipated, e.g. in waterlogged soils, peat silt or made
ground, the number of short length pipes should be increased. Shallow gradients should be avoided in
this situation, in order to minimize the possibility of deposition of solids.
Non-prefabricated inspection chambers and manholes that are constructed in situ should be roofed
either by a concrete slab or by engineering brickwork arches and corbelling, with lintels as necessary,
designed to resist dead and superimposed loads (see BS 5400-2:2006). In situ slabs should not be less
than 150 mm thick.
Cover frames should be bedded on one, two or three courses of engineering brickwork or precast
concrete adjusting units. The clear opening of the cover should be not less than the clear opening in
the cover slab or shaft, if applicable.
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Where practicable, the channel should be of the same material as the drain or sewer. Where this is not
practicable, pre-formed channels of other materials or concrete with a granolithic finish may be used.
Pipes should be built into manholes as construction proceeds.
All manholes on drains and sewers of DN 600 diameter and over should be provided with a safety
chain or bar for placing across the mouth of the outgoing sewer when operatives are at work. Double
guardrails (i.e. a top rail and mid-rail) should be provided on the edges of benching and at platforms,
etc. from which a person might fall into the sewer and toe-holes should be provided in the benching
to allow access into the drain or sewer.
Inspection chambers and manholes in agricultural land should be sited, if possible, near to hedges or
other boundaries of fields.
In low-lying agricultural land the possibility of flooding should be taken into account. Consideration
should be given to building the chamber up to about 600 mm above natural ground surface and
mounded on all sides with earth. Alternatively, the chamber may be covered with a concrete slab, the
top of which should be at least 600 mm below ground level to avoid conflict with agricultural activities.
The burying of covers should be avoided, especially at changes of direction. However, wherever a
chamber is slabbed over (where a cover cannot be allowed on, or near, the surface), carefully referenced
measurements need to be made to some fixed points to enable them to be located quickly and accurately.
Materials for construction of inspection chambers and manholes include:
a)
engineering brickwork;
b) concrete, in situ and precast;
c)
plastics;
d) vitrified clay;
e)
cast iron.
NA.12.6.4.2 Precast concrete
An in situ concrete surround is not normally required for inspection chambers and manholes unless
installed in areas of unstable ground, under conditions of flotation or where subjected to exceptional
or eccentric loads (e.g. construction loads), in which cases a 150 mm surround of at least 20 N/mm2
concrete should be provided; any joints should be staggered with the precast concrete joints
Segmental manholes, especially those sunk as caissons, should be provided with grout holes so that
voids can be filled.
NA.12.6.4.3 Brickwork
Chambers and shafts should normally be built with solid engineering bricks in English bond but resistance
to water penetration can be increased if the brickwork is built in “water” (“manhole”) bond. The wall
thickness should be adequate to resist external pressures due, e.g. to soil and ground water but in any
case not less than 200 mm. Where ground water pressures are continuously high, double leaf (collar
jointed) construction (see BS 5628-1) or tanking should be used to maintain water pressure resistance.
In granular soils above the water table, inspection chambers 900 mm or less in depth (unless in roads or
other areas subject to vehicular traffic) may be built in brickwork not less than 100 mm thick.
Joints should be filled with well compacted mortar 4 mm to 6 mm thick, completely filled and flushed
pointed as the work proceeds.
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BS EN 752:2008
Pipes through chamber walls should be bedded on mortar. DN 300 or larger pipes should have either a
one-brick relieving arch over the pipe to the full thickness of the brickwork, or a concrete lintel or other
effective means of relieving the load.
NA.12.6.4.4 In situ concrete
For chambers constructed of in situ concrete the thickness of the walls should be not less than that
stated for brick manholes (see NA.12.6.4.3) and the concrete should be in accordance with BS 8500. The
design should be in accordance with BS EN 1992-2 or BS EN 1992-3.
NA.12.6.5 Channels and benching
NA.12.6.5.1 General
Where the benching is not precast or pre-formed, the main and branch channels should be bedded
and jointed in 1:3 cement mortar, and in situ benching floated to a hard smooth surface with a high
strength concrete topping laid monolithic with the benching. To ensure that the channel and branch
junctions are properly supported, the bedding and the benching should be laid in a single operation.
Where plastics channel sections are used, special care should be exercised to ensure adequate bonding
with the base.
NA.12.6.5.2 Pre-formed thermoplastics
The provisions of NA.12.6.5.1 need not apply for inspection chambers and manhole bases, which are preformed in thermoplastics materials. These prefabricated bases provide improved hydraulic conditions
resulting from main and branch channel geometry and configurations that incorporate a gradient
throughout their length.
NA.12.6.5.3 Catchpits
Catchpits are chambers on surface water drains and sewers installed to retain silt and constructed as
manholes but without benching. They are also often used on sub-soil drains, especially at the point of
connection with a surface water drain or sewer. The chamber floor is usually 450 mm below the invert
of the outlet to form a sump and the invert of the inlet is usually 25 mm above the invert of the outlet
to form a cascade for improved hydraulic efficiency.
NA.13 Relevant authorities
NA.13.1 Introduction
The different legislative arrangements in various European countries make it impossible for an EN to
refer to statutory authorities by name. EN 752 therefore refers to such organizations using the term
“relevant authority”.
This national annex lists the names of those relevant authorities, which have powers relevant to this
standard. It gives their name and function together with the principal legislation relating to EN 752
and any published guidance. The lists of legislation and published guidance are not exhaustive and
other publications could be relevant.
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BS EN 752:2008
Where the term “Local Authority” is used, unless otherwise stated, this should be taken to mean:
a)
in England: the District, Metropolitan District, London Borough or (in some areas) Unitary Council;
b) in Wales: the County or County Borough Council;
c)
in Scotland: the Unitary, or Island Council;
d) in Northern Ireland: the District Council.
In some parts of England, functions are split between County Councils and District Councils. In these
areas, where a function is carried out by the County Council this is indicated.
The reference documents include dates, however, users should ensure that they are using the most up
to date edition.
NA.13.2 Sewerage Undertaker
NA.13.2.1 Relevant functions
Provision of sewerage services including the design, construction, maintenance and operation of public
sewer systems.
NA.13.2.2 England and Wales
The Sewerage Undertaker is a company appointed by the Secretary of State for the Environment food
and Rural Affairs to carry out sewerage functions in an area.
Guidance is available in the following published documents:
— Sewers for Adoption [1];
— Civil Engineering Specification for the Water Industry [7].
NA.13.2.3 Scotland
Scottish Water.
Guidance is available in the following published documents:
— Sewers for Scotland [2];
— Civil Engineering Specification for the Water Industry [7].
NA.13.2.4 Northern Ireland
The Sewerage Undertaker is a company appointed by the The Department for Regional Development
(Northern Ireland).
Guidance is available in the following published documents:
— Civil Engineering Specification for the Water Industry [45].
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NA.13.3 Building control
NA.13.3.1 Relevant functions
To ensure a satisfactory drainage system from a building to a point of discharge.
NA.13.3.2 England and Wales
The Local Authority (Building Control Department). Certain functions can be delegated to approved
inspectors.
Guidance is available in the following published document:
— Building Regulations 2000, Approved Document H – Drainage and waste disposal [3].
NA.13.3.3 Scotland
The Local Authority (Building Control Department).
Guidance is available in the following published documents:
— Building (Scotland) Regulations 2005 Technical Handbook Domestic [4];
— Building (Scotland) Regulations 2005 Technical Handbook Non-domestic [5].
NA.13.3.4 Northern Ireland
The Local Authority (Building Control Department).
Guidance is available in the following published document:
— Technical Booklet N: Drainage, ISBN 0-337-08225-1 [6].
NA.13.4 Water pollution control
NA.13.4.1 Relevant functions
Protection from pollution of all receiving water including groundwaters. Control of effluent discharge
into rivers and into other receiving waters.
NA.13.4.2 England and Wales
The Environment Agency.
Guidance is available in the following published documents:
— Urban Pollution Management Manual [33];
— The Urban Waste Water Treatment (England and Wales) Regulations 1994: a Guidance Note [34];
— Environment Agency, Policy and Practice for Protection of Groundwater GP3 Part 4 (Under revision)
[46];
— Interim Code of Practice for Sustainable Drainage Systems [9].
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NA.13.4.3 Scotland
The Scottish Environmental Protection Agency.
Guidance is available in the following published document:
— Urban Pollution Management Manual [33].
NA.13.4.4 Northern Ireland
The Department of the Environment (Northern Ireland) – Environment and Heritage Service.
NA.13.5 Rivers and land drainage
NA.13.5.1 Relevant functions
Overall supervision of the management of rivers and flood defences.
NA.13.5.2 England and Wales
The principal land drainage authority in England and Wales is the Environment Agency. Internal
Drainage Boards and local authorities also have some land drainage functions.
NA.13.5.3 Scotland
The principal land drainage authority in Scotland is the Scottish Environmental Protection Agency
(SEPA). Local authorities also have some land drainage functions.
NA.13.5.4 Northern Ireland
The principal land drainage authority in Northern Ireland is the Environment and Heritage Service for
Northern Ireland.
NA.13.6 Waste regulation
NA.13.6.1 Relevant functions
The control of disposal of waste.
NA.13.6.2 England and Wales
The Environment Agency.
NA.13.6.3 Scotland
The Scottish Environmental Protection Agency.
NA.13.6.4 Northern Ireland
The Department of the Environment (Northern Ireland) – Environment and Heritage Service.
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NA.13.7 Environmental health
NA.13.7.1 Relevant functions
Responsible for protecting the health of the public including nuisance caused by noise and by public
and defective private sewers and drains.
NA.13.7.2 England, Wales, Scotland and Northern Ireland
The Local Authority (Environmental Health Department).
NA.13.8 Highway authority (roads authority in Scotland and Northern Ireland)
NA.13.8.1 Relevant functions
The construction and maintenance of highways including highway drainage, regulation of traffic and
regulation of work carried out in highways.
NA.13.8.2 England
Trunk roads: The Highways Agency (England).
Other roads: Local Authority.1
Guidance is available in the following published documents:
— Manual of contract documentation for highway works. Vol. 1 Specification for highway works [42];
— Design Manual for Roads and Bridges [24];
— Specification for the Reinstatement of Openings in Highways [47];
— Measures Necessary where Apparatus is Affected by Major Works (Diversionary Works) [48];
— Code of Practice for Inspections [49];
— Safety at Street Works and Road Works – A Code of Practice [50];
— Code of Practice for the Co-ordination of Street Works and Works for Road Purposes and Related
Matters [51];
— Code of Practice on Recording of Underground Apparatus in Streets [52].
The Department of Transport publishes other advice notes and Technical Standards from time to time
and its publications list should be consulted.
1
In those parts of England with separate County and District Councils this is a County function.
63
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BS EN 752:2008
NA.13.8.3 Wales
Trunk roads: Welsh Assembly Government (Wales).
Other roads: Local Authority.2
Guidance is available in the following published documents:
— Manual of contract documentation for highway works. Vol. 1 Specification for highway works [42];
— Design Manual for Roads and Bridges [24];
— Specification for the Reinstatement of Openings in Highways [47];
— Measures Necessary where Apparatus is Affected by Major Works (Diversionary Works) [48];
— Code of Practice for Inspections [49];
— Safety at Street Works and Road Works – A Code of Practice [50];
— Code of Practice for the Co-ordination of Street Works and Works for Road Purposes and Related
Matters [51];
— Code of Practice on Recording of Underground Apparatus in Streets [52].
The Department of Transport publishes other advice notes and Technical Standards from time to time
and its publications list should be consulted.
NA.13.8.4 Scotland
Trunk roads: The Scottish Executive.
Other roads: The Local Authority.
Guidance is available in the following published documents:
— Manual of contract documentation for highway works. Vol. 1 Specification for highway works [42];
— Design Manual for Roads and Bridges [24].
The Codes of Practice listed in NA.13.8.2 also apply to Scotland.
NA.13.8.5 Northern Ireland
The Department for Regional Development (Northern Ireland) – Roads Service. Guidance is available in
the following published documents:
— Manual of contract documentation for highway works. Vol. 1 Specification for highway works [42];
— Design Manual for Roads and Bridges [24].
2
64
174
In those parts of England with separate County and District Councils this is a County function.
BS EN 752:2008
NA.13.9 Occupational health and safety
NA.13.9.1 Fundamental statutory principles
Legal obligations are placed on employers to ensure, so far as reasonably practicable, the health,
safety and welfare of all employees. These legal obligations include the provision and maintenance
of safe plant and safe systems of work and the provision of the information, instruction training and
supervision, which is necessary to ensure the health and safety of employees and of others who could
be affected by the work activity.
NA.13.9.2 England, Wales and Scotland
The Health and Safety Executive publish the following guidance documents:
— Approved Codes of Practice and HSE guidance supporting the above Regulations can be found at
http://www.hsebooks.com
— Other relevant guidance is published by the engineering institutions and trade organizations.
NA.13.9.3 Northern Ireland
The Health and Safety Executive for Northern Ireland is sponsored by the Department of Enterprise,
Trade and Investment The legislation is identical in its requirements to that for Great Britain. Some
legislation listed in NA.8.2 applies throughout the UK. Where that is not the case, the regulations are
similar to those for Great Britain but incorporate the text “(Northern Ireland)” in their titles.
Northern Ireland uses the same guidance as for Great Britain.
NA.13.10 Planning authority
NA.13.10.1 Relevant functions
Responsible for controlling development in an area.
NA.13.10.2 England and Wales
The Local Authority (Planning Department).
Guidance is available in the following published documents:
— planning policy statements are available at http://www.planningportal.gov.uk
NA.13.10.3 Scotland
The Local Authority (Planning Department).
Scottish planning policy documents are available at
http://www.scotland.gov.uk/Topics/Planning/PolicyLegislation/Policy
NA.13.10.4 Northern Ireland
The Department of the Environment (Northern Ireland) Planning Service.
Planning policy statements are available at http://www.planningni.gov.uk/AreaPlans_Policy/PPS/PPS.htm
65
175
BS EN 752:2008
Bibliography
[1] Sewers for Adoption, Water Services Association, 6th Edition 2006, WRc. ISBN 0 8989 20 8.
[2] Sewers for Scotland, 2nd Edition 2007, WRc. ISBN 978 1898920 601.
[3] Building Regulations 2000 Approved Document H – Drainage and waste disposal, 2002 Edition
(updated 2006), HMSO. ISBN 978 1 85946 208 9. Also available for download at http://www.
planningportal.gov.uk
[4] Technical Handbook to Building (Scotland) Regulations 2004. Technical Handbook – Domestic.
ISBN 0 9546292 2 1. Also available for download at http://www.sbsa.gov.uk
[5] Technical Handbook to Building (Scotland) Regulations 2004. Technical Handbook – Non-domestic.
ISBN 0 9546292 3 X. Also available for download at http://www.sbsa.gov.uk
[6] DOE Technical Booklet N: 1990 – Drainage. Available at http://www.dfpni.gov.uk/drainage.pdf
[7] HR WALLINGFORD and D I H BARR. Tables for the hydraulic design of pipes, sewers and channels:
8th edition (2 volume set) Thomas Telford Ltd. London 2006. ISBN 0727733850.
[8] WRc Sewerage Rehabilitation Manual. 4th Edition WRc 2001. ISBN 1 898920 40 0. Available at
http://www.wrcplc.co.uk/srm (Note a revision is in preparation.)
[9] NATIONAL SUDS WORKING GROUP. Interim Code of Practice for Sustainable Drainage Systems,
National SUDS Working Group, July 2004. ISBN 0 86017 904. Also available for download at http://
www.environment-agency.gov.uk
[10] DEPARTMENT OF COMMUNITIES AND LOCAL GOVERNMENT. Planning Policy Statement 25:
Development and Flood Risk PPS25, Communities and Local Government, 2006.
ISBN 978 0 11 753974 7. Also available for download at http://www.planningportal.gov.uk
[11] Design and Analysis of Urban Storm Drainage: The Wallingford Procedure Volume 1 Principles,
methods and practice. National Water Council, Standing Technical Committee Reports No. 28
1981. Available from HR Wallingford. http://www.hrwallingford.co.uk/index.aspx
[12] Design and Analysis of Urban Storm Drainage: The Wallingford Procedure Volume 3 Maps.
National Water Council, Standing Technical Committee Reports No. 30 1981. Available from HR
Wallingford.
[13] Design and Analysis of Urban Storm Drainage: The Wallingford Procedure Volume 4 The modified
Rational method. National Water Council, Standing Technical Committee Reports No. 30 1981.
Available from HR Wallingford. http://www.hrwallingford.co.uk/index.aspx
[14] Environment Agency Groundwater Source Protections Zone Maps. http://www.environment-agency.
gov.uk/maps/info/groundwater
[15] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). Infiltration
Drainage – Manual of Good Practice. CIRIA Report 156, 1996. ISBN 978 0 86017 457 8. Available at
http://www.ciria.org/acatalog/R156.html
[16] BUILDING RESEARCH ESTABLISHMENT. Soakaway Design. BRE Digest 365 1991. ISBN 1 86081 604 5.
Available at http://www.brebookshop.com/details.jsp?id=844
[17] WRc, Sewerage Detention Tanks – A Design Guide, WRc 1997. ISBN 1 898920 38 9.
[18] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). M J Hall, D L
Hockin and J B Ellis. Design of Flood Storage Reservoirs, 1993. ISBN 978 0 86017 393 9.
[19] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). Source control
using constructed pervious surfaces. Hydraulic, structural and water quality performance issues.
CIRIA Report C582, 2002. Available for download at http://www.ciria.org/acatalog/c582.pdf
[20] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). The SUDS
Manual. CIRIA Report C697, March 2007. ISBN 978 0 86017 697 8 Available for download at http://
www.ciria.org/downloads.htm
66
176
BS EN 752:2008
[21] BETTESS R. Designing for exceedance in urban drainage – Good practice. CIRIA Report C635, 2006.
Available for download at http://www.ciria.org/acatalog/c635.pdf
[22] SPALIVIERIO F, MAY R W. Spacing of Road Gullies: Project report hydraulic performance of BS EN 124
gully gratings. SR533 1999. Available at http://www.hrwallingford.co.uk/index.aspx
[23] ESCARAMEIA M. Hydraulic design of paved areas SR606 November 2002. Available at http://www.
hrwallingford.co.uk/index.aspx
[24] THE HIGHWAYS AGENCY, THE SCOTTISH EXECUTIVE, THE NATIONAL ASSEMBLY FOR WALES, THE
DEPARTMENT FOR REGIONAL DEVELOPMENT NORTHERN IRELAND. Design Manual for Roads and
Bridges Volume 4, Section 2 Drainage. Available from http://www.standardsforhighways.co.uk
[25] WHIFFIN, AC, YOUNG, CP. Drainage of level or nearly level roads. Transport and Road
Research Laboratory Report LR602, 1973. Available at http://www.trl.co.uk/store/report_detail.
asp?srid=4893&pid=173
[26] ESCARAMEIA M, GASOWSKI Y, MAY RWP, LO COSCIO A. Hydraulic Capacity of Drainage Channels
SR581 February 2001. Available at http://www.hrwallingford.co.uk/index.aspx
[27] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). Erosion of Sewers
and Drains. CIRIA Report R014M, 1968. ISBN 978 0 901208 21 7.
[28] CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). Design of sewers
to control sediment problems, CIRIA Report 141. ISBN 086017 443 3.
[29] HEALTH & SAFETY COMMISSION. Safe work in confined spaces, Approved Code of Practice,
Regulations and Guidance HSE Books 1997. ISBN 0 7176 1405 0.
[30] MINISTRY OF HOUSING AND LOCAL GOVERNMENT – Technical Committee on Storm Overflows
and the Disposal of Storm Sewage, Final Report, 1970.
[31] BALMFORTH D J, SAUL A J, and CLIFFORDE IT. Guide to the Design of Combined Sewer Overflow
Structures. Foundation for Water Research. FR0488, 1994.
[32] WaPUG – The Design of CSO Chambers to Incorporate Screens Version 3 November 2006 WaPUG.
http://www.wapug.org.uk
[33] FOUNDATION FOR WATER RESEARCH. UPM Manual – A Planning Guide for the Management of
Urban Wastewater Discharges During Wet Weather. Foundation for Water Research. FR/CL002,
1998.
[34] The Urban Waste Water Treatment (England and Wales) Regulations, 1994: Working document for
dischargers and regulators: a Guidance note. DETR and the Welsh Office, 1997.
[35] The Urban Waste Water Treatment (Scotland) Regulations 1994: A working document for
dischargers and regulators. A guidance note issued by the Scottish Office Agriculture, Environment
and Fisheries Department February 1998. Available for download at http://www.sepa.org.uk/
guidance/index.htm#water
[36] The Urban Waste Water Treatment Regulations (Northern Ireland) 1995: A working document
for dischargers and regulators. The Department Of The Environment (Northern Ireland) 1999.
Available for download at http://www.ehsni.gov.uk/water/regulation_of_discharges_industrial/
reg_sewage.htm
[37] COUNCIL OF THE EUROPEAN COMMUNITIES. Directive Concerning the Quality of Bathing Water
(76/160/EEC).
[38] COUNCIL OF THE EUROPEAN COMMUNITIES. Directive Concerning the Quality of Shellfish Waters
(79/923/EEC).
[39] COUNCIL OF THE EUROPEAN COMMUNITIES Directive 2006/7/EC of the European Parliament and
of the Council concerning the management of bathing water quality and repealing Directive
76/160/EEC.
[40] Materials selection manual for sewers, pumping mains and manholes. Foundation for Water
Research, Marlow 1993.
67
177
BS EN 752:2008
[41] Specification for bedding and sidefill materials for buried pipelines, WIS 4-08-02. Available for
download at http://www.wis-ign.org/downloads/WIS%204-08-02.pdf
[42] HIGHWAYS AGENCY, THE SCOTTISH EXECUTIVE, THE NATIONAL ASSEMBLY FOR WALES, THE
DEPARTMENT FOR REGIONAL DEVELOPMENT NORTHERN IRELAND. Manual of Contract Documents
for Highway Works Volume 1 Specification for Highway Works. HMSO. Available for download at
http://www.standardsforhighways.co.uk
[43] Concrete in aggressive ground (Special Digest 1), BRE 2005. ISBN 1 86081 754 8. Available at http://
www.brebookshop.com/details.jsp?id=149036
[44] Use of oil separators in surface water drainage systems Pollution prevention guideline no.
3 April 2006. Available for download at http://publications.environment-agency.gov.uk/pdf/
PMHO0406BIYL-e-e.pdf
[45] Civil Engineering Specification for the Water Industry, UKWIR, 6th Edition 2004, WRc.
ISBN 898920 51 6.
[46] Environment Agency, Groundwater Protection: Policy and Practice (GP3), Part 4 (under revision).
[47] DEPARTMENT FOR TRANSPORT. Specification for the Reinstatement of Openings in Highways 2002.
ISBN 0 11 552538 6. Available for download at http://www.dft.gov.uk/pdf/pgr/roads/network/local/
streetworks/cop/roo/
[48] DEPARTMENT FOR TRANSPORT. Measures Necessary where Apparatus is Affected by Major Works
(Diversionary Works). ISBN 0 11 551149 0.
[49] DEPARTMENT FOR TRANSPORT. Code of Practice for Inspections 2nd Edition 2002.
Available for download at http://www.dft.gov.uk/pgr/roads/network/local/streetworks/cop/
codeofpracticeforinspections
[50] DEPARTMENT FOR TRANSPORT. Safety at Street Works and Road Works – A Code of Practice
2nd Edition 2002. Available for download at http://www.dft.gov.uk/pdf/pgr/roads/network/local/
streetworks/cop/safetyatstreetworksandroadworks
[51] DEPARTMENT FOR TRANSPORT. New Roads and Street Works Act 1991: Code of Practice for the
Co-ordination of Street Works and Works for Road Purposes and Related Matters 3rd Edition
2007. Available for download at http://www.dft.gov.uk/pgr/roads/network/local/streetworks/cop/
pdfcoordstreetworksv5
[52] DEPARTMENT FOR TRANSPORT. Code of Practice on Recording of Underground Apparatus in Streets
2002. Available for download at http://www.dft.gov.uk/pgr/roads/network/local/streetworks/cop/
recordingofundergroundappara3888
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BS EN
752:2008
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