CIRIA C714 London, 2014

Transport infrastructure drainage: condition appraisal

and remedial treatmentTim Spink, Ian Duncan, Andrew Lawrance, Mott MacDonald

Andrew Todd, Atkins

Griffin Court, 15 Long Lane, London, EC1A 9PNTel: 020 7549 3300 Fax: 020 7549 3349Email: enquiries@ciria.org Website: www.ciria.org

CIRIA, C714ii

Transport infrastructure drainage: condition appraisal and remedial treatment

Spink, T, Duncan, I, Todd, A, Lawrance, A

CIRIA

C714 RP941 © CIRIA 2014 ISBN: 978-0-86017-717-3

British Library Cataloguing in Publication Data

A catalogue record is available for this book from the British Library

Keywords

Infrastructure asset management, construction process, environmental management, ground engineering, inland waters and groundwater, performance measures, risk and value management, surface water drainage and flooding, sustainability

Reader interest

Condition appraisal and remedial treatment of transport drainage works, including highways and railway infrastructure

Classification

Availability UnrestrictedContent Advice/guidance, basic data, case study,

recommendationsStatus Committee-guided, established knowledgeUser Asset managers, technical managers, engineers,

consultants, contractors

Published by CIRIA, Griffin Court, 15 Long Lane, EC1A 9PN, UK

This publication is designed to provide accurate and authoritative information on the subject matter covered. It is sold and/or distributed with the understanding that neither the authors nor the publisher is thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied, and the authors and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use.

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature.

If you would like to reproduce any of the figures, text or technical information from this or any other CIRIA publication for use in other documents or publications, please contact the Publishing Department for more details on copyright terms and charges at: publishing@ciria.org Tel: 020 7549 3300.

Transport infrastructure drainage iii

Summary

After a long period of neglect, it is increasingly recognised that an effective drainage asset can significantly enhance the performance and life of other major assets such as the pavement, permanent-way and earthworks. Consequently, infrastructure asset owners are demanding improved means and methods to manage their drainage systems so that often limited funds can be directed to the right place, at the right time, giving the optimum result, for all affected assets.

By way of illustration, one of the most significant cross asset impacts is the interaction of drainage with earthworks. The UK Highways Agency estimates that 70 per cent of earthworks failures are due directly or indirectly to deficiencies in the drainage system. Similarly, London Underground considers that drainage-related issues are responsible for the vast majority of significant earthwork failures over the last 20 years.

Recommendations for good practiceThis publication provides guidelines on good practice for the condition appraisal, maintenance and remedial treatment of transport infrastructure drainage, as well as advice on issues such as inspection, investigation and monitoring, asset management, health and safety and environmental issues. It also considers interaction with third party assets, and how transport drainage assets sit in the wider catchment. It includes references to appropriate standards and design guidance for renewals and remedial works. A summary of good practice guidance is provided at the end of each chapter for the key topics covered.

The document is aimed at drainage infrastructure owners and asset managers, organisations or individuals responsible for the routine maintenance and care of drainage assets, and organisations or individuals who are responsible for assessment and remediation of drainage assets.

In summary, this document aims to:

�� present current UK good practice (as of 2013) on transport infrastructure drainage

�� provide a guide for routine management of drainage assets

�� recommend current good practice on condition appraisal and remedial treatment strategies to give best value for money

�� raise knowledge and awareness of the connection between drainage asset performance and other key assets (such as the road pavement, track and geotechnical assets)

�� distil conclusions from existing UK and international research, and practical experience on the whole life management of drainage assets

�� provide example case studies of good practice.

This publication is not a drainage design guide for new drainage works. Balkham et al (2010) should be consulted for its coverage of how maintenance and remediation works should be ‘designed’.

Following a significant cutting failure in 1954, Dr H Golder commented “all engineers dealing with banks knew the important rule was drainage and more drainage”.

CIRIA, C714iv

Acknowledgements

This guide was produced as part of CIRIA’s continuing work in developing a suite of documents for both infrastructure asset management and flood risk management. The project was carried out under contract to CIRIA by a consortium led by Mott MacDonald, with Atkins, Balfour Beatty Civil Engineering Ltd, Carnell Group, and SEAMS Ltd.

Authors

Tim Spink BSc ARSM MSc DIC FGS CGeol

Tim is a technical director at Mott MacDonald with 40 years’ experience in geotechnics, having specialised in drainage and earthworks asset management for the last 15 years. He is the author of national standards and policy documents in drainage and earthworks asset management for both the Highways Agency and Network Rail.

Ian Duncan BEng MSc CGeol CEng MICE MIAM

Ian is a project director at Mott MacDonald with over 20 years’ experience in engineering geology and geotechnical engineering. Since 2001 Ian’s main focus has been earthworks infrastructure asset management for the Highways Agency and more recently, earthworks and drainage related asset management for Network Rail. Ian is a member of the Institute of Asset Management and within Mott MacDonald he has a key co-ordination role for asset management related work across the diverse transportation sector.

Andrew Todd BSc CEng MICE MCIWEM

Andrew is a principal engineer at Atkins with over 35 years’ experience in the design and construction of sewerage and drainage schemes including 20 years research into highway drainage systems. Andrew is the author of drainage asset management and inspection specifications and design guides for the Highways Agency.

Andrew Lawrance BSc (Hons) MSc MRSC CChem CSci SiLC

Andrew is an environmental practice leader for Mott MacDonald, co-ordinating environmental projects throughout the country. He has almost 20 years’ experience with Mott MacDonald, providing advice on environmental and planning aspects of varied projects, including Environmental Impact Assessment, major infrastructure development, due diligence reporting and environmental licensing/permitting applications.

Project steering groupFollowing CIRIA’s usual practice, the research project was guided by a project steering group, which included:

Linda Aucott Defra

Andy Bailey (chair) Highways Agency (formerly Department for Transport)

Richard Dawson Derbyshire County Council

John Dora John Dora Consulting Ltd (formerly Network Rail)

Martin Follows Derby City Council

Transport infrastructure drainage v

Tony Greenstock Arup

Richard Leigh Lanes Group Plc

David Martin Thames Water

John McRobert Northern Ireland Roads Service

Richard Morgan Welsh Assembly Government

Martin Osborne Mouchel

Kamal Panchal Improvement and Development Agency (iDEA)

Peter Ritchie Transport Scotland

Will Rogers URS

Santi Santhalingam Highways Agency

Rajan Sharma Transport for London

Fiona Thomson London Underground

Gareth Toft Gloucestershire County Council

Jim Walker Environment Agency

Project fundersDepartment for Transport/Improvement and Development Agency (iDEA)

Highways Agency

Institution of Civil Engineers Research Enabling Fund

London Underground

Network Rail

Northern Ireland Roads Service

Transport Scotland

CIRIA would also like to thank members of the Geotechnical Asset Owners Forum for inspiring the project and the research consortium for their substantial in-kind contribution in the production and dissemination of this publication.

CIRIA project managersChris Chiverrell Project director

Ben Kidd Project manager

Other contributorsThe development of this guide also used contributions from:

Scott Arthur Heriot-Watt University

Ian Bone Amey

Alison Brown Institution of Civil Engineers

Derek Butcher Network Rail

Andrew Crawshaw London Underground

Chris Digman MWH

Paul Ebbutt London Underground

Jon Elder Tube Lines Ltd

Sue Garlick Network Rail

Stephanie Glendinning Newcastle University

Keith Halstead Mott MacDonald

Owen Jenkins CIRIA

Neil Jones Atkins

CIRIA, C714vi

Steve Jones Balfour Beatty Civil Engineering

Lee Kelly CIRIA

Russell Kimber Network Rail

Stuart Leask Transport Scotland

Brian McGinnity London Underground

Jerry McKay Carnell Group

Adam Noakes Mott MacDonald

Martin Parry Carnell Group

John Perry Mott MacDonald

Andy Phillips (retired) Welsh Assembly Government

Joe Roebuck SEAMS

Gordon Rowlands Carnell Group

Nadar Saffari London Underground

Paul Shaffer CIRIA

Robert Sharpe Tube Lines Ltd

David Sisson Association of Drainage Authorities

Steve Slater Network Rail

Andrew Stevenson East Hertfordshire District Council

John Wotherspoon Atkins

Nick Wallerstein University of Nottingham

Michael Whitehead Highways Agency

Tom Wilson Carnell Group

Transport infrastructure drainage vii

Contents

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.1 What is transport infrastructure drainage?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.1 Railway drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Highway drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.1.3 Drainage hazards for railway and highway operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2 Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101.3 Audience. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101.4 Describing the drainage asset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111.5 What makes drainage different? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

1.5.1 Legacy of a ‘forgotten’ asset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.5.2 Impact of flooding on transport operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131.5.3 Impact of drainage on other assets and adjacent property . . . . . . . . . . . . . . . . . . . . . . . .141.5.4 Impact of other assets on drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151.5.5 Infrastructure resilience. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

2 Asset management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.1 Why manage your assets? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.2 Asset management hierarchy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172.3 Drainage asset management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

2.3.1 Asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202.3.1.1 Inventory data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202.3.1.2 Condition appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

2.3.2 Asset performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.3.2.1 Performance requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212.3.2.2 Performance gaps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

2.3.3 Intervention criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.3.4 Maintenance and remediation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

2.3.4.1 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.3.4.2 Refurbishment and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

2.3.5 Monitoring and feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .232.3.6 Asset Management Plans (AMP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

2.4 Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .242.4.1 Water including flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

2.4.1.1 Flood and Water Management Act 2010 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252.4.2 Health and safety legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.4.3 Duties of riparian ownership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262.4.4 Legislation related to infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

2.4.4.1 Highways Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272.4.4.2 Railway Clauses Consolidation Act 1845 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272.4.4.3 Railways Act 2005. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

2.4.5 Environmental legislation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272.4.6 SuDS legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282.4.7 Waste legislation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292.4.8 Conflict of Acts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

CIRIA, C714viii

2.5 Organisational approaches to drainage asset management . . . . . . . . . . . . . . . . . . . . . . . . . . . . .312.5.1 Highways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

2.5.1.1 Highways Agency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322.5.1.2 Highway authorities, Transport for London, Welsh Government and Transport Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

2.5.2 Railways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352.5.2.1 Network Rail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352.5.2.2 London Underground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

2.5.3 Water companies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372.5.4 Canal & River Trust (England and Wales) and Scottish Canals. . . . . . . . . . . . . . . . . . . . . .37

2.6 Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372.7 Asset owner collaboration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

3 Loss of performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .403.2 How the asset degrades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .403.3 Consequences of degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .423.4 Service degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

3.4.1 Sediment deposition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .433.4.2 Vegetation and root growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443.4.3 Calcite deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .463.4.4 Debris accumulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

3.5 Structural degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .473.5.1 Material deterioration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

3.5.1.1 Erosion of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.1.2 Brick construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48

3.5.2 Piped systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.2.1 Flexible pipes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483.5.2.2 Problematic pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

3.6 Cross asset impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503.7 Third party impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

3.7.1 Third party damage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .513.7.2 Change of catchment areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .523.7.3 Illegal connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52

3.8 Influence of maintenance regime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533.8.1 Consequences of poor maintenance regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

3.9 Review of current design principles in relation to designing for maintenance . . . . . . . . . . . . . . .563.9.1 Preventing sediment deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

3.9.1.1 Flow velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563.9.2 Estimating sediment volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .583.9.3 Effects of structural loading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .583.9.4 Depth of piped drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

4 Condition appraisal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

4.1 Drainage condition vs performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .604.2 Asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

4.2.1 Types of asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .614.2.2 Sources of asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64

4.2.2.1 Historical drainage records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .654.2.2.2 Inspections and surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .654.2.2.3 Indirect data sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .664.2.2.4 Incident reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .664.2.2.5 Parent asset surveys and inspections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .674.2.2.6 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67

4.2.3 Type of data required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .684.2.4 Level of inventory data required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Transport infrastructure drainage ix

4.2.5 Level of condition data required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .704.3 Phased approach to knowledge acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70

4.3.1 Costs of knowledge acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .704.3.2 A staged approach to drainage asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

4.4 Inspections and surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .724.4.1 UK infrastructure standards and guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .724.4.2 Current, new and innovative drainage survey technologies and procedures . . . . . . . . . . 74

4.4.2.1 Survey tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .754.4.2.2 Field procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .754.4.2.3 Office procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .754.4.2.4 Data formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

4.4.3 Special considerations and constraints for the infrastructure working environment. . . .764.4.4 Review of procedures for targeted and representative surveys . . . . . . . . . . . . . . . . . . . . .774.4.5 Cross asset survey co-ordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

4.5 Condition assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .784.5.1 Asset level condition grading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .784.5.2 Detailed defect level condition scoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .804.5.3 Determination of performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .814.5.4 Condition as a proxy for performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82

4.6 Data management databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .824.6.1 Managing drainage data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .824.6.2 Review of current drainage asset management databases . . . . . . . . . . . . . . . . . . . . . . . .844.6.3 Asset data visualisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .854.6.4 Asset data analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .884.6.5 Asset knowledge performance indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .894.6.6 Asset management performance indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .894.6.7 Drivers for common standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90

5 Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .925.1.1 Background and motivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .925.1.2 Environmental legislation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92

5.2 Application of sustainable drainage systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .935.2.1 SuDS relevant to transport infrastructure drainage systems . . . . . . . . . . . . . . . . . . . . . . .935.2.2 Retrofitting SuDS to existing transport infrastructure drainage systems . . . . . . . . . . . . .945.2.3 Financial mechanisms for SuDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

5.3 Wastewater and solid waste disposal, water quality and control of contaminants. . . . . . . . . . . .955.3.1 Review of procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95

5.3.1.1 Wastewater management and treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .955.3.1.2 Solid waste management and disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .965.3.1.3 Discharge consents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

5.3.2 Current and emerging practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .975.4 Carbon footprint considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

5.4.1 Assessment procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .985.5 Use, reuse and conservation of natural resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

5.5.1 Review of current reuse and recycling practice relevant to infrastructure drainage . . . .985.5.2 Current and emerging practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

5.6 Other environmental issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .995.6.1 Flood risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99

5.6.1.1 Design standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.6.2 Pollution assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005.6.3 Biodiversity and vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1015.6.4 Noise and vibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1015.6.5 INSPIRE Directive 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

6 Decision making process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

CIRIA, C714x

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1036.2 Strategic policy options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

6.2.1 Sustainable investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.3 Risk assessment approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

6.3.1 Definition of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1076.3.2 Hazard identification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1086.3.3 Likelihood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1086.3.4 Consequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1086.3.5 Criticality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096.3.6 Tolerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

6.4 Strategic risk-based policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1106.5 Development of unconstrained work schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1126.6 Development of constrained work schedule. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

6.6.1 Prioritising the works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1136.6.2 Intervention options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1136.6.3 Costing the works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

6.7 Major works items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1156.8 Decision support tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

6.8.1 Whole life cost analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1166.8.2 Balancing maintenance vs. repair and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1176.8.3 Available decision support tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1176.8.4 Deterioration modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

6.8.4.1 Performance deterioration modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196.8.4.2 Condition deterioration modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

7 Maintenance, refurbishment and renewal techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1227.2 Some typical problems and remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.3 Piped drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

7.3.1 Maintenance of piped drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1297.3.1.1 Rodding (and dragging/winching) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1297.3.1.2 High pressure jetting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1297.3.1.3 Low pressure – high volume flushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307.3.1.4 Root cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307.3.1.5 Grinders/encrustation removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

7.3.2 Refurbishment and renewal of piped drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307.3.2.1 Patch lining repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307.3.2.2 Slip-lining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1317.3.2.3 Cured-in-place pipe (CIPP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1317.3.2.4 Pipe reaming/bursting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1337.3.2.5 Open cut repairs vs. trenchless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

7.4 Non-piped drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347.4.1 Maintenance of non-piped drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

7.4.1.1 Drainage ditch re-profiling and cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347.4.1.2 Cyclical gully cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347.4.1.3 Vegetation control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.1.4 Channel sweeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

7.4.2 Refurbishment and renewal of non-piped drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.2.1 Chamber repointing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.2.2 Chamber grout or resin injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.2.3 Other methods for chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.2.4 Filter drain refurbishment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1357.4.2.5 Filter drain stabilisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1377.4.2.6 Pond refurbishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137

7.5 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1377.5.1 General pipework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137

Transport infrastructure drainage xi

7.5.2 Flexible pipe installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1387.5.3 Non-pipework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

8 Future research and new technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Statutes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149

Useful websites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

A1 Case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

A2 Drainage standards and guidance documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

A3 Inspection and survey methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Boxes

Box 1.1 Influence of drainage condition on earthwork stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Box 1.2 Highway drainage problems, Hertfordshire County Council. . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Box 1.3 Derailment near Gillingham tunnel, Dorset 28 November 2009. . . . . . . . . . . . . . . . . . . . . . .15Box 2.1 Asset management planning activities – definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Box 2.2 Priority assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Box 2.3 Severe flooding, Gloucestershire, 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Box 2.4 Highways asset management – successful Element 2 submissions 2011 . . . . . . . . . . . . . .34Box 2.5 Third party flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Box 2.6 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Box 3.1 A41 Gloucester collapsed pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Box 3.2 The impact of wet-beds on the rail environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Box 3.3 The adverse effect of poor drainage on track quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Box 3.4 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59Box 4.1 Pumped system remote monitoring – focused on SCADA . . . . . . . . . . . . . . . . . . . . . . . . . . . .67Box 4.2 Remote monitoring trial by Lanarkshire Council and SEPA . . . . . . . . . . . . . . . . . . . . . . . . . . .68Box 4.3 M45 drainage surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Box 4.4 Use of the Condition Assessment Manual (Environment Agency, 2006a) ratings for

drainage by East Herts District Council . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Box 4.5 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Box 5.1 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102Box 6.1 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121Box 7.1 Maintaining aged drainage assets: the London Underground experience . . . . . . . . . . . . . 125Box 7.2 Managing drainage assets in the built environment – the TfL experience. . . . . . . . . . . . . 126Box 7.3 London Underground cyclical cleaning and inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Box 7.4 Pipe lining repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Box 7.5 Fire damage to drainage assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Box 7.6 The advantages and suitability of trenchless techniques (from a rail perspective). . . . . . 134Box 7.7 Filter drain refurbishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Box 7.8 Lightweight catchpits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139Box 7.9 Good practice guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Case studies

Case study A1.1 Developing a risk-based drainage strategy: Network Rail’s Railway Drainage Systems Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Case study A1.2 Daventry drainage failure thought to be due to third party runoff. . . . . . . . . . . . . . . . . . . . 156Case study A1.3 Highways Agency Drainage Data Management System (HA DDMS) . . . . . . . . . . . . . . . . . . .157Case study A1.4 Local authority good practice, drainage asset mapping, Gloucestershire . . . . . . . . . . . . . 159Case study A1.5 Highways asset management – successful Element 2 submissions, 2011 . . . . . . . . . . . .161Case study A1.6 Risk factor study from inclement weather impact on earth structures . . . . . . . . . . . . . . . 163Case study A1.7 Developing a drainage whole life cost model for the Highways Agency . . . . . . . . . . . . . . . .166Case study A1.8 Tramway drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169

CIRIA, C714xii

Figures

Figure 1.1 Typical piped cess collector drain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Figure 1.2 Typical piped drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Figure 1.3 Track drainage – ballast and catchpit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Figure 1.4 Typical off-track drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Figure 1.5 An example of embankment drainage for a road system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Figure 1.6 An example of cutting drainage for a road system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Figure 1.7 Highway drainage – channel and gully system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Figure 1.8 Highway drainage – toe ditch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Figure 1.9 Highway flooding – runoff from adjacent farmland. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Figure 1.10 Shallow brickwork pipe – collapse resulted from heavy repeated dynamic loading . . . . . . . . 6Figure 1.11 Wet-beds resulting from ineffective track drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Figure 1.12 View of cutting C066/CTS2 looking north on 10 February 2003 . . . . . . . . . . . . . . . . . . . . . . . 8Figure 1.13 View of large tree (later removed) on cutting C066/CTS2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Figure 1.14 Pavement deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 1.15 Patch repair failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 1.16 Unmaintained toe ditch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 1.17 Asset interactions and consequences of failure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Figure 2.1 Asset management hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Figure 2.2 Overview of asset management process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Figure 2.3 Sewerage risk management model for developing management plans . . . . . . . . . . . . . . . . .24Figure 2.4 An outfall on the M1 where the penstock was added as a pollution control device following

an assessment of the pollution risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30Figure 2.5 Schematic illustration of drainage policy priorities by infrastructure owner . . . . . . . . . . . . .32Figure 2.6 Defective highway drainage causing standing water on the A417 . . . . . . . . . . . . . . . . . . . . .34Figure 2.7 Construction of new weir within the River Isbourne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Figure 2.8 Culvert clearance requiring dewatering of the river: methods to protect spawning fish

and native crayfish were agreed with the Environment Agency and carried out on site . . . .34Figure 2.9 Soakaway with M1 in the background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Figure 2.10 Houses that were flooded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Figure 2.11 Soakaway with houses in the background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Figure 2.12 Soakaway being remediated in 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Figure 3.1 Rates of asset deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Figure 3.2 Sediment accumulated in a catchpit. Note the misalignment of the step irons . . . . . . . . . .44Figure 3.3 Coarse sediment and litter debris blocking bridge deck drain . . . . . . . . . . . . . . . . . . . . . . . .44Figure 3.4 Sediment and debris filling the gully pot sump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Figure 3.5 Blocked inlet headwall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Figure 3.6 Tree roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45Figure 3.7 Invasive vegetation in ponds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45Figure 3.8 Invasive vegetation in ditches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45Figure 3.9 Lack of established vegetation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46Figure 3.10 Examples of debris accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47Figure 3.11 Collapsed flexible pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Figure 3.12 Gas mains installation through drainage pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Figure 3.13 Repair to pipe damage caused by excavation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Figure 3.14 Sheet pile from platform works damaging a drainage pipe . . . . . . . . . . . . . . . . . . . . . . . . . . .51Figure 3.15 Signal cable running along a drainage pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Figure 3.16 Third party misuse of a road culvert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Figure 3.17 Standing water above drainage pipe in trial trench . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Figure 3.18 Slurry pumped into ballast in the cess. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Figure 3.19 A catchpit blocked with silt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Figure 3.20 A catchpit with still water above the invert level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Figure 3.21 Catchpits filled with slurry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Figure 3.22 Poor channel outlet maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Transport infrastructure drainage xiii

Figure 3.23 Blocked culvert screen as a result of lack of maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . .56Figure 4.1 Drainage asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62Figure 4.2 Progress towards drainage asset knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63Figure 4.3 Flow stage data, imaging and retrieval web page (a), and associated camera image

display web page (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68Figure 4.4 GIS overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83Figure 4.5 Base mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85Figure 4.6 Visual index to scanned as-built drawings and records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Figure 4.7 Geo-referenced scanned as-built drawings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Figure 4.8 Digital drainage inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Figure 4.9 Asset level condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Figure 4.10 Defect level condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 4.11 Schematic defect level condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 4.12 Consequential problems resulting from drainage failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Figure 4.13 Assets at risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88Figure 4.14 Flow modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88Figure 6.1 The decision making process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104Figure 6.2 Drainage policies: performance–age curves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Figure 6.3 Drainage policies: annual cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Figure 6.4 Drainage policies: cumulative (whole life) cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106Figure 6.5 Criticality of location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Figure 6.6 Relationship between pipe blockage rate and pipe material and diameter . . . . . . . . . . . . 120Figure 6.7 Relationship between pipe age and probability of failure for vitreous clay pipes . . . . . . . 120Figure 6.8 Structural and service condition deterioration curves for Highways Agency gullies . . . . . .121Figure 7.1 Resin impregnation of cured-in-place pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131Figure 7.2 Close up of liner and steam injection head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Figure 7.3 Works carried out with no disruption to the traffic flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132Figure 7.4 Remains of the burnt combined kerb and drain system . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Figure 7.5 Damage to plastic pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133Figure 7.6 In situ recycling of the M4 central reservation filter media . . . . . . . . . . . . . . . . . . . . . . . . . 136Figure 7.7 The filter drain was ineffective before refurbishment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Figure 7.8 The newly refurbished filter drain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Figure 7.9 Example of catchpits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139Figure A1.1 Eroded ditch adjacent to the A5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154Figure A1.2 Landslip caused by exceedance of drainage capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155Figure A1.3 Scanned and geo-referenced as-built drainage drawing overlaid on aerial photography. . 156Figure A1.4 Spill model showing predicted flow path, pollution control device and outfall. . . . . . . . . . .157Figure A1.5 Mapped drainage coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158Figure A1.6 Close-up of street level drainage records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Figure A1.7 Close-up of street level drainage records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Figure A1.8 Sonde tracking drainage pipe locations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160Figure A1.9 Factors influencing the likelihood of flow failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Figure A1.10 Cutting M034 CTS11 crest drain (a) and gabion toe wall (b) . . . . . . . . . . . . . . . . . . . . . . . . 164Figure A1.11 Cutting M032 CTS17 gully (a) and catchpit (b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165Figure A1.12 Water industry derived relationship between pipe diameter (mm) and blockage rate for

concrete (CO), vitreous clay (VC) and plastic (PL) pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167Figure A1.13 Example WLC model output showing how a pro-active investment policy would improve

asset condition and reduce flooding over a number of years . . . . . . . . . . . . . . . . . . . . . . . .167Figure A1.14 Shudehill tram stop in Manchester, showing distressed tracks and surfacing . . . . . . . . . .169

Tables

Table 1.1 Document map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Table 1.2 High level grouping of drainage asset types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Table 1.3 Glossaries of drainage terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Table 2.1 Estimated quantities of drainage assets by major UK infrastructure owner . . . . . . . . . . . . .20

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Table 2.2 UK infrastructure asset owners’ estimates of drainage knowledge (%) . . . . . . . . . . . . . . . . .21Table 2.3 Key legislation for implementation of SuDS in the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Table 3.1 Modes of deterioration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41Table 3.2 Problematic pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Table 3.3 Problems arising from a poor drainage maintenance regime . . . . . . . . . . . . . . . . . . . . . . . . .54Table 3.4 Pipe diameters and gradients. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Table 3.5 Summary of design parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Table 4.1 Drainage condition vs. performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61Table 4.2 Sources of drainage data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Table 4.3 Generic drainage survey and inspection types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66Table 4.4 Types of drainage data required for various asset management tasks . . . . . . . . . . . . . . . . .69Table 4.5 Survey and inspection frequencies in UK infrastructure owners’ specifications and

standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73Table 4.6 Approaches to condition assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Table 4.7 Comparison of asset level grading systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Table 4.8 WRc sewer pipe structural condition grade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81Table 4.9 WRc sewer pipe service condition grade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81Table 4.10 Condition as a proxy for performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82Table 4.11 Summary of some of the current UK drainage asset management systems . . . . . . . . . . . . .85Table 5.1 SuDS relevant to transport infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93Table 5.2 Pollutant sources from transport, which may be encountered in transport drainage

infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95Table 5.3 Flood risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99Table 6.1 Risk assessment definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107Table 6.2 Example application of policy options by route criticality. . . . . . . . . . . . . . . . . . . . . . . . . . . .110Table 6.3 Example cross asset interaction risk matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110Table 6.4 Example reactive cross asset policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111Table 6.5 Example optimum proactive cross asset policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111Table 6.6 Example intervention decision matrix for point assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114Table 6.7 Example intervention decision matrix for linear assets . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114Table 6.8 Whole life costs for infrastructure drainage systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .116Table 6.9 Summary of DST model types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117Table 6.10 Summary of DST methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118Table 7.1 Description of intervention options, relative costs and their impact on asset condition . . . 123Table 7.2 Intervention options, application and industry use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124Table 7.3 Application of intervention types to frequently observed drainage problems . . . . . . . . . . .127Table A1.1 Pipework asset inventory extrapolation rules dependent on asset age. Figures are km

of pipework per km of road . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166Table A1.2 Non-pipework asset inventory estimation rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166Table A3.1 Summary of drainage inspection equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .172Table A3.2 Summary of drainage survey location equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176Table A3.3 Summary of drainage survey recording equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177Table A3.4 Summary of drainage survey software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177Table A3.5 Summary of drainage data formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178

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Glossary

Appraisal The qualitative process of understanding the state of an existing asset or asset system to inform the planning of future interventions.

Assessment The quantitative process of understanding the performance or structural competence of an existing asset or asset system to inform the planning of future interventions.

Asset management Systematic and co-ordinated activities through which an organisation optimally and sustainably manages its assets and asset system. This includes their associated performance, risks and expenditures over their life cycles for the purpose of achieving its strategic aims.

Ballast The coarse granular layer that supports the track.

Blanket A structural layer that, with the ballast, forms part of the track support system.

Carrier drain A closed drainage pipe that transports water from an inlet to an outlet without the addition of further volume.

Catchment The area of land that drains to a given point on a river, drainage system or other body of water.

Catchpit A chamber located at regular intervals along a piped drainage system. The catchpit has a sump that allows collection of sediment and foreign objects, which have entered the drainage system and also allows access to the pipework for survey and maintenance works.

Cess The area to the side of the rail and ballast shoulder.

Collector drain An open drainage system that collects water along the length of the system and transports it to an outlet.

Condition appraisal The range of activities involved with the qualitative evaluation of an asset’s condition and performance (ie the gathering of existing data, inspection, investigation and structural assessment).

Condition assessment A measure or measures of the asset carried out as a precursor to the performance assessment, for example, measurements of service and structural condition of the asset.

Controlled waters All watercourses, lakes, lochs, coastal waters and water contained in underground strata as defined and protected by the Water Resources Act 1991.

Counterfort A deep stone-filled trench installed to both strengthen an earthwork and improve drainage.

Crest drain A drain at the top of a slope that intercepts and directs flow from an adjacent catchment.

Culvert A closed conduit carrying a watercourse beneath an obstruction such as a road, railway or canal. The term ‘closed’ implies that a culvert has a hard soffit and invert. The term ‘conduit’ implies the conveyance of water some or all of the time, but excluding tunnels and underpasses for vehicles, pedestrians and animals.

Debris Solid materials transported in a watercourse, including natural and man-made, buoyant and non-buoyant materials, but excluding sediment. See also Trash.

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Design life The service life of an asset intended by the designer. This assumes some rate of deterioration up to a point where the asset requires replacement or refurbishment.

Discharge Also known as flow rate or abbreviated to flow. The volume of water passing a given point of an open channel or closed conduit in unit time, normally expressed in cubic metres per second (m³/s).

Earthwork A cutting or embankment formed through the natural terrain to permit manageable gradients for transport corridors.

Environmental impact Detailed studies that predict the effects of a development project on the assessment (EIA) environment and provide plans for mitigation of the adverse effect.

Erosion Removal of particles from the substrate by wind, flowing water or wave action.

Antonym = accretion.

Failure Inability to achieve a defined performance threshold. ‘Catastrophic failure’ describes the situation where the consequences are immediate and severe.

Flap gate/valve A gate designed to close when the downstream water level exceeds the upstream water level. Frequently used for drainage outfalls into tidal waters and rivers to prevent backflow.

Flow rate The volume of water passing a given point in unit time, normally expressed in cubic metres per second (m³/s). See also Discharge.

Fly-tipping Illegal disposal of waste on land that has no licence to accept waste

Full flow Flow in a closed conduit in which the water surface just reaches soffit level, but does not flow under pressure.

Geotextile Permeable synthetic or natural fibre fabric used to provide erosion protection, filtration, separation, drainage or soil reinforcement.

Greywater Wastewater from showers, baths, and wash basins.

Hazard An event or condition that has the potential to occur and affect performance. A hazard does not necessarily lead to harm and it can be managed.

Head The total energy per unit weight of fluid expressed in metres of water above a datum.

Headwall The retaining wall at a culvert or pipe inlet or outlet that provides support to the embankment.

Invert The lowest internal point of any cross-section in a culvert or pipe.

Level of service “The defined service quality for a particular activity against which service performance may be measured. Service levels usually relate to quality, quantity, reliability, responsiveness, environmental acceptability and cost” (INGENIUM, 2006). “The description of the service output for a particular activity or service area against which performance may be measured.” (Roberts and Hollier, 2007).

Main river A watercourse in England or Wales is shown as a ‘main river’ on a map prepared by the Environment Agency under the Water Resources Act 1991. The main river designation includes the watercourse, its banks and any connected drainage works. In England and Wales, the Environment Agency has permissive powers to carry out flood defence works on main rivers but responsibility for maintenance remains with the riparian owner. Watercourses not designated as ‘main river’ are known as ordinary watercourses.

Mandrel A tool component that can be used to grip other moving tool components.

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Ordinary watercourse All watercourses not designated as main river. Permissive powers to carry out flood defence works on an ordinary watercourse lie with the local authority or internal drainage board but responsibility for maintenance remains with the riparian owner.

Pathway Route that enables a hazard to propagate from a ‘source’ to a ‘receptor’, as in the source-pathway-receptor concept. A pathway must exist for a hazard to be realised. Pathways can be constrained to mitigate the risks.

Performance assessment A comparison of present performance against performance requirements. The assessment considers the effect of condition on each performance requirement and the effect of each performance requirement on the performance of the subsystem or system. The key to performance assessment is an understanding of the link between asset (or system) condition and its response under a range of loading conditions. Outputs from this stage are the probability of failure and residual life.

Performance indicator Also known as performance measure. Specific, measurable and time-related output of a particular asset management policy or project. May be technical such as average asset condition, or more generic such as public satisfaction.

Performance requirement The hydraulic, structural, environmental or other standards that an asset or system is built and maintained to.

Probability Measure of the chance that an event will occur. Typically defined as the relative frequency of occurrence of that event out of all possible events and expressed as a percentage with reference to a time period, eg one per cent annual exceedance probability.

Receptor The entity, such as a person, property or habitat, which may be harmed by an event via a source and pathway. The vulnerability of a receptor can be reduced by increasing its resilience.

Re-grading Re-profiling the bed of a channel or ditch to a lower level or more even gradient (for example, to increase flow capacity or improve land drainage).

Resilience In asset management, the ability of an asset or asset system to resist the damaging effect of extreme loading. Resilience measures can, for example, help to achieve design standards beyond the standard of protection.

Return period The average length of time between flood events of a similar magnitude, eg a 100-year flood occurring on average once every 100 years. Annual exceedance probability (AEP) is the preferred term for flood risk management, one per cent AEP being equivalent to a 100 year return period.

Revetment Works to protect the bed or banks of a channel against erosion, typically constructed from stone or concrete blocks.

Riparian Along the banks of a watercourse. Riparian zones support riparian vegetation and are of environmental importance, providing diverse habitats and supporting a range of ecological communities.

Riparian owner Owner of land adjoining a watercourse.

Risk Risk can be considered as having two components:

1 The probability that an event will occur.

2 The consequence associated with that event to receptors.

Risk is a function of probability and consequence.

Risk assessment The process of identifying hazards and potential consequences, estimating the magnitude and probability of consequences, and assessing the significance of the risk(s). A ‘tiered’ approach can be used with the effort in

CIRIA, C714xviii

assessing each risk proportionate to its importance in relation to other risks and likely consequences.

Risk management The systematic process of risk assessment, options appraisal and implementation of any risk management measures to control or mitigate risk.

Runoff Overland flow produced by rainfall.

Scour Erosion of the bed or banks of a watercourse by the action of moving water, typically associated with channel constriction by a local feature such as a bridge pier.

Sediment Granular or cohesive material such as clay, sand, gravel, cobbles or boulders, which is transported in flowing water and settles or tends to settle in areas where the flow slows down.

Sedimentation The deposition of sediment in a drainage system.

Service condition Relates to the water carrying capacity of a drainage asset and the severity of the defects that reduce its capacity below its original design level, but is independent of the structural condition. Service defects are addressed by maintenance of the asset such as cleaning or vegetation clearance.

Service life The period of time after construction or refurbishment when an asset meets or exceeds its functional performance requirements.

Site investigation The historic and geologic examination of a potential development site to design the foundations of surface buildings, roads etc. It includes geophysical surveys, trial pits, and boreholes.

Soffit The highest internal point of any cross-section in a culvert or pipe.

Source-pathway-receptor How a hazard propagates from its source, via a pathway to a receptor. For example, in the event of heavy rainfall (the source) floodwater may escape from a river and propagate across the floodplain (both elements of the pathway) to inundate a housing development (the receptor), which may suffer material damage.

Special waste Special waste describes any waste with hazardous properties, which may render it harmful to human health or the environment.

Structural condition Relates to the fabric of a drainage asset and the severity of the physical defects that affect its integrity. Structural defects are addressed by repairing or replacing the asset.

Sustainability The concept of development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

Swale A wide shallow grassed channel to carry storm runoff to a discharge point, provide flow attenuation and allow infiltration to groundwater.

Tamping Compaction of the ballast to correct track geometry defects.

Trash Any buoyant or semi-buoyant material carried by the flow of water in a channel that could accumulate inside a culvert or pipe to form a blockage, and will accumulate on a screen. See also Debris.

Trash screen Screen at the inlet of a culvert or pipe designed to prevent debris from entering and causing blockage.

Waste management licence This is an environmental licence granted for specific activities.

Waste acceptance criteria A process to determine if a waste material is suitable for landfill.

Watercourse All rivers, streams, burns, ditches, drains, cuts, culverts, dykes, sluices, sewers and passages carrying or designed to carry water (whether for the

Transport infrastructure drainage xix

time being carrying water or not), excluding pipes or other works for the sole purpose of supplying water to any premises.

Wet-beds Failure of the track drainage system resulting in softening of the trackbed formation combined with repeated train loading causing fines from the formation to pump up into the track ballast, reducing the load carrying capacity of the ballast and adversely affecting track line and level and ride quality.

Whole life cost Total cost of managing an asset over its life, including cost of construction, use, operation, inspection, maintenance and refurbishment, replacement or disposal.

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Abbreviations and acronyms

AC Alternating current

ACAC Asset condition assessment and certification

ADA Association of Drainage Authorities

AMOR Asset Maintenance and Operational Requirements

ASC Asset support contract

BIM Building information modelling or business information management

BOD Bio-chemical oxygen demand

CAD Computer aided design

CAR Water Environment (Controlled Activities) Regulations

CBA Cost benefit analysis

CCTV Closed circuit television

CIPP Cured-in-place pipe

CIPR Cured-in-place repair

CDM Construction (Design And Management) Regulations 2007

CFMP Catchment Flood Management Plan

CLG Department for Communities and Local Government

CPNI Centre for the Protection of National Infrastructure

cSAC candidate Special Area of Conservation

DAMP Drainage asset management plan

DC Direct current

DECC Department of Energy and Climate Change

Defra Department for Environment, Food and Rural Affairs

DfT Department for Transport

DMRB Design Manual for Roads and Bridges

DPoE Drainage Panel of Experts

DRN Detailed River Network (Environment Agency)

DST Decision support tool

EA Environment Agency

EC European Community

EIA Environmental Impact Assessment

EU European Union

FRA Flood risk assessment

GBR General binding rules

GIS Geographic information systems

GRID Geographical Resource Information Depository

HA Highways Agency

HA DDMS Highways Agency Drainage Data Management System

HAMP Highways Asset Management Plan

HAWRAT Highways Agency Water Risk Assessment Tool

HGV Heavy goods vehicle

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IDB Internal Drainage Board

IGT Innovation and Growth Team

LA Local authority

LCA Life cycle analysis

LCC Life cycle cost

LiDAR LIght Detection And Ranging

LLFA Lead local flood authority

LU London Underground

MCHW Manual of Contract Documents for Highway Works

MEAV Mean equivalent asset value

MTBE Methyl Tertiary Butyl Ether

NIEA Northern Ireland Environment Agency

NMM Network Management Manual

NR Network Rail

NRSWA New Roads and Streetworks Act

NRW Natural Resources Wales

NSWG National SuDS Working Group

OFWAT Office of the Water Regulator

ORR Office of the Rail Regulator

OS Ordnance Survey

pSAC possible Special Area of Conservation

pSPA potential Special Protection Area

PAH Polycyclic aromatic hydrocarbons

PAS Publicly Available Specification

PGI Planned general inspection

PPG Pollution Prevention Guidelines

PPS Planning Policy Statement

QA Quality Assurance

RACI Responsibility, accountability, consulted and informed matrix

RAIB Railway Accident Investigation Branch

RDS River Defence Survey

RMMS Routine Maintenance Management System

RWSC Routine and Winter Service Code

SCADA Supervisory Control and Data Acquisition

SEPA Scottish Environment Protection Agency

SMP Sewerage Management Plan

SPA Special Protection Area

SSSI Site of Special Scientific Interest

SuDS Sustainable drainage systems

SWMP Surface Water Management Plan

TAMP Transport Asset Management Plan

TAN Technical Advice Note

TfL Transport for London

TRL Transport Research Laboratory

TSO The Stationery Office

CIRIA, C714xxii

UV Ultraviolet

WG Welsh Government

WIS Water Industry Specification

WFD Water Framework Directive

WLC Whole life cost

WRc Water Research Centre

Transport infrastructure drainage 1

1 Introduction

1.1 WhAT IS TRAnSpoRT InfRASTRuCTuRe DRAInAGe?A drainage system is a series of interlinked components that conducts surface or subsurface water away from sensitive structures such as track, pavement and earthworks. The general purpose of a drainage system is similar for all transport infrastructure, however how this is achieved and the consequent risks to the transport operations are different. The principal drivers for highway drainage systems are flood and pollution prevention, and longevity of the pavement. For railways, the drivers are effective track support and performance, and associated earthworks safety.

The specific issues relating to railway and highway infrastructure are discussed in the following sections.

1.1.1 Railway drainageLondon Underground define the drainage system in terms of ‘track’ (serves the track and is adjacent to it), ‘off-track’ (serves the track but is physically distant from it) and ‘slope drainage’ (serves the earthworks asset). The principal function of track and off-track drainage is to collect and convey water away from the track, trackbed and formation.

Network Rail (2010) states “the purpose of the track drainage is to remove water from the track support system”. It also defines off-track drainage as “a drainage system designed and installed to drain a catchment other than the track support system. The term includes drainage systems outside Network Rail’s property boundary.” Figures 1.1 and 1.2 provide typical diagrams of a track drainage system.

Figure 1.1 Typical piped cess collector drain (courtesy Network Rail)

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Figure 1.2 Typical piped drain (courtesy Network Rail)

The quality of the track in terms of its ability to retain good geometry and its response to mechanical maintenance (such as tamping) is directly related to the design and condition of the track ballast, the underlying earthworks formation and the associated track drainage. These three components interact and where the drainage is inadequate or absent, then either or both of the other components may deteriorate, with a consequential adverse impact on track geometry. The track drainage is the total system that collects rain falling on the track and any groundwater and carries it away. It comprises a permeable trackbed, filtration through to a collector drain with silt deposition in catchpits. Figure 1.3 illustrates track drainage in the form of catchpit and ballast system. The interstices between the ballast form an interconnecting series of drainage paths that are an integral part of the system. Blockage or partial blockage of the ballast interstices can hinder the passage of water to the shoulder or collector and lead to water accumulation in the trackbed and consequential deterioration of the formation and/or ballast (known as wet-beds, see Box 3.2). This interrelationship between the drainage role of the ballast and collector system and the structural role of the ballast and the formation is crucial in achieving satisfactory behaviour of the whole trackbed. Failure to address the track drainage when the trackbed is renewed or maintained can be a serious false economy.

Slope drainage comprise slope face drains (eg cascades, counterforts), crest/toe drains and ditches that collectively contribute to the safety of the earthworks asset by controlling ground and surface water that can cause slope failures. Figure 1.4 illustrates slope drainage in the form of a toe ditch.

Figure 1.3 Track drainage – ballast and catchpit (courtesy Network Rail)

Transport infrastructure drainage 3

Figure 1.4 Typical off-track drainage (courtesy Network Rail)

This guide is focused on where the water enters an engineered drainage pathway within the track or off-track drainage system, eg a collector drain or filter drain. While it is appreciated that track ballast has an important contribution to the drainage of the track, it is not the purpose of this guide to describe the design or maintenance of the track ballast. For guidance on the inspection and assessment of the ballast and blanket, refer to London Underground (2012b and 2012c).

1.1.2 highway drainageFor the highways network, the Highways Agency (HA) considers that there are three major objectives in the drainage of trunk roads (see DMRB, TSO, 2009a):

�� the removal of surface water to provide safety and minimum nuisance

�� provision of effective subsurface drainage to maximise longevity of the pavement and its associated earthworks

�� minimising the impact of the runoff on the receiving environment.

It is also necessary to consider drainage of earthworks and structures associated with the highway. Figures 1.5 and 1.6 provide typical diagrams of a highway drainage system for an embankment and cutting respectively.

Figure 1.5 An example of embankment drainage for a road system (courtesy Mott MacDonald)

CIRIA, C7144

Figure 1.6 An example of cutting drainage for a road system (courtesy Mott MacDonald)

In addition, the DMRB (TSO, 2009b) states that “any water on a road has a lubricating effect and therefore significantly reduces friction between vehicle tyres and the road compared with dry conditions”. So, for the safe operation of the roads the pavement should shed water in an effective manner to a series of receptors and onwards to a location where it does not affect the road user. The drainage of water from the road pavement (or adjacent earthworks) begins at the point that it falls, and it is dispersed as a result of gradient and, on the pavement, through tyre contact. The flow passes across the road surface and through the macrotexture of the road surfacing to a point where the water is collected and enters an ‘engineered’ drainage system as illustrated in Figures 1.7 and 1.8.

Figure 1.7 Highway drainage – channel and gully system (courtesy Mott MacDonald)

Transport infrastructure drainage 5

Figure 1.8 Highway drainage – toe ditch (courtesy Mott MacDonald)

Although the pavement gradient and surface wearing-course, together with the composition of the road formation, clearly contribute to the effective drainage of the road these elements are not considered further. For guidance on the design of pavements (to promote effective drainage), reference may be made to (among others) the DMRB (TSO, 2009a and b).

1.1.3 Drainage hazards for railway and highway operatorsThe ‘immediate’ drainage related hazard that affects the highway is flooding and the creation of a slippery road surface. A flood would potentially cause significant disruption to the road users such as through speed restrictions and/or diversions, or vehicular failure in serious cases. Figure 1.9 shows a typical flood event on a major highway. Pollution control as a result of a spillage is also a key requirement of a highway drainage system.

For rail operators, diversion routes are not readily available and the immediate impact of flooding or pipe/culvert structural collapse (see Figure 1.10), on the safe operation of the railway can be much more significant, resulting in total closure or worse, derailment. High water levels and/or ponding can also cause signalling problems and interfere with the power supply.

CIRIA, C7146

Figure 1.9 Highway flooding – runoff from adjacent farmland (courtesy Mott MacDonald)

Figure 1.10 Shallow brickwork pipe – collapse resulted from heavy repeated dynamic loading (courtesy London Underground)

Transport infrastructure drainage 7

Figure 1.11 Wet-beds resulting from ineffective track drainage (courtesy London Underground)

The long-term hazards result from the impact of drainage exceedance on other assets, and are similar for both transport systems. For example, the (prolonged) presence of water in the earthwork, ballast, sub-base and sub-grade can seriously affect the life of these layers and the infrastructure that it supports, eg the track or pavement wearing course. A poorly maintained drainage system may occasionally flood, but it may continually leak (a pipe) or hold water (ballast/blanket) softening the support to the road/rail. For railways, the permeable nature of the trackbed actively promotes water entry into the earthwork, so capture and effective transport of the water is required to avoid ponding. Figure 1.11 shows the results of long-term softening of the track formation resulting in the formation of ‘wet-beds’ and consequent loss of performance. Further examples of cross asset impacts are given in Section 1.5.3.

The UK rail system and older highway networks are likely to have an increased risk of deformation or failure from inadequate drainage due to their age and the lack of formal design codes at the time of their construction. Modern highways and railways have been designed and constructed to higher material specifications and geometries to suit the available construction materials. This means earthworks have an inherently higher factor of safety and are less vulnerable to changes in the groundwater level or surface water runoff due to underperforming drainage.

Rail and highways asset owners may prioritise drainage related works differently based on the level of risk that is tolerable to the safe operation of their infrastructure. The decision making process and how works are prioritised is covered in detail in Chapter 6.

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Box 1.1 Influence of drainage condition on earthwork stability (courtesy F Thomson, London Underground)

Earth structures C066 CTS1 and CTS2 form a 483 m length of cutting slope located on the Central Line between Barkingside and Newbury Park Stations in London. The cuttings reach a maximum height of 8 m, and stand at an angle of approximately 25° to 30°.

An analytical assessment of slope stability found these assets to have inadequate calculated factors of safety and recommended urgent remediation works. However, this was challenged, as the slope did not show any obvious signs of deep seated distress.

Further investigation established that the track drainage located at the toe of the cuttings was in poor condition with numerous blockages and reduced capacity due to collapses and tree root infestation. There was an indication that the poor condition of the toe drainage meant that water within the slope was not being effectively drained from the earthwork. Also because of this and following vegetation removal from the slope, a spring line (possibly natural) became visible along the toe of the cutting, just above the interface between the terrace gravels and the underlying cohesive low permeability London Clay. It was also suspected that due to root infestation some of the trees were feeding directly from the pipes, instead of from moisture in the soil and so were not contributing to the drainage of the slope.

The combined effect of these issues created the potential for pore pressures within the slope to become elevated and in turn have an adverse effect on slope stability. In advance of repair work, the site is now regularly monitored, with a standpipe piezometer installed.

In the long-term, an engineering solution such as a bored pile wall may still be required should it become necessary to improve the overall stability of the slope. However, significant improvements can be made by maintenance of the toe drainage and at the same time installing shallow slope drains

to intercept groundwater within the slope especially along the observed spring line. This would eliminate the need for immediate expensive slope stabilisation works by removing the principal factor resulting in deterioration of the slope condition.

The mass removal of trees on the cutting is generally not desirable due to their beneficial effects on stability. However, the trees in this case appear to be reducing the effectiveness of drainage within the slope with root reinforcement being the only beneficial effect. Any new or replacement drainage would require preventative measures against root ingress, eg by wrapping the drainage in a geotextile that is sufficiently robust to resist root penetration.

Figure 1.13 View of large tree (later removed) on cutting C066/CTS2 (courtesy London Underground)

Figure 1.12 View of cutting C066/CTS2 looking north on 10 February 2003 (courtesy London Underground)

Transport infrastructure drainage 9

Box 1.2 Highway drainage problems, Hertfordshire County Council (courtesy I Bone, Amey)

The A10 at Turnford, Hertfordshire is a two-lane dual carriageway. The surface of the carriageway began to deform severely at two locations on the nearside lane of the southbound carriageway. The carriageway sank and water was observed to pump out of the joints in the concrete slab under the weight of the passing traffic. Remedial work was carried out on several occasions but the patch repair did not last any significant length of time.

An investigation of the problem was inconclusive. There were never reports of standing water or excessive overland flow in this area. No cause for the build-up of water in the base layer was identified, however, the surface water drainage was found to have suffered long-term neglect. The gully connections had become silted up and may have caused infiltration into the lean concrete pavement base layer.

At another location the embankment toe ditches have been poorly maintained due to access difficulties. The embankment is heavily wooded and there was only limited space at the bottom for the ditch itself. It is almost impossible to get even the smallest form of machinery into the area. The only options available are to either hand-dig and remove the spoil by hand or to access the ditch from adjacent private land.

Lessons learnt:�� if routine drainage maintenance is neglected other assets

can suffer recurring damage�� drainage works should be designed to allow long-term

maintenance.

Figure 1.14 Pavement deformation (courtesy Amey) Figure 1.15 Patch repair failure (courtesy Amey)

Figure 1.16 Unmaintained toe ditch (courtesy Amey)

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1.2 puRpoSe AnD SCopeThis publication provides guidelines on good practice for the condition appraisal, maintenance and remedial treatment of transport infrastructure drainage, as well as advice on issues such as inspection, investigation and monitoring, asset management, health and safety and environmental issues. It also considers interaction with third party assets, and how transport drainage assets sit in the wider catchment. It includes references to appropriate standards and design guidance for renewals and remedial works.

The purpose of the guidance is to:

�� present current UK good practice (as of 2013) on transport infrastructure drainage (concentrating on roads and railways)

�� provide consideration of chambers, catchpits, inlets, outlets, pipes, filter drains, ditches, flumes, informal drainage, and ponds, and miscellaneous items such as interceptors and pumping stations

�� provide a guide for routine management of drainage assets

�� recommend current good practice on condition appraisal and remedial treatment strategies to give best value for money

�� raise knowledge and awareness of the connection between drainage asset performance and other key assets (such as the road pavement, track and geotechnical assets)

�� distil conclusions from existing UK and international research and practical experience on the whole life management of drainage assets

�� provide example case studies of good practice

�� facilitate knowledge sharing

�� identify gaps in knowledge or practice that will warrant future research and/or development, or standardisation.

What it is not:

�� it does not intend to duplicate areas covered in depth by Balkham et al (2010), and the reader is referred to this guide, particularly for coverage of the following topics:

�� how maintenance and remediation works should be ‘designed’ including catchment assessment and hydraulic aspects

�� environmental legislation and practice. The current document provides an overview of this legislation, and an update on recent or forthcoming legislation since the publication of Balkham (2010)

�� it is not a construction manual

�� it does not cover closed drainage infrastructure such as airports, or non-transport infrastructure such as systems related to housing, or sewerage systems

�� it does not cover specific aspects relevant only to tidal or coastal locations

�� it excludes consideration of the mechanical and electrical aspects of drainage assets such as pumps (although these are essential items in some drainage systems)

�� it excludes detailed consideration of filter media such as ballast and pipe surround materials (although it should be emphasised that these elements are essential components of the overall drainage system)

�� it does not attempt to define new, untried practices or principles.

1.3 AuDIenCeThis guidance is intended for:

�� drainage infrastructure owners and asset managers

Transport infrastructure drainage 11

�� organisations or individuals responsible for the routine maintenance and care of drainage assets

�� organisations or individuals who are responsible for assessment and remediation of drainage assets.

Document mapTable 1.1 directs the reader to the sections of the guide relevant to their area of interest:

Table 1.1 Document map

user Area of interest Relevant chapter

All readersGeneral issues relating to the management of drainage assets 1, 2

Case studies Appendix A1

Asset manager

Understanding responsibilities 1, 2, 5

Asset performance 3

Inspection and appraisal practices 4, Appendix A3

Maintenance and renewal procedures 7

Decision making 6

Infrastructure owner

Asset overview 1, 2

Responsibilities 2, 5

Decision making 6

Maintenance organisation

Asset performance 3

Inspection and appraisal practices 4, Appendix A3

Maintenance and renewal procedures 7, (and 5.2, 5.3, 5.5)

Decision making 6

Remedial works designer

Design issues 3

Maintenance and renewal procedures 7

Relevant design standards and guidance Appendix A2

Other interested parties

Understanding basic issues 1, 2

Case studies Appendix A1, boxes throughout the chapters

1.4 DeSCRIbInG The DRAInAGe ASSeTThere is no standardised set of nomenclature for describing drainage assets. Each infrastructure owner has its own terminology, and even within the standards and common use across an owner organisation there is inconsistency in terminology. At the detailed level the same terms can mean different things to different people. A high level grouping may be proposed based on asset geometry, function and construction as given in Table 1.2.

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Table 1.2 High level grouping of drainage asset types

Asset group Geometry function Construction example asset types*

Chambers Point asset

Subsurface transfer and maintenance point, connecting linear assets. Sometimes with a sump to trap sediment. Sometimes also for dispersal or temporary storage

Concrete, masonry or plastic chamber with cover, and incoming/outgoing pipe connections

Manhole, catchpit, inspection chamber, rodding eye, soakaway chamber, soakaway borehole, bifurcation or storm overflow, lamphole, attenuation tank, detention tank, storm tank, wet well

Gullies Point asset

Surface collection point connected to subsurface pipework. Generally with a sump to trap sediment

Small chamber with surface grating, sump and connection to carrier pipe

Gully (highway only)

Inlets and outlets Point asset

Transition point between surface and subsurface drainage

The point at which a below ground pipe flows from, or discharges into, a surface water course, with or without a headwall structure

Outfall, inlet, outlet, grip inlet

Pipes Linear asset

Subsurface water transfer, and in some cases also water collection

Below ground pipework, sometimes intentionally porous

Pipework, gravity drain, rising main, culvert, perforated pipe, porous pipe, siphon, land drainage, collector drain, drawdown drain, subhorizontal drain, carrier drain

Filter drains Linear assetSurface and/or subsurface water collection and transfer

A vertical gravel or synthetic filter medium with or without a basal pipe

Counterfort drain, combined surface and groundwater filter drains, filter drain, soakaway trench, fin drain, narrow filter drain, French drain, herringbone drain

Ditches and channel drains Linear asset Surface water collection

and transfer

Lined or unlined surface channels. Most types open, some enclosed

Ditch, grip, grassed surface water channel, swale, surface water channel, drainage channel block, edge channel, combined kerb and drainage channel, combined pipe and channel drain, linear drainage channel, channel drain, perforated channel drain, cascade, flume, aqueduct, conduit, crest drain, toe drain

Informal drainage Linear asset Off carriageway water

transfer No structure Over the edge

Ponds Polygonal asset

Water storage and in some cases also treatment or dispersal

A pond, lined or unlined or vegetated depending on function

Pond, detention basin, retention pond, sedimentation pond, infiltration basin, pollution containment pond or tank, wetlands, reed bed treatment system, bio-retention area

MiscellaneousPoint, linear or polygonal asset

Various Various

Flow control device, interceptor, oil separator, pumping station, reservoir pavement, cellular storage system, earthworks drainage blanket, ballast, blanket, baffle, flow restrictor, penstock, vortex flow control device

note

* the example asset types are defined in detail in the source glossaries listed in Table 1.3.

Transport infrastructure drainage 13

A common terminology across all UK infrastructure owners may be ultimately desirable, but in the meantime each asset owner should define a standard terminology, and should work towards adopting this terminology across its standards and guidance documents. To avoid ambiguities a glossary of standard terms should be available and illustrated with typical photographs or diagrams, so that all inspectors, surveyors and engineers are using the same terminology. Example glossaries are given in Table 1.3.

Table 1.3 Glossaries of drainage terminology

organisation Document defining drainage terminology

Highways Agency A drainage glossary available to download through the Highways Agency Drainage Data Management System website (HA DDMS) (see Useful websites)

Network Rail Railway Drainage Systems Manual. Part 1: Purpose, scope and general management requirements. Appendix A Glossary (NR/L3/CIV/005/1, 2010)

London UndergroundGuidance document – civil engineering – gravity drainage systems (G0052, 2012d)Civil engineering – gravity drainage systems (S1052, 2011a)

CIRIA Culvert design and operation guide (Balkham et al, 2010)

1.5 WhAT mAKeS DRAInAGe DIffeRenT?Unlike earthworks or structures, it is only recently that drainage has been considered as a separate asset and until this point pavement, permanent way and geotechnical engineers would include the drainage asset within their general remit. Clarity over ownership has been recognised as fundamental to improving the state of knowledge and condition of the drainage network.

1.5.1 Legacy of a ‘forgotten’ assetThe drainage asset is largely below ground and the above ground elements are often difficult to access, also construction records are often poor or non-existent. Visual inspections, such as that undertaken for earthworks, bridges and other civil assets, are only possible on a limited proportion of the drainage asset. Everywhere else requires lifting drain covers, man entry to confined spaces or CCTV camera surveys. This makes inspections slow and expensive.

Perhaps the access difficulty and expense associated with inspecting and maintaining the drainage assets has resulted in a system that is poorly understood, in terms of extent, condition and performance.

This is unfortunate as drainage is unlike any other asset – it has the potential to cause failures and reduce the life of virtually all other asset types. Indeed, it is alleged that the great Scottish engineer Thomas Telford once said “water is every civil engineer’s greatest enemy”. It has been realised now that there is a legacy of ageing drainage assets that can and have had a tremendous effect on other assets, consequently affecting organisational performance and system resilience. Most UK infrastructure owners now recognise the importance of drainage and are in the process of acquiring the detailed asset knowledge that will allow them to manage the asset more effectively (see Chapter 4).

1.5.2 Impact of flooding on transport operationsWhen drainage fails to function as intended there are direct consequences on the road or rail network. Some examples are presented here to illustrate the impact on operations:

�� a high proportion of floods on the transport network are due to failure or inadequate maintenance of the drainage asset. A Highways Agency internal study estimates that 60 per cent of carriageway flooding events are due to failure, blockage or underperformance of the highway drainage

�� on the UK rail network speed restrictions are put in place when water levels rise to within 50 mm of the top of rail level and line closure is considered when levels are 100 mm above the top of the track resulting in Network Rail having to pay penalty costs to the train operators. Between 2008 and 2011 Network Rail recorded between 200 and 500 flooding incidents each year causing about £50m of train delay costs per annum

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�� flooding of the road network affects road safety, directly causing accidents because of aquaplaning. DfT published accident statistics for 2011 show that 25 per cent of all traffic accidents occurred where the road was wet or flooded, causing over 50 000 injuries including 500 deaths. An unknown proportion of these incidents may be attributed to poor drainage management (see Useful websites)

�� flooding also causes delays to the travelling public, directly affecting journey time reliability, a core business driver for the Highways Agency and Network Rail.

1.5.3 Impact of drainage on other assets and adjacent propertyThe drainage asset has a direct or indirect effect on other infrastructure assets, as illustrated in Figure 1.17.

Figure 1.17 Asset interactions and consequences of failure (after Network Rail, 2012a)

One of the most significant impacts is the interaction of drainage with earthworks. Slope failures can result when the water pressures within the slope build-up due to the in-slope drainage becoming blocked and ceasing to function, or because there is insufficient slope drainage to control the water pressures. Direct washout failures in cutting slopes occur in a rapid and often catastrophic manner.

The Highways Agency estimates that 70 per cent of earthworks failures are directly or indirectly due to drainage related issues. London Underground estimates the vast majority of significant failures over the last 20 years have been drainage related. Investigations into the train derailment at Moy, Inverness-shire in 2005 found that an earthwork failure resulted from changes made to adjacent third party land. The construction influenced the performance of the local drainage systems at the site and increased the surface water standing on, and flowing from, the non-railway land following a period of localised extreme weather, which in turn caused a landslip on the railway cutting slope. Investigations into another derailment at Gillingham tunnel in Dorset caused by a landslip, attributed the cause to a blocked ditch at the top of a cutting slope (see Box 1.3).

Transport infrastructure drainage 15

Box 1.3 Derailment near Gillingham tunnel, Dorset 28 November 2009 (courtesy RAIB)

Structures are also at risk. Drainage is designed to reduce the build-up of water pressures on the back of retaining walls, and inadequate drainage or blockages can lead to serviceability issues and potentially failure, as illustrated in the following examples:

�� London Underground reported a failure of a cutting behind retaining walls in 1954 at Uxbridge (Watson, 1956). Watson demonstrated through back-analysis that the factor of safety of the wall was strongly influenced by the level of water behind the wall (ie the application of the principles of effective stress). Remedial works incorporated new piped drainage at the rear of the wall tied to counterfort drains on the slopes. In response to the slip soil mechanics director Dr H Golder stated that “all engineers dealing with banks knew the important rule was drainage and more drainage”

�� the build-up of pore water pressures was also attributed to a Network Rail tunnel portal and retaining wall collapse in 2002 at Carmuirs, near Falkirk, Scotland. At this location, changes in the drainage regime, through successive developments in the locality, were likely to have been at the root cause of the collapse.

The immediate impact is less than for earthworks, but the long-term consequence of ineffective drainage on pavement and track manifests as poor ride quality, speed restrictions and shortened lifespan. Network Rail figures submitted to the Office of the Rail Regulator (ORR) indicate that up to three times as much track maintenance work is carried out on track where drainage is in poor condition, compared with locations where drainage is well maintained. For roads, the Transport Research Laboratory (TRL) estimates that 10 per cent of premature pavement failures are due to inadequate or ineffective drainage of the foundation layers failing to prevent saturation. An example of where drainage has caused premature pavement failure on an inner city tram system is given in Case study A1.8.

The nature of drainage means that assets often cross ownership boundaries, so that storm surges or spillages originating in one owners responsibility may result in flooding or pollution of another owner’s infrastructure. Section 2.4 and 2.7 provides more information on rights and responsibilities where this situation occurs, and an example is given in Case study A1.2.

Pollution of surface watercourses or the groundwater regime can also occur through inadequate design (lack of pollution controls), poor maintenance (non-functioning pollution control devices) or lack of asset knowledge (emergency response teams targeting the wrong outfall during a pollution incident). Environment Agency (EA) statistics show that between 2002 and 2008 there were 239 major (EA Category 1 and 2) pollution incidents on the transport networks in England and Wales. An unknown proportion of these incidents may have been due to, or exacerbated by, drainage related issues.

1.5.4 Impact of other assets on drainageAs discussed in Section 1.5.3, drainage can affect other assets to the detriment of safety, performance and asset life expectancy. The reverse is also true as indicated in Figure 1.17. A poorly designed or maintained earthwork or pavement can affect the structural and hydraulic performance of the drainage infrastructure. Management of the vegetation is particularly relevant here as the impact of unchecked growth, direct root damage and vegetation induced shrink-swell movement of susceptible cohesive soils can lead to performance deterioration of both piped and surface drainage assets (see Section 3.4.2).

During the evening of 28 November 2009, a London to Yeovil train ran into a landslip in a cutting on the eastern approach to Gillingham tunnel in Dorset. The leading carriage of the train became derailed and the train ran into the tunnel and stopped 200 m inside. The landslip was caused by water overflowing from a blocked ditch at the top of the cutting slope. Two passengers reported minor injuries. The leading carriage of the train and around 450 m of railway track were damaged.

The Rail Accident Investigation Branch (RAIB) undertook an investigation into the incident and made five recommendations to Network Rail relating to management of drainage and earthworks. These include a recommendation to identify, and then adequately maintain, drainage, which is required for railway safety but is not located close to the railway tracks.

The investigations concluded that poor performance of ‘off track’ drainage resulted in failure of the interfacing adjacent earth structure asset.

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Poorly installed cabling, troughing, safety barriers or lineside furniture can disrupt or severely damage the drainage system (see Section 3.7.1).

1.5.5 Infrastructure resilienceThere is increasing understanding in the wider engineering community of the importance of ‘system resilience’. When the drainage is overwhelmed by heavy rain the direct impact on the transport infrastructure is flooding. However, there are indirect, and sometimes longer term, impacts outlined in Section 1.5.3. The transport sector enables mobility of goods and people, so any flooding or indirect failure of associated infrastructure can affect transport system reliability, and ultimately on the performance of the UK economy. Further information is available in McBain et al (2010).