Hard copy available in
Needs Report
Box 60
Folder A
January 2013
Re po rtApplication for Development Consent
Application Reference Number: WWO10001
Doc Ref:
8.3
Main Report
THAMES TUNNEL
NEEDS REPORT
LIST OF CONTENTS Page Number 1 EXECUTIVE SUMMARY 1 1.1 Introduction 1 1.2 Historical context 11.3 The modern River Thames 1
1.4 Legal requirements 2
1.5 TTSS report, recommendation and EA view 2
1.6 Regulatory Impact Assessment and Minister’s 2007 request 3
1.7 Work since the 2007 Ministerial request 3
1.8 Investigation of solutions used elsewhere in Europe 4
1.9 Written ministerial statements in 2010 4
1.10 Conclusions 5
2 INTRODUCTION 6
2.1 Background 6
2.2 Purpose of this report 7
2.3 Report structure 8
3 THE LEGAL AND REGULATORY CONTEXT 9
3.1 Introduction 9
3.2 Sewer systems and governing legislation 9
3.3 Overview of regulatory framework within which the water and sewerage
undertakers operate 10
3.4 Urban Waste Water Treatment Directive and related UK Regulations 11
3.5 Statutory duties of the water and sewerage undertakers 13
3.6 The Water Framework Directive and associated requirements 14
3.7 Powers of the European Commission to bring infraction proceedings 17
4 THE NEED 18
4.1 London’s sewerage 19
4.2 The Thames Tideway Strategic Study and further work by Thames Water 21
4.3 Baseline conditions 23
4.4 Model development work undertaken since the TTSS 23
4.5 CSO performance 24
4.6 The legal need - UWWTD, WFD and other statutory duties 32
4.7 Water quality impacts 36
4.8 Further considerations 43
4.9 The long term effect of ‘doing nothing’ 45
4.10 Summary of the need 46
5 ACHIEVING COMPLIANCE 47
5.1 London Tideway Tunnels 47
5.2 Design and Performance Criteria 47
5.3 Tunnel options 49
5.4 Alternative approaches to the tunnel options 55
5.5 Further considerations 66
5.7 Related work 74
6 OVERVIEW AND CONCLUSIONS 76
6.1 Legislation and European Commission Actions 76
6.2 Background and the TTSS 76
6.3 Government response to the TTSS studies in 2007 76
6.4 Tunnel options and alternatives 77
6.5 Conclusion 77
ABBREVIATIONS 79
GLOSSARY 81
REFERENCES 84
APPENDICES (in separate volume) 86
APPENDIX A: MINISTERIAL CORRESPONDENCE, REGULATORY IMPACT ASSESSMENT APPENDIX B: REPORT ON APPROACHES TO UWWTD COMPLIANCE IN RELATION TO
CSOs IN MAJOR CITIES ACROSS THE EU APPENDIX C: POPULATION STATISTICS
APPENDIX D: SEWER SEPARATION FEASIBILITY STUDY
APPENDIX E: POTENTIAL SOURCE CONTROL AND SUDS APPLICATIONS APPENDIX F: TIDEWAY FISHERIES REVIEW
LIST OF FIGURES
Page Number
Figure 4.1 Catchment areas draining to Mogden, Beckton and Crossness STWs ... 19
Figure 4.2 Locations of discharges on the Thames Tideway ... 19
Figure 4.3 TTSS Option 1c ... 23
Figure 5.1 London Tideway Tunnels: Alignment Options ... 51
Figure 5.2 Comparison of Dissolved Oxygen Standard Compliance – (a) No improvements, (b) STW improvements and Lee Tunnel, (c) River Thames/ Rotherhithe route and (d) Abbey Mills route ... 53
LIST OF TABLES Page Number Table 4.1 Comparison of annual spills at existing, intermediate and projected baseline conditions ... 25
Table 4.2 Comparison of projected CSO performance during a typical year, before and after commissioning of Lee Tunnel and STW Improvements ... 27
Table 4.3 Revised interim EQS for DO on the Tideway, derived by the TTSS Steering Group and the Environment Agency ... 38
Table 4.4 Comparisons of WFD Standards (shaded rows) and Tideway EQS for DO ... 40
Table 4.5 Summary of UK climate change predictions UKCIP02 and UKCP09 ... 42
Table 5.1 Comparison of overflow volume and number of spills for tunnel route options ... 52
Table 5.2 Comparison of tunnel alignments ... 54
Table 5.3 Cost estimates1 (£ millions) for each tunnel alignment ... 55
Table 5.4 TW asset data: Sewers categorised as combined ... 56
Table 5.5 Allowances for non-construction costs ... 58
Table 5.6 Total costs for each sewer separation study area ... 58
Table 5.7 Summary of CSO discharge volume (m3) for December event of the typical year during the 1-year 120m-min storm event for the expanded STWs and the 2021 population ... 60
Table 5.8 Total costs for each source control/SUDS study area ... 63
Table 5.9 Advantages and Disadvantages of options ... 64
Table 5.10 Summary of main options and estimated costs ... 65
Table 5.11 Percentage reduction in annual spill volumes and frequencies ... 68
Table 5.12 Estimated quantities of sewage litter entering the Thames Tideway (tonnes) ... 69
Table 5.13 Approaches to UWWTD compliance in relation to CSOs in major cities across the EU ... 72
1 EXECUTIVE SUMMARY 1.1 Introduction
The Thames Tunnel is a full-length storage and transfer tunnel proposed to intercept discharges from overflows into the tidal Thames from West to East London and to pass them for treatment at Beckton Sewage Treatment Works. The primary objective of the Thames Tunnel is to capture discharges from Combined Sewer Overflows (CSOs) into the River Thames in order to meet the requirements of the EU Urban Waste Water Treatment Directive and the related UK Urban Waste Water Treatment Regulations.
The Needs Report considers the need for the Thames Tunnel taking into account the Lee Tunnel and the other London Tideway Improvements (LTI), namely the sewage treatment works upgrades. It builds upon work undertaken for the purpose of the Thames Tideway Strategic Study (TTSS), as reported in February and November 2005, and the further report “Tackling London’s Sewer Overflows”, as issued in December 2006.
1.2 Historical context
London’s sewer system was designed in the 1800s to handle waste water and run-off rainwater through a combined collecting system. CSOs were incorporated into the sewer system as relief structures to prevent flooding caused by sewer overloading, especially during periods of heavy rainfall.
Much of London’s sewerage infrastructure consists of combined systems, whereby a single set of sewers convey both foul sewage and rainwater runoff to a sewage treatment works for treatment. The current sewer system is subject to significant flows from surface drainage and so generates large volumes of storm sewage (sewage and rainwater mixed). This is in part due to historic watercourses having been used for sewage disposal and subsequently culverted as the density of development intensified. Rainfall causes combined sewer systems to surcharge quickly. For this reason, it is normal practice to incorporate overflows that allow excess flows to discharge directly to a watercourse to reduce flood risk to properties and prevent overloading the sewerage system. The capacities originally allowed for in the interceptor sewer systems originally designed by Sir Joseph Bazalgette in the 1850s and subsequently extended have now been substantially exceeded. Despite improvements over the years there is little spare capacity in the sewerage network as a whole. This is largely due to the increases in population, water usage and increased hardstanding areas served. This greater proportion of hard surfacing has reduced the capability of the land to absorb rainwater which instead now enters the sewerage network such that it now only takes as little as a few millimetres of rainfall to cause some CSOs to discharge storm sewage into the River Thames.
1.3 The modern River Thames
Currently, spillages to the tidal Thames occur more than 50 times per year at the most frequently overflowing CSOs in the Beckton and Crossness catchments, north and south of the river
respectively. An estimated total of some 39 million cubic metres of storm sewage enters the river in a typical year from these catchments. In a wet year this volume can be much greater, but will otherwise reduce to some 18 million cubic metres by 2015 on completion of the sewage treatment works upgrades and the Lee Tunnel. The Beckton and Crossness drainage catchments are the principal source of storm sewage discharges to the tideway, and there are no significant CSOs discharging to the tidal River Thames west of Acton, As reported by the Minister for Climate Change and the Environment (Ian Pearson) in the Written Ministerial Statement (Hansard 22 Mar 2007: Column 53WS):
“These overflows are having an adverse effect on the environmental quality of the Thames. It has been found that the frequent overflows (on average once a week) and the large quantities of untreated discharges are causing:
Adverse environmental impacts on fish species; Unacceptable aesthetic issues; and
Elevated health risks for recreational users of the Thames.”
The situation in London is exacerbated by the characteristics of the Thames river basin and the estuarine reach of the river Thames. Water moves up and down the river, with the incoming and outgoing tides, with the net seaward movement taking up to three months to travel along the estuary from Teddington to Southend. Summer storms in particular have the potential to cause greatest impact, due to (a) low natural flows in the river meaning less dilution of the overflows, and (b) higher water temperatures meaning the river contains less dissolved oxygen to sustain aquatic life and what dissolved oxygen is present is consumed more quickly.
Should nothing be done to address the current situation, continuing population growth and
incremental increases to impermeable areas are expected to increase the volume and frequency of discharges to the river. Such increased discharges will have associated increased adverse
environmental impacts.
1.4 Legal requirements
The Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors. The objective of the Directive is to protect the environment from the “adverse effects of the above mentioned waste water discharges”. The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI1994/2841) transpose the UWWTD into English law. Annex 1 of the UWWTD (and repeated in the Regulations) includes the following requirements for collecting systems:
The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding:
volume and characteristics of urban waste water, prevention of leaks,
limitation of pollution of receiving waters due to storm water overflows.
Infraction proceedings are being pursued by the European Commission against the United
Kingdom for breach of the UWWTD. On 8 October 2009 the European Commission announced its decision to take the United Kingdom to the European Court of Justice on the grounds that urban waste water collecting systems and treatment facilities in London (and Whitburn) do not comply with EU legislation.
Other EU and UK legislation also forms part of the legal framework within which the Thames Tunnel is to be designed and delivered. The Water Framework Directive (WFD), and the
regulations which transpose it within the UK, set out various ‘environmental objectives’ relating to surface water quality to be achieved by 2015, 2021 and 2027. In order to achieve these objectives in the UK, the Environment Agency has responsibility for the production of river basin management plans. The River Basin Management Plan for the River Thames, published in December 2009, states that the London Tideway Tunnels (the Thames and Lee Tunnels); “represent the primary measures to address point source pollution from the sewer system and are fundamental to the achievement of good status in this catchment” (Estuaries and Coastal Waters Catchment). The Thames Tunnel is therefore required to help to achieve compliance with the WFD as well as with the UWWTD.
1.5 TTSS report, recommendation and EA view
The Thames Tideway Strategic Study (TTSS) was set up in 2001 and reported in February and November 2005. This Steering Group was established under the independent chairmanship of Professor Chris Binnie. Its members included representatives from Thames Water, the EA, DEFRA, the GLA and Ofwat, the latter with observer status. Its purpose was to assess the environmental impact of intermittent discharges of storm sewage on the Thames Tideway, to identify objectives for improvement and to propose potential solutions, having regard to costs and benefits.
As part of the TTSS the Environment Agency (EA) assessed the CSO discharges from the Beckton and Crossness catchments. The EA considered the volume and frequency of the different
discharges, as well as assessing their impact on river water quality and ecology. These were then categorised on the basis of criteria including frequency and volume of discharge. A total of 36 CSOs were identified as being unsatisfactory and therefore requiring attention, of which 34 discharge to the Tidal Thames and two into the River Lee.
Specific environmental objectives were developed by the TTSS which needed to be addressed by the project, namely to reduce:
the adverse environmental impacts on the river ecosystems and on fish species in particular;
the unacceptable aesthetic issues; and
the elevated health risks for recreational users of the tidal Thames.
The TTSS established that the environmental objectives can only be met at least cost by
completing both quality improvements to the treatment works discharges and by the provision of a storage and transfer tunnel to intercept unsatisfactory CSOs.
Ofwat commissioned Jacobs Babtie to review the TTSS. The principal output of this work was an alternative solution, based on two shorter tunnels (one in West London and one in East London), along with further recommendations.
DEFRA considered the various reports and asked Thames Water to provide cost information on the identified tunnel solutions.
1.6 Regulatory Impact Assessment and Minister’s 2007 request
The TTSS and subsequent studies, including the Jacobs Babtie report, were considered by Defra and a Regulatory Impact Assessment was issued in March 2007. The Regulatory Impact
Assessment specifically rejected the solution identified by Jacobs Babtie as it did not meet the required regulatory or TTSS environmental objectives.
Ian Pearson, the then Minister of State for Climate Change and the Environment, in a letter to the Chief Executive Officer of Thames Water dated 17 April 2007, stated that his view was that: “a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment
works – is needed. This is both to provide London with a river fit for the 21st century, and for the
UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water overflows.” Furthermore, Ian Pearson subsequently requested that Thames Water “make provision for the design, construction, and maintenance of a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works which involves a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works”.
(Letter reproduced in full at Appendix A, Item A1.1)
1.7 Work since the 2007 Ministerial request
Since the Ministerial request in 2007, Thames Water has responded to the request. Its work has included the following activities:
1.7.1 Modelling
Thames Water maintains a numerical hydraulic model that represents the sewer system for the Beckton and Crossness catchments. This model has continued to be developed since 2006. As part of the model development work, a programme of flow monitoring of the system has been implemented, including monitoring at CSO locations.
In parallel with the hydraulic model, a water quality model of the Thames Estuary from Teddington weir to Southend was developed for the Environment Agency (EA) to understand the impacts on water quality of discharges from sewage treatment works (STWs) and CSOs.
The catchment and water quality models were used to test the impacts of various proposed options. Climate change projections have been taken into account. The models have
demonstrated that the ‘do nothing’ option is unacceptable. The modelling has also confirmed that the addition of the full-length storage tunnel is necessary to achieve the required reduction in the frequency and volume of CSO discharges. Such a reduction is the key outcome to enable
compliance with the UWWTD. The tunnel will also contribute towards achieving the WFD objective to attain good ecological potential in the Thames Tideway.
1.7.2 Refinement of the Scheme
Considerable development work has been undertaken since 2007 to refine the full-length storage tunnel scheme. Three alternative tunnel alignments have been studied, namely the River Thames route (very similar to the original concept), the Rotherhithe route and the Abbey Mills route. All three alignments will contribute towards achieving the EA water quality standards and the TTSS environmental objectives whilst achieving the requirements of the UWWTD. However, the shorter Abbey Mills route offers the lowest cost and least adverse environmental and community impacts when compared to the other two routes. It is therefore recommended as the preferred route.
1.7.3 Investigations into sewer flooding
Flooding of basements, gardens and roads occurs in parts of London during or following major rainfall events, caused by surcharging of combined sewers. A number of projects are planned to alleviate this sewer flooding. Once the storage tunnel has been developed and is in operation it will be a strategic component of London’s infrastructure and will provide flexibility to adapt the network for future conditions, including opportunities for the flows from new sewerage
infrastructure to be diverted to the tunnel.
1.7.4 Consideration of alternative options
Alternative technologies have been explored such as source control (methods of managing and reducing storm water runoff at site level), sewer separation (separate storm water and foul networks), partial separation, dispersed storage units (capturing storm water and controlling the outflow), CSO screening and sustainable drainage systems (SUDS) (techniques employing ponds, swales, ‘green’ roofs, detention ponds and permeable surfaces).
None of these options have been found to be suitable cost effective solutions when compared to the full-length storage tunnel solution or capable of meeting the requirement to achieve compliance with the UWWTD by the target date of 2020 (the date provided by the UK Government to the European Commission) and meet the TTSS environmental objectives. Also these alternative options will not assist in meeting the WFD objective to attain good ecological potential in the tidal Thames.
1.8 Investigation of solutions used elsewhere in Europe
Most major cities in the European Union have had or are having to address the issue of CSO discharges from their sewer networks. A review of the approaches to UWWTD compliance in relation to CSOs by certain major and many smaller cities across the EU has demonstrated that the most common approach to resolving CSO issues was the addition of extra capacity by the construction of detention tanks and/or trunk or interceptor sewers. Cities such as Helsinki, Naples, Stockholm and Vienna already use tunnels to resolve their CSO issues. Paris, like London, is developing a tunnelled storage and conveyance system to meet the requirements of the UWWTD.
1.9 Written ministerial statements in 2010
In a written statement to Parliament on 1 March 2010 the then Secretary of State for Environment, Food and Rural Affairs (Hilary Benn) announced that he was minded to direct planning applications for the tunnel to the Infrastructure Planning Commission. In doing so he set out the case for the Thames Tunnel as a project of national significance which, if not implemented, could cause reputational risk to the UK. The Secretary of State commented that the urgency of the works is
increased by the infraction proceedings being pursued against the UK by the European Commission for an alleged breach of the UWWTD.
The succeeding Environment Secretary, Caroline Spelman, issued a written ministerial statement on 7 September 2010 confirming the coalition government’s support for the construction of the tunnel from West London to Beckton and declaring that “a Thames Tunnel continues to offer (by far) the lowest cost solution to the problem and I believe Thames Water should continue to press forward with this project working with Ofwat, the Environment Agency and Defra on the regulatory, commercial and planning processes”.
The Environment Secretary’s statement added that “I am also minded that development consent for the project should be dealt with under the regime for nationally significant infrastructure projects established by the Planning Act 2008. I consider that this project, with its unique scale and
complexity, is of national significance, and therefore appropriate for this regime”. (Written ministerial statement reproduced in full at Appendix A, Item A1.2) 1.10 Conclusions
Thames Water has been requested by successive UK Governments to make provision for the design, construction, and maintenance of a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works which includes a full-length storage tunnel with additional secondary treatment at the Beckton STW.
The Thames Tunnel would meet these Ministerial requests. Delivery of such a scheme also provides benefits in improved water quality, aesthetics, health of recreational users and the sustainability of the aquatic environment in the Thames Tideway. It will also contribute towards achieving the UK’s WFD objective to attain good ecological potential in the tidal Thames. The recommended full-length storage tunnel (Abbey Mills route) achieves compliance with the UWWTD and environmental objectives. At an estimated cost of £3,588 million it is the most cost effective scheme, involving the least disruption to residents, businesses and transportation when compared to alternatives. It also has the shortest implementation time which will facilitate the target date of 2020. The UWWTD provides that “The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs”. It is concluded that the full-length storage tunnel approach on the Abbey Mills route is the most cost effective solution which meets the requirements of the UWWTD and the environmental objectives.
2 INTRODUCTION
The primary objective of the Thames Tunnel is to capture flows discharging from
CSOs into the River Thames to meet the requirements of the EU Urban Waste Water Treatment Directive.
The quality of the Tidal Thames has been the subject of studies over a considerable
period of time. These have been driven by increasing environmental expectations and obligations arising from the interpretation of successive European Directives.
Mitigation of poor river water quality has been provided in several ways. In 2001 the Thames Tideway Strategic Study (TTSS) was set up to assess the impacts of
intermittent discharges of combined storm and foul sewage on the Thames Tideway.
The TTSS was co-ordinated by a Steering Group chaired by the independent
Professor Chris Binnie with representatives from EA, Defra, GLA and Thames Water. The TTSS reports, published in 2005, recommended improvements to both collecting systems and treatment works, and proposed targets for water quality. These reports have formed the basis of all subsequent work.
For the TTSS the EA categorised the 57 CSOs relating to the Beckton and Crossness
sewer catchments (collecting systems) and identified 36 as unsatisfactory and
requiring improvement. Of these, 34 discharge directly to the River Thames. There are no CSOs requiring improvement situated west of Acton.
Subsequent work, presented in Tackling London’s Sewer Overflows, Thames Tideway
Tunnel and Treatment – Option Development, Summary Report (December 2006),
developed a preferred solution, referred to as Option 1c, to intercept 36 unsatisfactory CSOs into a full length storage and transfer tunnel to convey flow to treatment at Beckton STW.
Aside from the Thames Tunnel, other related improvements, including the Lee Tunnel
and improvements to the STWs at Mogden, Beckton, Crossness, Riverside and Long Reach are now under construction.
This report focuses on the need for the Thames Tunnel as part of the above suite of
measures required to comply with European legislation and achieve environmental objectives. It is intended to assist the consultation process.
2.1 Background
Substantial proportions of London‘s sewerage network were built on the ‘combined‘ principle, whereby a single set of sewers convey foul sewage, groundwater infiltration and rainwater runoff to sewage treatment works (STWs) for treatment, prior to discharge to the Thames Tideway. It is normal practice for combined sewer systems to incorporate overflows in the system, known as combined sewer overflows (CSOs). CSOs allow excess storm flows following rainfall to discharge directly to a water body to reduce flood risk to land and properties. This is the case with much of the London sewer system which has been extended over the years and now incorporates 57 CSOs in the Beckton and Crossness catchments which discharge to the Thames Tideway and lower River Lee.
The impact of these discharges only began to be appreciated in the late 1970s when general improvements to sewage treatment improved the background water quality to the point where fish populations were able to re-establish. Operation of these overflows under certain conditions, particularly summer conditions of low natural river flows and high temperatures, could result in localised deoxygenation and fish deaths. Mitigation measures have been adopted to help maintain oxygen concentrations and these have been largely successful in avoiding major or frequent fish mortalities but these have always been recognised as ameliorating the impact.
Recognising the causes and impacts of these episodes of poor water quality the Tidal Thames has been the subject of the many studies over a considerable period of time. These have been driven by increasing environmental expectations as well as obligations arising from the interpretation of successive European Directives. Nonetheless, it was clear that a major study would be required
and this was endorsed in 2000, leading to the establishment of the Thames Tideway Strategic Study (TTSS).
The Steering Group of the TTSS was assembled in early 2001 to co-ordinate the study, to assess the environmental impact of intermittent discharges of combined storm and foul sewage on the Thames Tideway, to identify objectives for improvement and to propose potential solutions, having regard to benefits and costs. Thames Water (TW), the Environment Agency (EA), Department of Food and Rural Affairs (Defra) and the Greater London Authority (GLA) were represented on the Steering Group under the independent chairmanship of Professor Chris Binnie. The Water Services Regulation Authority (Ofwat) maintained an observer status. The Steering Group was supported by three working groups focussed respectively on Objectives, Cost-benefits and Solutions.
As part of the TTSS the EA evaluated 57 CSOs in the Beckton and Crossness catchments by considering the volume and frequency of the discharges, as well as assessing their impact on river water quality and ecology. These were then categorised and a total of 36 CSOs were identified as being unsatisfactory and therefore requiring control. Of these, 34 discharge directly into the tidal River Thames and the other two into the tidal River Lee. The remaining 21 CSOs were assessed by the EA as not requiring any action to be taken. Of the two unsatisfactory CSOs discharging into the River Lee one is being addressed by the provision under a related, but separate, scheme of a 7km long, 7.2m diameter storage tunnel from Abbey Mills Pumping Stations to Beckton Sewage Treatment Works (STW). This is referred to as the Lee Tunnel. A local improvement solution is adequate for the other CSO.
West of Acton there are no significant CSOs discharging to the tidal River Thames from the Beckton and Crossness catchments. Much of the pollution in the Richmond area of the River Thames originates from the CSOs downstream and reaches the area on the incoming tide. While the catchments served by Beckton and Crossness sewage treatment works to the east have a substantial proportion of combined sewers, the area in the west of London that drains to Mogden STW contains mostly separate sewers for rainwater and sewage. The Mogden sewerage network is, therefore, less responsive to rainfall and the volume of discharges in the area is small in comparison to those downstream. As part of the London Tideway Improvements significant works are under way at the Mogden STW to increase the secondary treatment capacity of the works and so reduce the frequency of overflow from the storm water settlement tanks that already exist as part of the treatment plant. Consequently there is no water quality justification, nor legislative driver, to extend the proposed tunnel west of Acton.
Following on from the TTSS and an independent review by Jacobs Babtie, further study by
Thames Water recommended that, in conjunction with the London Tideway Improvements and Lee
Tunnel schemes, a single tunnel option, described as the Thames Tunnel Option 1c1, was the
optimal solution satisfying both policy frameworks and statutory requirements, including European requirements, in a phased programme of works. The study culminated with a policy decision by the responsible Minister, in support of a full-length storage tunnel.
The ‘Thames Tideway Sewer Tunnel Project’ is supported in the London Plan (2008) (Policy 4A.18), the draft Replacement London Plan, December 2009 (Policy 5.14), the Mayor’s draft water strategy, 2009 (Proposal 10), and some local development framework core strategies produced by London Boroughs.
2.2 Purpose of this report
This report sets out the latest position on the need for the Thames Tunnel in the light of further work since the publication of the Thames Tideway Tunnel and Treatment Summary Report in December 2006, including the improvements to the hydraulic modelling of the contributing catchments. It also takes account of the Lee Tunnel Project and the London Tideway
Improvements schemes currently being implemented. The Thames Tunnel Needs Report will also assist in the consultation process for the Thames Tunnel.
1 Tackling London’s Sewer Overflows, Thames Tideway Tunnel and Treatment – Option
2.3 Report structure
The document has been structured as follows:
Section 3 provides the legal and regulatory context.
Section 4 documents the need for a solution to meet the regulatory drivers and outlines the
risks of doing nothing.
Section 5 establishes a solution to achieve compliance examines other alternatives and
outlines the benefits of the solution including its flexibility for facing future climatic conditions, population growth, water demands and changes in environmental requirements. It also provides information on the solutions being promoted to comply with the EU Directives elsewhere in Europe.
Each of the above chapters is headed by a summary box which sets out the key issues covered within that chapter. These chapter summaries are intended to assist the reader in their
understanding of the Needs Report.
Section 6 provides an overview of the key issues and conclusions.
Lists of the abbreviations, a glossary of terms and the references used are located at the
end of the report.
3 THE LEGAL AND REGULATORY CONTEXT
This section sets out the major driver for the Thames Tunnel, this being compliance
with the legislation summarised below.
The objective of the Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) is
to protect the environment from the “adverse impacts of insufficiently treated waste water discharges”.
Subject to a caveat that not all flows can be treated under situations such as
unusually heavy rainfall, there is a presumption in UWWTD that all sewage collected will be treated to secondary standard prior to discharge, and that pollution due to stormwater overflows will be limited.
In the event that the UK is found by the European Court of Justice to have failed to
fully implement Directives (including UWWTD), then substantial financial penalties may be imposed on the UK.
The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI 1994/2841)
transpose the UWWTD into UK law. Failure to address identified obligations would expose water and sewerage undertakers to the risk of enforcement action from the UK Government and/or Regulators.
The Water Framework Directive (WFD) (2000/60/EC) aims at maintaining and
improving the aquatic environment in the Community. The Directive was transposed into UK law by the Water Environment (Water Framework Directive) (England and
Wales) Regulations 2003 (SI 2003/3242). The WFD requires that Member States aim to
achieve, subject to caveats, Good Ecological Status (GES) or, in the case of heavily modified waterbodies such as the tidal Thames, Good Ecological Potential (GEP) by 2015.
Legislation therefore requires action to be taken to address CSO discharges which
are found to cause adverse effects on the receiving watercourse and/or operate outside of adopted criteria.
The legal framework for the required action is complemented by the economic
framework regulated by the Water Services Regulation Authority (WSRA), known as Ofwat, and the environmental standards set and monitored by the Environment Agency (EA).
3.1 Introduction
This section provides an overview of the law as it generally relates to sewerage and sewage disposal. Water and sewerage undertakers have a statutory duty to comply with the law and their activities are regulated, monitored and overviewed by various government established bodies to protect the environment and the interests of consumers. Specific details relating to Thames Water, the Thames Tideway and the Thames Tunnel in particular are covered in later sections.
3.2 Sewer systems and governing legislation
Sewer systems are necessary in urban environments to remove both waste water and storm water from areas of habitation. Waste water may be defined as the flow originating from water closets and other domestic and industrial sources, while storm water is derived from rainfall falling on the catchment. Urban sewer systems are designed to handle waste water and storm water, while minimising their risk to human life and the environment. Two basic types of conventional sewer systems exist: combined systems, where waste water and storm water flow together, and separate systems where waste water and storm water are kept apart.
Insufficient provision for drainage can lead to disease, inconvenience, damage, flooding and pollution. Consequently, regulations have been set in place, with the aim of providing measures that prevent and reduce the risk, and/or extent, of these undesirable consequences.
Three pieces of legislation are specifically related to sewers and their discharges:
The Water Industry Act 1991 - to provide, improve and extend a system of public sewers and
dealing with their contents.
The EU Urban Waste Water Treatment Directive 1991 (transposed into UK regulations) sets
out more specific standards on the discharge requirements from waste water treatment plants and the general requirements for collecting systems.
The UK Water Resources Act 1991 - regulating discharges to controlled waters to avoid
pollution. Controlled waters include rivers, estuaries, coastal waters, lakes and groundwaters. Discharge to controlled waters is only permitted with the consent of the Environment Agency.
3.3 Overview of regulatory framework within which the water and sewerage undertakers
operate
Water and sewerage undertakers are private companies, answerable to shareholders, which operate within a regulatory framework under the auspices of the UK Government’s Department for Environment, Food and Rural Affairs (Defra). The regulators are the Water Services Regulation
Authority(WRSA), the Drinking Water Inspectorate (DWI) and the Environment Agency (EA), each
covering differing aspects of the statutory services and activities. The water consumers are represented by the Consumer Council for Water (CCW).
3.3.1 The Water Services Regulation Authority (Ofwat)
The Water Services Regulation Authority, referred to as “Ofwat” throughout this report, is the economic regulator of the water and sewerage undertakers in England and Wales. It ensures that the water and sewerage undertakers provide household and business customers with a good quality service and value for money. Ofwat regulates the 21 regional monopoly water and sewerage undertakers in England and Wales. This involves, inter alia:
making sure that the water and sewerage undertakers provide customers with a good
quality, efficient service at a fair price.
establishing challenging efficiency targets for each water and sewerage undertaker, as part
of setting a final price determination (establishing how much can be charged to customers), and including an investment and expenditure programme known as an Asset Management Plan (AMP). Each plan is for a five year period. AMP5 is the plan for the period 2010 to 2015.
monitoring the companies’ performance and taking action, including enforcement, to protect
consumers’ interests
Requiring each company to plan forward and establish 25-year investment strategies and to
put each AMP plan within this context. The 25-year plans should take into account, among other considerations, changes in legislation, household consumption, population, river water quality and environmental enhancements.
Ofwat uses a network of independent reporters to assist them in monitoring the performance of the water and sewerage undertakers, assessing their efficiency and checking the quality of data provided.
3.3.2 Drinking Water Inspectorate (DWI)
The main job of the DWI is to check that the water and sewerage undertakers in England and Wales supply water that is safe to drink and meets the standards set in the Water Quality
Regulations. Inspectors carry out technical audits of each water company. The DWI is not involved in sewerage and waste water treatment regulation.
3.3.3 Environment Agency (EA)
The Environment Agency is an executive non-departmental public body responsible to the Secretary of State for Environment, Food and Rural Affairs (Defra) in England and an
Assembly-sponsored public body responsible to the National Assembly for Wales. The EA was established to bring together previously disparate responsibilities for protecting the environment and to contribute to sustainable development.
The EA plays a central role in delivering the environmental priorities of Central Government and the Welsh Assembly Government through its functions and roles. This integrated approach means all elements of the environment are considered when any works are planned. It allows the EA to identify the best environmental options and solutions, taking into account the different impacts on water, land and air. The responsibilities include, for example, co-ordinating plans for whole river basins for water and land quality.
More specifically, the Environment Agency is responsible for determining the acceptability of discharges associated with the treatment of waste water (including storm sewage) and will set environmentally–protective conditions to any permits granted by them.
3.3.4 Consumer Council for Water (CCW)
The Consumer Council for Water (CCW) is a non-departmental public body established under the Water Act 2003 to represent consumers of water and sewerage services in England and Wales. The CCW is a national body with an English regional and Welsh structure to reflect the significant geographic variations in water and sewerage provision, and to keep in touch with consumers in their local communities.
The CCW functions and duties include the following:
having regard to the interests of all consumers of water and sewerage services in England
and Wales
obtaining and keeping under review information about consumer matters and the views of
consumers on such matters
making proposals, providing advice and information and representing the views of
consumers to public authorities, water and sewerage companies and others.
3.4 Urban Waste Water Treatment Directive and related UK Regulations
3.4.1 The Urban Waste Water Treatment Directive
The Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors (Article 1). It is made clear in Article 1 that “The objective of the Directive is to protect the environment from the adverse effects of the above mentioned waste water discharges”.
Article 2 sets out the definitions of various terms. The term ‘urban waste water’ is defined to mean ‘domestic waste water or a mixture of domestic waste water with industrial waste and/or runoff rain water’; a ‘collecting system’ means ‘a system of conduits which collects and conducts urban waste water’ and ‘secondary treatment’ means ‘treatment of urban waste water by a process generally involving biological treatment with a secondary settlement or other process in which the
requirements established in Table 1 of Annex 1 are respected’.
Article 3(1) provides that: “Member States shall ensure that all agglomerations are provided with collecting systems for urban waste water”. For an agglomeration over 15,000 such a system is to be in place by 31 December 2000, although the earlier date of 31 December 1998 applies where the discharge is into ‘sensitive areas’ as so defined.
Article 3(2) makes it clear that ‘collecting systems’ described in Article 3(1) have to satisfy the requirements of Annex 1(A) to the Directive. Annex 1(A) provides that:
The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding
volume and characteristics of urban waste water,
prevention of leaks,
limitation of pollution of receiving waters due to storm water overflows”.
The footnote to Annex 1(A) provides as follows:
“Given that it is not possible in practice to construct collecting systems and treatment plants in a way such that all waste water can be treated during situations such as unusually heavy rainfall, Member States shall decide on measures to limit pollution from storm water
overflows. Such measures could be based on dilution rates or capacity in relation to dry weather flow, or could specify a certain acceptable number of overflows per year.” Article 4(1) provides that:
“Member States shall ensure that urban waste water entering collecting systems shall before discharge be subject to secondary treatment or an equivalent treatment …”
This is to be achieved by the dates specified, depending on the size of the agglomeration. Article 4(3) then relates this to the requirements of Annex 1 as follows:
“Discharges from urban waste water treatment plants described in paragraphs 1 and 2 shall satisfy the relevant requirements of section B of Annex 1I.”
The requirements of Annex 1(B) include that:
“2. Discharges from urban waste water treatment plants subject to treatment in accordance with Articles 4 and 5 shall meet the requirements shown in Table 1.”
Table 1 sets out certain technical requirements for discharges from waste water treatment plants. Annex 1(B) paragraph 3 makes provision for discharges to ‘sensitive areas’ by reference to Table 2.
Article 10 of the Directive states that:
“Member States shall ensure that the urban waste water treatment plants built to comply with the requirements of Articles 4, 5, 6, and 7 are designed, constructed, operated and
maintained to ensure sufficient performance under all normal local climatic conditions. When designing the plants, seasonal variations of the load shall be taken into account.”
3.4.2 The Urban Waste Water Treatment Regulations
The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI 1994/2841) transpose the UWWTD into UK law.
Regulation 2 gives many of the same (or very similar) definitions as were found in the UWWTD including those for ‘urban waste water’, collecting systems’ and ‘secondary treatment’.
Regulation 4 sets out the duty to provide and maintain collecting systems and treatment plants. This is stated to ‘supplement’ the duties on sewerage undertakers under Section 94 of the Water Industry Act 1991.
Regulation 4(2) provides that the duty imposed by subsection (1)(a) of Section 94 shall include a duty to ensure that collecting systems are provided which satisfy Schedule 2 of the regulations. Schedule 2 provides that:
“Collecting systems shall take into account waste water treatment requirements. The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding
prevention of leaks,
limitation of pollution of receiving waters due to storm water overflows.”
These are the same requirements as imposed under Annex 1(A) of the Directive.
Regulation 4(3) provides that the duty imposed by subsection (1)(a) of Section 94 shall include a duty to ensure that urban waste water entering collecting systems is, before discharge, subject to treatment in accordance with Regulation 5. Regulation 5 imposes time limits for the provision of treatment plants which provide secondary treatment and Regulation 6 and Schedule 3 then impose technical requirements on the standard of discharge, etc. These requirements are in essence the same as those in Annex 1(B) and Tables 1 and 2 to the Directive.
3.5 Statutory duties of the water and sewerage undertakers
The water and sewerage undertakers are also subject to various statutory duties under domestic legislation. This section draws particular attention to those duties contained in the Water Industry Act 1991 (WIA) and the Water Resources Act 1991 (WRA).
3.5.1 Water Industry Act 1991 (WIA)
Section 94 (1) of the WIA provides that:
“It shall be the duty of every sewerage undertaker -
(a) to provide, improve and extend such a system of public sewers (whether inside its
area or elsewhere) and so to cleanse and maintain those sewers as to ensure that that area is and continues to be effectually drained; and
(b) to make provision for the emptying of those sewers and such further provision
(whether inside its area or elsewhere) as is necessary from time to time for effectually dealing, by means of sewage disposal works or otherwise, with the contents of those sewers.”
Thus a sewerage undertaker has a duty to provide public sewers to ‘effectually’ drain its area and to make provision for the emptying of those sewers and ‘effectually’ dealing with the contents of those sewers. This duty is now supplemented by the requirements of Regulation 4 of the UWWTR. Section 94(3) of the WIA provides that the duties of a sewerage undertaker under section 94(1) shall be enforceable under section18 by the Secretary of State or, in certain circumstances, by the Chairman or Chief Executive of Ofwat. Section 18 provides for the making of an ‘enforcement notice’ where there is contravention of any statutory or other requirement enforceable under the
section.
3.5.2 Water Resources Act 1991 (WRA)
Section 85 of the WRA creates the offence of pollution of controlled waters. In particular, section 85(3) provides that:
“A person contravenes this section if he causes or knowingly permits any trade effluent or sewage effluent to be discharged
(a) into any controlled waters”
The tidal Thames is a ‘controlled water’ for the purposes of section 85.
Section 88(1), however, provides that a person shall not be guilty of an offence under section 85 in respect of any discharge, if that discharge is made under and in accordance with “(a) a consent given under this Chapter …”. Section 88(2) gives effect to Schedule 10 to the WRA with respect to the making of applications for consent for the purposes of section 88(1)(a). Schedule 10 sets out the procedural requirements under the WRA relating to the grant of ‘discharge consent’ by the Environment Agency.
Regulation 6(2)(c) of the Urban Waste Water Treatment Regulations requires the Environment Agency, in exercising its functions under Chapter II of Part II of the WRA (which includes sections
85 and 88), to “secure” the “limitation of pollution of receiving waters due to storm water overflows” with respect to any discharge from a collecting system described in regulation 4 (see above).
3.6 The Water Framework Directive and associated requirements
3.6.1 The Water Framework Directive
The Water Framework Directive (WFD) (2000/60/EC) establishes a framework for community action in the field of water policy. The Preamble sets out the objectives, including:
“This Directive aims at maintaining and improving the aquatic environment in the Community.” (Paragraph 19);
“Member States should aim to achieve the objective of at least good water status by defining and implementing the necessary measures within integrated programmes of measures, taking into account existing Community requirements. Where good water already exists it should be maintained.” (Paragraph 26); and “Member States should adopt measures to eliminate pollution of surface water by priority substances and progressively to reduce pollution by other substances which would otherwise prevent Member States from achieving the objectives for the bodies of surface water.” (Paragraph 45).
Its stated purposes in Article 1 include the establishment of a framework for the ‘protection’ of inland surface waters which “prevents further deterioration and protects and enhances the status of aquatic ecosystems” and “aims at enhanced protection and improvement of the aquatic
environment, inter alia, through specific measures for the progressive reduction of discharges …” . Article 2 sets out various definitions including ‘environmental objectives’ which means the
objectives in Article 4. Article 2 also defines the terms ‘river basin’ and river basin district’. A ‘heavily modified water body’ means “a body of surface water which as a result of physical alterations by human activity is substantially changed in character, as designated by the Member State in accordance with the provisions of Annex II”. The Thames Tideway has been designated as a candidate ‘heavily modified water body’ (HMWB) due to flood defence and ports/navigation uses. The term, ‘good surface water status’, is defined as meaning “the status achieved by a surface water body when both its ecological status and its chemical status are at least ‘good’”. The term ‘good ecological potential’ is “the status of a heavily modified body of water, so classified in accordance with the provisions of Annex V” and ‘good surface water chemical status’ means “the chemical status required to meet the environmental objectives for surface waters established in Article 4(1)(a), that is the chemical status achieved by a body of surface water in which
concentrations of pollutants do not exceed the environmental quality standards established in Annex IX and under Article 16(7), and under other relevant Community legislation setting environmental quality standards at Community level.”
Article 4 sets out ‘environmental objectives’ and provides (Article 4(1)) that
“in making operational the programmes of measures specified in the river basin management plans for ‘surface waters’ Member States shall:
(i) … implement the necessary measures to prevent deterioration of the status of all bodies of surface water …
(ii) … protect, enhance and restore all bodies of surface water, subject to the application of subparagraph (iii) for …heavily modified bodies of water, with the aim of achieving good surface water status at the latest 15 years after the date of entry into force of this Directive [2000], …
(iii) … protect and enhance all …heavily modified bodies of water, with the aim of achieving good ecological potential and good surface water chemical status at the latest 15 years from the date of entry into force of this Directive [2000], in accordance with the provisions laid down in Annex V…”
Article 4 (4) allows the deadline for compliance to be extended, subject to various conditions Article 4(5) allows the adoption of less stringent environmental objectives, where achievement would be infeasible or disproportionately expensive, subject to conditions
Article 5 sets out various duties imposed on Member States in relation to analysis of the characteristics of river basin districts, review of the impact of human activity on the status of surface waters and economic analysis of water use.
Article 11(1) provides that: “Each Member State shall ensure the establishment for each river basin district … of a programme of measures, taking account of the analysis required under Article 5, in order to achieve the objectives established under Article 4. …”
Such measures are to include ‘basic’ measures and, where necessary, ‘supplementary’ measures. These are set out in Article 11 and Annex VI. (Note: Basic measures include full implementation of existing directives such as the UWWTD).
Article 2 (18) defines ‘Good surface water status’ as the status achieved by the body of surface water when both its ecological and chemical status are at least ‘good’. Article 2(22) and Annex V, Table 1.2 give the normative definition of good status as where “the values of the biological quality elements for the surface water type show low levels of distortion resulting from human activity but deviate only slightly from those normally associated with the surface water body type under undisturbed conditions.” Article 2(24) defines ‘Good surface water chemical status’ as that required to achieve the objectives in Article 4(1)(a) as set out above by not exceeding the standards in Annex IX and under Article 16(7).
Article 13(1) provides that “Member States shall ensure that a river basin management plan is produced for each river basin district lying entirely within their territory.” A river basin management plan has to include the information detailed in Annex VII (Article VII). This annex sets out the detailed requirements for the production of river basin management plans.
3.6.2 Water Framework Directive Regulations
The WFD was transposed into UK law by the Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 (SI 2003/3242).
3.6.3 Implementation of the WFD
In England and Wales the Environment Agency is the competent authority to implement the WFD. The key objectives of the WFD are summarised as follows:
prevent deterioration in the classification status of aquatic ecosystems, protect them and
improve the ecological condition of waters
aim to achieve at least good status for all waters by 2015. Where this is not possible, good
status should be achieved by 2021 or 2027
promote sustainable use of water as a natural resource
conserve habitats and species that depend directly on water
progressively reduce or phase out releases of individual pollutants or groups of pollutants
that present a significant threat to the aquatic environment
progressively reduce the pollution of groundwater and prevent or limit the entry of pollutants
contribute to mitigating the effects of floods and droughts.
3.6.3.1 No deterioration
The first principle of the WFD is to prevent deterioration in aquatic ecosystems. ‘No deterioration’ must be met in all but very exceptional circumstances. Exceptional circumstances apply when the deterioration is caused by physical modifications or is the result of sustainable new human
development activities. Even in such cases, it is necessary to demonstrate that there was no better way to achieve the desired development. ‘No deterioration’ requires that a water body does not deteriorate from its current ecological or chemical classification, and is assessed on the quality achieved by individual pollutants within a water body. For example, if dissolved oxygen was currently classified as meeting the standards for moderate status, then the first principle of the WFD would be to ensure no deterioration from the moderate class.
3.6.3.2 Good status
Under the WFD the objective is for all water bodies to meet good ecological status by 2015. For surface waters (rivers, lakes, transitional waters), good ecological status can be defined as:
good chemical status for the relevant substances (with a series of daughter directives)
good physico-chemical status on the scale high, good, moderate, poor and bad
good biological class
good hydro-morphological class.
The status of a water body is measured through a series of specific standards and targets that have been developed by the UK administrations, supported by the WFD UK Technical Advisory Group (www.wfduk.org). This includes standards and targets for surface water, transitional waters, coastal waters, and lakes.
The manner in which overall status is assessed is by using a ‘one out, all out’ approach. That is, the status is determined by the lowest common denominator. As an illustration, if ammonia was classified as satisfying the standards for ‘high’ status but dissolved oxygen was classified as ‘moderate’, then the water body would be considered to be in the ‘moderate’ class.
3.6.3.3 Alternative objective
Although the WFD specifies that good status should be met by 2015, there are circumstances where it is possible to delay meeting good status until 2021 or 2027, or where a lesser objective will be required. These circumstances include technical feasibility of the required measures, disproportionate costs or natural conditions (recovery times). For the first river basin plans an extended deadline (i.e., 2021 or 2027) to meet good status has been adopted, rather than setting a less stringent objective.
Under Article 4 (3) of the WFD, it is possible to designate water bodies as artificial or heavily modified water bodies. The WFD recognises that some water bodies have been modified to provide valuable social or economic benefits, and it is recognised these water bodies are not able to achieve natural conditions, and hence should not be required to achieve good ecological status. Artificial or heavily modified water bodies therefore have an alternative objective of meeting ‘good ecological potential’ and these are identified in the River Basin Management Plans. It should be noted that the chemical standards to meet ‘good ecological potential’ for artificial or heavily
modified water bodies are identical to the chemical standards to meet ‘good ecological status’. It is the hydro morphological requirements of a water body which differ depending on the designation of a water body.
3.6.3.4 River Basin Management Plans (RBMP)
As part of their implementation role in England and Wales, the Environment Agency has prepared
River Basin Management Plans (RBMP)2, which set out:
the current status for each water body (including confidence limits)
the objectives and targets for each water body
the main pressures for each water body
an action plan outlining what will be required, by whom, and when to meet good ecological
status (or potential).
justification for setting an alternative objective by 2015.
The first RBMPs were adopted in December 2009, and will be reviewed and updated every six years (i.e., 2021, 2027).
2 Further information on RBMP can be found at www.environment-agency.gov.uk//planning/
3.7 Powers of the European Commission to bring infraction proceedings
Article 258 of the Treaty of Lisbon gives the European Commission powers to take legal action against a member state that it considers is not respecting its obligations under EU Directives. The first stage is the issue of a Reasoned Opinion which serves as a formal warning. The next step in the Article 258 proceedings is for the Commission to refer the matter to the European Court of Justice seeking a judgement that the member state concerned has failed to meet its obligations. Were the court to make such a ruling, the Commission could then bring proceedings under Article 260 seeking fines (a lump sum and periodic penalty payments) due to a failure to take the
necessary steps to comply with the judgement. Periodic penalty payments would continue to be due until the judgement had been fully complied with.
4 THE NEED
The objective of the EU Urban Waste Water Treatment Directive relates to the
protection of the environment from the adverse effects of insufficiently treated waste water discharges.
Waste water collecting systems in London, in the opinion of the European
Commission, are being allowed to spill untreated waste waters from combined sewer overflows too frequently and in excessive quantities.
The Directive, and related UK legislation, accepts that collecting systems and
treatment plants may spill water in certain situations, such as unusually heavy rainfall, but the Commission considers that spills in the case of London are excessive and go beyond what the legislation provides for.
Infraction proceedings are being pursued by the European Commission against the
UK for breach of the UWWTD. On 8 October 2009 the European Commission announced its decision to take the UK to the European Court of Justice because it considers that the waste water collection systems in London are being allowed to spill untreated waste water from CSOs too frequently and in excessive quantities.
London’s sewerage system (the Beckton and Crossness sewer catchments) has been
progressively extended to accommodate development and population growth since it was designed by Sir Joseph Bazalgette in the 1850s. Despite this, there is now little spare capacity in the sewerage network.
Currently, spillages to the Thames Tideway occur more than 50 times per year at the
most frequently overflowing CSOs. An estimated total of some 39 million cubic metres of storm sewage enter the river from the Beckton and Crossness sewerage catchments in a typical year.
Waste water discharges affect the environment in three main ways, which have been
considered in developing the specific objectives for the project, namely by:
o adverse environmental impacts on the river ecosystems and on fish species in
particular;
o unacceptable aesthetic issues; and
o elevated health risks for recreational users of the Thames.
The then Minister of State for Climate Change & Environment wrote to Thames Water
on 17th April 2007: “a full-length storage tunnel with additional secondary treatment
at Beckton sewage treatment works – is needed …… for the UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water
overflows.” The succeeding Environment Secretary, Caroline Spelman, issued a written
ministerial statement on 07 September 2010 confirming the coalition government’s support for the construction of the tunnel from Hammersmith to Beckton.
As defined by the EA, there are 34 unsatisfactory CSOs in the Beckton and Crossness
catchments discharging directly into the River Thames. Modelling has indicated that, after construction of the Lee Tunnel and the extensions to the STWs at Beckton and Crossness, in a typical year 18 million cubic metres of storm sewage will enter the river from these CSOs.
The River Basin Management Plan for the River Thames (December 2009) states that
in the Estuaries and Coastal Waters Catchment, the London Tideway Tunnels (the Thames and Lee Tunnels); “represent the primary measures to address point source pollution from the sewer system and are fundamental to the achievement of good status in this catchment”
Thames Water is progressing improvement projects, including the construction of the
Lee Tunnel and the upgrades to the STWs at Mogden, Beckton, Crossness, Riverside and Long Reach. The provision of a full-length storage tunnel under the river (the Thames Tunnel), as required by Government, will be the final step in reaching compliance with European legislation.
4.1 London’s sewerage
4.1.1 Introduction
The Thames Tunnel catchment comprises the catchments served by the Beckton and Crossness STWs as illustrated in Figure 4.1. The Beckton and Crossness catchments are combined sewer systems (foul sewage and storm water runoff) whilst the Mogden catchment to the west is predominantly served by separate sewage and rainfall systems. Sewer capacity is currently sufficient for dry weather flows but it is normal practice for discharges to water courses via sewer overflows during rainfall events to avoid the sewers backing up and causing flooding. The location of the overflows in the Beckton and Crossness catchments are shown below in Figure 4.2.
Figure 4.1 Catchment areas draining to Mogden, Beckton and Crossness STWs
Over the years, urbanisation (the reduction in permeable areas in the catchment leading to increases in the flows and flow rates in the sewers) has increased the quantity of storm sewage and, as a consequence increased the frequency and volume of combined sewage discharged to the river. Currently, some CSOs spill more than 50 times per year, with a number activated by rainfall of only a few millimetres.
4.1.2 General characteristics of the catchments
The Thames Tunnel sewer catchment consists of the area north of the River Thames (Beckton catchment) that drains to the Beckton STW, and the South London area (Crossness catchment)
that drains to the Crossness STW. The catchments cover an area of about 326km2 in the north
and 230km2 in the south, stretching approximately 25km north to south and approximately 30km
west to east. Ground levels fall towards the River Thames in the direction from west to east – hence the location of Beckton and Crossness in the east of the catchment (although waste water disposal at outgoing tides was also a consideration in works’ location). The River Thames has meandered through the valley over time but today is generally confined by river walls and other flood defences.
The Thames Tunnel sewer catchment includes all or part of the London Boroughs, north of the River Thames, of Barking, Brent, Camden, the City of London, Ealing, Hackney, Hammersmith & Fulham, Haringey, Islington, Kensington & Chelsea, Newham, Redbridge, Tower Hamlets, Waltham, and Westminster, and, south of the river, the London Boroughs of Bexley, Bromley, Croydon, Greenwich, Lambeth, Lewisham, Merton, Southwark, Sutton and Wandsworth. In the north part of the area of Epping District Council also drains to the Beckton catchment.
Since sewerage was provided in the 19th century, London’s population has continued to grow and
expand. The peak in population total and density occurred in the 1930s to 1950s, with a steady decline following the Second World War into the late 1980s, after which saw an increase in the London population (population statistics are included in Appendix C). Population has therefore been steadily increasing since the 1990s, and the projection is for continued growth of the London population into 2021, when the Thames Tunnel is scheduled for completion, and beyond.
4.1.3 Description of a sewer system
London’s sewerage is fundamentally based on the London Main Drainage system constructed in the 19th century by the Victorian civil engineer, Sir Joseph Bazalgette. Many of the original tributary watercourses in London were incorporated into the sewer system, which means the massive volume of storm water runoff generated from the land area is drained to the combined sewer system.
Flows into the combined sewer system are made up of dry weather flow, comprising domestic effluent, trade discharges, groundwater infiltration, and storm water runoff from the catchment. The amount of each is defined by the land use in the area and the type of sewer system serving the area. The sewer system is fully combined in the older parts of London, i.e. the inner boroughs, whereas in the outer boroughs there is a mixture of partially or fully separated collection systems. Generally, the amount of storm flow separation is dependent on the age of the development in the borough.
The oldest parts of London are largely within the Beckton catchment, within which 53% of the area is served by a combined sewer system. The average impermeability of the land surface within the Beckton catchment is 54% with some sub-catchments almost fully impermeable. In comparison, 18% of the Crossness catchment is served by a combined system, with the remainder either partially or fully separated. The average impermeability is considerably lower, at 24%, which is indicative of the smaller area of combined sub-catchments and the slower development of the Crossness catchment historically.
4.1.4 Current level of service
The capacities allowed for in Bazalgette’s project have now been exceeded. Despite the numerous improvements and extensions over the years, there is little spare capacity in the sewer system. The existing collection system that normally conveys flow to Crossness and Beckton STWs has become progressively more overloaded as the population of London has increased. In addition, an
