Planning for Flood Risk Management in the

Technical Scoping Report

March 2003 Planning for Flood Risk Management in the Thames Estuary Technical Scoping Report

Environment Agency Rio House Waterside Drive Aztec West Almondsbury Bristol BS32 4UD

March 2003 Publishing organisation

Environment Agency Rio House Waterside Drive Aztec West Almondsbury Bristol BS32 4UD

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All rights reserved. No part of this document may be produced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the Environment Agency.

Statement of use This document provides information for use by the Environment Agency in scoping the Planning for Flood Risk Management in the Thames Estuary project.

Contract Statement This report presents the scoping exercise conducted by HR Wallingford for Planning for Flood Risk Management in the Thames Estuary. The Environment Agency, whose representative was Sarah Lavery, commissioned the study and the HR Wallingford Job Number was DAS 0806. Mervyn Littlewood and Matt Crossman prepared the report with key contributions from Paul Sayers, David Ramsbottom, Dr Richard Whitehouse, Dr Peter Hawkes, Dr Mike Dearnaley, Roy Atkins and Silvia Segura. The HR Wallingford responsible Director was Dr Jane Smallman.

Key members of client and project team

Prepared by ...... Mervyn Littlewood and Matt Crossman HR Wallingford, Project Managers

Approved by ...... Dr Jane Smallman HR Wallingford, Director

...... Sarah Lavery Environment Agency, Project Manager

HR Wallingford accepts no liability for the use by third parties of results or methods presented in this report.

The Company also stresses that various sections of this report rely on data supplied by or drawn from third party sources. HR Wallingford accepts no liability for loss or damage suffered by the client or third parties as a result of errors or inaccuracies in such third party data.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT - ii - EXECUTIVE SUMMARY

Large areas of the Thames Estuary are potentially at risk from tidal flooding and are currently protected to a high standard by the defences constructed in the late 1970s and early 1980s, which included the Thames Barrier at and raised defences eastwards to Southend-on- and the .

Most of these flood defences were designed to last until approximately 2030. The Environment Agency has recently started the process of planning their future strategy for managing flood risk in the Thames Estuary in order to ensure that it is in place before large-scale works are required. This report provides a context for the defences, it reviews available information and identifies key opportunities and constraints relating to the physical environment, existing management framework for the defences, assets at risk from flooding and appropriate boundaries for future studies.

Flood risk within the estuary is not simply dependent on the water level at sea (which itself results from a combination of factors), but influenced by a complex combination of meteorological factors, fluvial flows, estuary morphology and the operation of the flood defences. The area of influence extends to the whole of the Thames catchments and some distance into the

Due to the size and importance of the estuary the development of a flood risk strategy will clearly be a difficult undertaking, demanding a good understanding of a wide range of processes and issues including hydrodynamics, environmental, economic and social factors associated with flooding and potential schemes. Reliable decision-making within such a complex environment will require the development and application of a well-structured approach drawing on existing best practice and knowledge as well as the results of the latest research.. It will undoubtedly be necessary to adopt a tiered approach to decision-making, solving issues at a manageable local scale, but within a regional framework that recognises opportunities and constraints on an estuary wide scale.

The summary of hydraulic processes within the estuary identifies considerable gaps in information and understanding where further data will probably be required. One significant concern relates to the reliability of water level records and predictions. There is also only limited information available on the performance and condition of the existing defences and some uncertainty as to the accuracy of the indicative floodplain mapping published by the Environment Agency. This situation will be improved with the development of the National Flood and Coast Defence Database and completion of a number of studies in 2003. The initial assessment of assets at risk of flooding divided the indicative tidal floodplain between Teddington and Foulness Point / Whitstable into 43 flood risk compartments covering a total 468 km2 with capital values totalling more than £99,000 million.

Recommendations for the scope and timing of further studies are presented within ‘Advisory Report No. 1 in support of project development’ which has been prepared concurrently.

For further information regarding the information contained in this report please contact Paul Sayers or Jane Smallman at HR Wallingford.

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EXECUTIVE SUMMARY iii

1. Introduction 1

2. The Thames Estuary – A Context 2 2.1 Historical development of the Thames 3 2.2 Hydraulic drivers of flood risk 9 2.3 Hydraulic drivers and ecology 17 2.4 Overview of the defence system 18 2.5 Sediment processes and morphological response 20 2.6 Socio – economic constraints and opportunities 22 2.7 Recommendations 24

3. The Physical Environment 26 3.1 Hydraulic drivers 26 3.2 Sediment processes and morphology 36 3.3 The existing flood defence system 40 3.4 Environmental responses 43 3.5 Recommendations 43

4. Existing Management Framework 45 4.1 High level multi-disciplinary guidance 45 4.2 Flood and coastal defence policy and strategy 47 4.3 National and regional guidance and policy 50 4.4 Environmental, habitat and biodiversity 56 4.5 Recommendations 60

5. Identification of Assets at Risk from Flooding 62 5.1 Topography and ‘flood cells’ 62 5.2 Review of assets at risk from flooding 63 5.3 Future change scenarios 65 5.4 Definition of proposed valuation methodology for each asset type 66 5.5 Review of data for use in assessing economic impacts of flooding 66 5.6 Recommendations 69

6. Study Boundaries 70 6.1 Temporal 70

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT - v - CONTENTS CONTINUED

6.2 Management / intervention 71 6.3 Physical Processes / Understanding 72 6.4 Recommendations 72

7. Recommendations 74

8. References 77

Tables Table 2.1 Ranked extreme high waters at Bridge and 6 Table 2.2 Classification of flood defences by immediate hinterland 23 Table 3.1 Environment Agency water level data 27 Table 3.2 Authority water level data 27 Table 3.3 Tributaries and creeks discharging into the Thames Estuary 29 Table 3.4 Consented discharges into the Thames Estuary in 1995 29 Table 3.5 Consented discharges into tributaries in 1995 30 Table 3.6 Tidal current data 32 Table 3.7 ADP data sets 33 Table 3.8 Defence types comprising the Tidal Walls 40 Table 3.9 Approximate cost of existing tidal defences 41 Table 4.1 North Shoreline Management Policy 47 Table 4.2 South Shoreline Management Policy 48 Table 4.3 Indicative standards of protection (after MAFF 1999) 52 Table 4.4 Planning response to sequential characterisation of flood risk 54 Table 4.5 Summary of Water Level Management Plans 59 Table 5.1 Distribution of assets within the different flood risk compartments 63 Table 5.2 Proposed development within the Thames Gateway ‘Zones of Change’ 65

Figures Figure 2.1 Annual maxima levels at Sheerness 6 Figure 2.2 The 1953 surge 12 Figure 2.3 The 1953 and mean spring high water levels 13 Figure 3.1 An example of acoustic backscatter measurement of suspended solids concentration and other associated parameters 37

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT - vi - CONTENTS CONTINUED

Figure 4.1 Hierarchy of plans (after MAFF 2001b) 51

Drawings Drawing 01 Indicative flood risk areas in the Thames Estuary Drawing 02 Thames River basin Drawing 03 Geology Drawing 04 Tidal defence system Drawing 05 Environment Agency boundaries Drawing 06 Local authority boundaries Drawing 07 Population Drawing 08 Hydraulic measures locations Drawing 09 Discharges and outfalls Drawing 10 Wind and wave data Drawing 11 PLA chart extents Drawing 12 Environmental designations Drawing 13 Environmental resources Drawing 14 Archaeology Drawing 15 Extents of policy and strategy studies Drawing 16 Topography Drawing 17 Flood cells Drawing 18 Proposed development areas Drawing 19 Topographic data coverage Drawing 20 Relevant boundaries

Appendices Appendix A Planning for Flood Risk Management in the Thames Estuary 83 Appendix B The Outer Thames Estuary 97 Appendix C Combined Sewage Outfalls – Acton to Charlton 103 Appendix D Bathymetric information held at HR Wallingford 105 Appendix E Metadatabase listing 107

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ADP Acoustic Doppler Profiling

BGS British Geological Survey

BODC British Oceanographic Data Centre

CHaMP Coastal Habitat Management Plan

CEH Centre for Ecology and Hydrology

CFMP Catchment Flood Management Plan

CSO Combined Sewer Overflow

DEFRA Department for Environment, Food & Rural Affairs

DoE Department of Environment

EA Environment Agency

ESA Environmentally Sensitive Areas scheme

FCDPAG Flood and Coastal Defence Project Appraisal Guidance

FRCA Farming and Rural Conservation Agency

GLC Council

GLA

GIS Geographic Information Systems

GMT Mean Time

GPS Global Positioning System

HRW HR Wallingford Ltd.

IDB Internal Drainage Boards

IESSG Institute of Engineering Surveying and Space Geodesy

IFP Indicative Flood Plain

JBA Jeremy Benn Associates

LEAP Local Environment Agency Plan

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT - ix - MAFF Ministry of Agriculture, Fisheries and Food (now DEFRA)

MSEP and Swale Estuary Partnership

NFCDD National Flood and Coast Defence Database

ODN Ordnance Datum Newlyn

OD Ordnance Datum

ODPM Office of the Deputy Prime Minister

OS Ordnance Survey

PLA

POL Proudman Oceanographic Laboratory

PPG Planning Policy Guidance

RPG Regional Planning Guidance

RBD River Basin District

RSPB Royal Society for the Protection of Birds

SMP Shoreline Management Plan

SSSI Site of Special Scientific Interest

STW Sewage Treatment Works

TEP Thames Estuary Partnership

TGLP Thames Gateway London Partnership

TGSE - Thames Gateway Strategic Executive

TOSCA Thames Oil Spill Clearance Association

THAP Thames Habitat Action Plan

UKCIP United Kingdom Climate Impacts Programme

UKMO United Kingdom Meteorological Office

WFD Water Framework Directive WLMP Water Level Management Plan

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT - x - GLOSSARY

Catchment - the area of land bounded by watersheds draining into a river, basin, or reservoir.

Estuary – the widening channel of a river where it nears the sea, with a mixing of fresh and saline water.

Fluvial flooding – Refers to flooding by a process of overtopping or overflow of the river / estuary defences as a consequence of fluvial discharge.

Hard defence – steel, masonry, concrete or timber defences – usually vertical or steeply sloping

Indicative flood risk areas - areas of land in natural floodplains which are potentially at risk of flooding from rivers or the sea

Lower estuary - virtually open sea marine environment

Pluvial flooding –flooding by a process of urban run-off due to local rainfall.

Sluice –A structure, normally fitted with a gate, to control the rate of flow of water

Soft defence - earth embankments or similar defences providing a gradual gradient in habitat from land to water

Thames Estuary Flood Prevention Scheme - The tidal defences constructed in the late 1970s and early 1980s including the Thames Barrier at Woolwich, other barriers and floodgates and raising of the tidal walls to Southend and the Isle of Grain.

Tidal flooding – Refers to flooding by a process of overtopping or overflow of the river / estuary defences as a consequence of tidal influence.

Tidal waterway - an area where normal spring or neap tide flow occurs

Upper estuary – predominantly non-saline waters

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Indicative tidal and fluvial flood risk areas within the Thames Estuary are shown in Drawing 01 which illustrates the area (approximately 468 km2 between Teddington and Foulness Point / Whitstable) that would be liable to tidal flooding without the existing defences. Most of these defences were constructed or improved in the late 1970s and early 1980s as part of the Thames Estuary Flood Prevention Scheme. The defences were generally designed to last until about 2030 and the Environment Agency has recently started the process of planning their future strategy for managing flood risk in the Thames Estuary in order to ensure that it is in place before large-scale works are required.

Flood risk within the estuary is not simply dependent on the water level at sea, but influenced by a complex combination of meteorological factors, fluvial flow, estuary morphology and the operation of the flood defences. The area of influence extends to the whole of the Thames catchments and some distance into the North Sea. Due to the size and importance of the estuary the development of a flood risk strategy will clearly be a difficult undertaking, demanding a good understanding of a wide range of processes and issues including hydrodynamics, environmental, economic and social factors associated with flooding and potential schemes.

Reliable decision-making within such a complex environment will require the development and application of an innovative well-structured approach that draws upon existing best practice as well as the latest research and knowledge. Undoubtedly, however, it will be necessary to adopt a tiered approach to decision-making, solving issues at a manageable local scale, but within a regional framework that recognises opportunities and constraints on an estuary wide scale.

This report reviews the issues associated with flood defence within the estuary, describes the existing defences and provides an initial estimate of the assets presently defended against flooding. It identifies those issues that will need to be addressed through future studies and / or data collection and provides a discussion of the issues associated with the temporal and spatial boundaries for the flood risk management strategy which will be developed.

Further information on the proposed scope and timing of the studies and data collection is presented in ‘Advisory Report No. 1 in support of project development’ which has been prepared concurrently.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 1 2. THE THAMES ESTUARY – A CONTEXT

“Why was it necessary to build the Thames Barrier? Why were one million people living in an area that could be flooded to a considerable depth in a period of less than an hour, an area where so much investment in property, industry and infrastructure was liable to suffer serious temporary or permanent damage?” These questions were asked by Gilbert and Horner (Gilbert and Horner 1984), who provided part of the answer with the following:

The evolution of London as a major sea port resulted in the development of a considerable area of low-lying land close to the tidal for industrial and residential purposes. The long-term settlement of south-eastern England, combined with a steady rise in sea levels caused by the melting of the polar ice caps, led to a large area of land with a population of one million being at risk from a major flood disaster.

The main thrust behind the Thames Barrier and associated flood defence works was the need to protect London and its environs from tidal inundation during periods when the height of the predicted tidal waters of the estuary was increased by a .

Whilst this need is still of paramount importance and in itself undoubtedly justifies the existence of the present flood defence works, the Thames Barrier design concept and procedure operation studies were obviously completed using the information available at the time. There have been a number of changes since the construction of the works and additional information relating to issues such as operational experience and procedures; changing flood perception; changing riparian activities; modified catchment response, new studies relating to relative to the land, climate change, the environmental function of the estuary provide the information necessary to enable the present usage of the barrier to be reviewed and future flood defence needs and strategy to be examined.

The urgent need to protect London and the low-lying lands on either side of the estuary from the threat of tidal flooding was pursued with considerable single-mindedness. Environmental issues were certainly given much less consideration than is required today, but given the poor state of the estuary at the time it is not entirely surprising that this was the case. Neither is it surprising that the impacts of the flood defence works constructed as part of the overall flood defence measures on the rivers and creeks that feed off and into the tidal Thames waterway were not fully understood. Natural and anthropogenic evolutions, including commercial and environmental riverside schemes, which were not (with the benefit of hindsight) always adequately examined, have all had an effect on processes and water levels in the estuary and its tributaries.

Perceived tidal level rise relative to the land, whether as a consequence of sea-level rise or land settlement, possible increased storminess and climate change have and are being examined and will be discussed later. On occasion the findings of these studies have not always been reported in a manner that presents the whole picture, for instance it has been reported that maximum water levels in the estuary are rising by 800 mm per century. This can give the impression that the 800 mm applies to the whole of the estuary – it does not. Other studies deal with particular individual issues and consequently do not attempt to provide a holistic overview of the impact. The findings of the studies should not be used outside of the remit of the particular study without

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 2 appropriate use of other relevant data or acknowledgement of the potential impact of interactive issues that have not been included.

This review examines a range of studies, information and data that is representative of that available and details the data that will be required for the next phase of studies. It will be seen that the majority of the work to date has been associated with water levels, which is obviously one of the most important issues when considering flood risk. However, it does interact with and is interacted upon by other hydrodynamic, sediment and morphological issues and these as yet have not been adequately addressed. Much of the data reviewed is now more than twenty years old and in need of updating. Present day techniques allow more comprehensive data to be obtained than possible at the time of the Thames Barrier and associated studies. Using these new techniques provides a far better understanding of some of the parameters that can influence flood risk.

When considering flood risk within the estuary it is important to include the catchment areas that feed to and from the tidal Thames (these are fully described in Appendix A) and the Outer Thames Estuary to the east of the area covered in detail by this review (described in Appendix B).

2.1 Historical development of the Thames

2.1.1 Land use The land bordering the tidal Thames Estuary, large areas of which are below mean spring tide water level, has been progressively developed for commercial, residential, agricultural, social or recreational use over many centuries. These developments have, on occasion, occupied parts of either the principal tidal waterway (any area where normal spring or neap tide flow occurred) or areas on the margins of the tidal waterway (areas inundated by tidal surge or the combination of tidal water levels and high fluvial flow and referred to as the tidal flood plain). The flood risk significance of any particular development will be a function of the location, size and design of the scheme, in terms of its impact on the movement of tidal or fluvial waters in the upper tidal and lower, normally non-tidal reaches upriver of Teddington Weir.

Over the last fifty years the development of the catchments has resulted in major changes to the river system in order to provide improved land drainage, flood defence, navigation and also to reduce the space occupied by the river corridors for development purposes. This has this changed the character of parts of the river systems and affected the run-off response, which has required or could require modification to the flood defence strategy of each catchment. The continuing development of London, particularly to the east, will further affect catchment run-off and the standard of defence appropriate for these areas.

2.1.2 River use and riparian activity Since pre-roman times the Thames Estuary has been used for almost any activity that could be associated with a tidal estuary. The range of activities and usage has constantly changed in response to the requirements of the time and this evolution will obviously continue. The design and location of the Thames Barrier took into consideration the contemporary usage of the Thames, particularly the demands of shipping using the London Docks and the multitude of riverside facilities that existed.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 3 Use of the tidal estuary is extremely diverse for many reasons. The tidal estuary can be subdivided into several separate but hydrodynamically interdependent zones ranging from the non-saline waters in the protected upper reaches to the virtually open sea marine environment that exists in the lower estuary. In the upper estuary and increasingly so in the middle estuary above the barrier, the river and its frontage no longer supports a large volume of commercial activity.

Shipping The choice of location for the Thames Barrier took into consideration the needs of the commercial river traffic and especially safe access to and from the extensive dock and riverside facilities that existed between and the entrance to King George V dock in Gallions Reach. The rapid expansion of containerised cargoes between the design and official opening of the barrier meant that by the time the barrier became operational such consideration was no longer of such importance. The present trend is for regular large vessel operations to move progressively seaward to take advantage of shorter sailing time and generally deeper water, so effectively increasing the operational window available on each tide for the safe passage of sea-going vessels. Anticipating future use of the river for commercial shipping will not be an easy task. The advice of the Port of London Authority and operators will be of paramount importance to assess the potential future needs, as for example, the present navigation requirements may change in the coming years. In 2000 and 2001, excluding movements within the Thames Estuary there were over 26,000 vessel arrivals and departures to and from the Port of London carrying over 50 million tonnes of cargo, Unitised traffic totalled over 1,450,000 TEU (PLA 2002)

Sewage In the past domestic and commercial discharges into the tidal Thames were unrestricted. Legislation has meant that the discharge of untreated domestic sewage or polluted industrial effluent into the tidal Thames, except in unforeseen or exceptional circumstances has been eliminated. Storm water outfalls, remain a potential source of runoff pollution. In the event of storm water discharge from the CSOs being coincidental with Barrier closure, this could cause a serious deterioration to the quality of the tide-locked waters. For the purpose of the Thames Flood Risk Management studies it will also be of considerable importance to understand the potential total discharge from these discharges and hence the volume loss to upriver storage capacity from this source when the Barrier is closed.

Recreation The tidal Thames has provided many recreational opportunities and functions over the centuries. Presently, almost all types of non-immersion water related activity can be found somewhere within the wide-ranging conditions to be found within the tidal Thames Estuary. The type of recreational activity found in any particular stretch of the tidal Thames is a function of the local estuary regime. At the upstream end of the tidal Thames Estuary the waters are normally fresh and despite being fairly fast flowing during periods of the tidal cycle, mostly calm and not frequented by commercial vessels other than the occasional passenger carrying pleasure craft. At the seaward end in the vicinity of Southend the waters are saline, infrequently calm and subject to frequent passage of large commercial vessels.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 4 Since about the time the decision was made to proceed with the design studies for the Thames Barrier, although in no way connected, the ecosystem of the Thames Estuary has been recovering at a rate that would not have been anticipated to be possible at that time. There are many reasons for the recovery, which is continuing and increasingly becoming part of the natural evolution of the estuary. Although public perception of the estuary is that it is generally unsafe and unsuitable for recreational uses (TEP 1999) a wide and increasing range of recreational activity takes place in and around the estuary. This includes water and land based activities examples of which may be divided as follows:

S river channel: sailing, power-boating and rowing S water margins: angling, canoeing, swimming and wild-fowling S banks and marshes: walking, cycling, horse riding, heritage interests and bird watching S open spaces: orienteering, motor sports, clay pigeon shooting

Comprehensive details of recreational activities were described in the Thames Estuary Recreation Study published by the Thames Estuary Partnership in May 2001.

2.1.3 Defences The lands occupying much of the low-lying margins of the Thames Estuary have been subject to inundation from coupled with a surge component for hundreds of years. Gilbert and Horner (Gilbert and Horner 1984) refer to Stow’s record in his “Chronicles of England”.

In the year 1236 the River Thames, overflowing banks, caused the marshes all about Woolwich to be all at sea wherein boats and other vessels were carried by the stream, so that besides cattle a great number of inhabitants there were drowned, and in the great men did row with wherries in the midst of the Hall. Moreover in the year 1242, the Thames, overflowing the banks about Lamberhithe, drowned houses and fields by the space of six miles, so that the Great Hall at Westminster took to their horses, because the water ran overall.

The 1236 flood was probably linked to a storm in the North Sea, as Matthew Paris chronicles a major two day storm starting on 12 November 1236. It has not been established by this review as to whether the 1242 flood was as a consequence of tidal inundation, fluvial flooding or an in-combination event. Other significant high water events at include an event in 1663 when Pepys recorded “ being drowned in 1663”

Figure 2.1 shows the actual and detrended annual maxima high water levels at Sheerness for most years between 1819 and 1999 as reported by Jeremy Benn Associates (JBA 2000).

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 5 5

4.5

4

3.5 Elevation (m ODN)

3

2.5 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 Year

Recorded level Detrended level (1.75 mm / year)

Figure 2.1 Annual maxima tide levels at Sheerness

Tables of the information presented by JBA (JBA 2000) included a ranking for each of the high waters by level. Table 2.1 lists the tides associated with the significant events at London Bridge identified by Gilbert and Horner (it has been assumed that the highest of the year at Sheerness, was coincident with the London Bridge high level) and others post 1953.

The 1928, 1953, 1965 and 1978 high waters had a large surge component but many of the others may fall into the in-combination classification, that is a combination of a high tide and high fluvial flow and is particularly applicable pre 1928.

Table 2.1 Ranked extreme high waters at London Bridge and Sheerness

Year Event ranking at Event Ranking at London Bridge Sheerness (Gilbert and Horner) 1834 7 32 1852 6 87 1874 5 77 1875 4 56 1881 3 126 1928 2 5 1953 1 1 1965 6 1978 2 1996 7

Historically rising sea level, anthropogenic activity and development have resulted in the estuary becoming more tidal, especially in the middle and upper reaches. The

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 6 combination of these influences, the pressure for collective protection and the opportunistic enclosure of ‘land’ has effectively canalised the river between man-made banks. Most low-lying land at the margins of the estuary is now protected to a very high standard (see Section 3.3.1) with only limited stretches being naturally protected by high ground at the margins. Whilst some of the tidal creeks have been dammed, with discharges via sluices or outfalls in to the Thames proper, some of the tidal creeks have a combination of tidal walls capable of withstanding routine events and barriers may provide protection against extreme events.

2.1.4 Banklines The mean high water spring tide bankline on either side of the tidal Thames and its tributaries and creeks is virtually on the same alignment as the flood defence line at the majority of locations. At a limited number of locations the defence line presently lies behind the bankline. There are exceptions and these are mostly to be found downstream of the Barrier especially in areas where saltings or saltmarsh fronts the flood defence works – for example at Higham, Mucking and East Canvey.

2.1.5 Changes to fluvial flows Long-term The Thames Estuary sits at the seaward end of the Thames catchment area and consequently receives fluvial flow from the variety of sources within that catchment. These are described in Chapter 3.1.2. The primary impact of river catchments on flood risk in the tidal Thames is the amount of water that can enter the reach upstream of the Thames Barrier and the effect this has on flood levels and the operation of the Barrier.

By far the largest inflow into the tidal Thames is from the Thames upstream of Teddington. The flow record dates back to 1883 and the highest flow on the record was estimated to be 1,059 m3/s in 1894. There has been a trend over the last 50 years of reduced frequency and magnitude of flood events on the non-tidal Thames (Crooks 1994). Another major fluvial event occurred in 1947, when the flow at Teddington was estimated to be 714 m3/s. Flood hydrographs on the Thames can last for several days (for examples, see Dunsmore 1997) and in January 2003 the fluvial flows over a period in excess of one week were sufficient to cause serious flooding in many sections of the Thames catchment. At the time of writing details are unconfirmed but it is understood that 1947 water levels were approached or in some cases exceeded. Uncalibrated flow data from Kingston (Teddington) suggests that the fluvial flow peaked on 2 January 2003 when the flow averaged 460.7m3/s. The levels and discharges alone clearly do not tell the whole story. Why is there so much variation between the 1947 and 2003 fluvial discharge if the levels were similar? Accuracy of measurement or the management of levels/ discharges within the catchment are two areas that require further examination.

Changes to the long-term mean daily flow or the frequency of various fluvial flow events will affect, amongst other parameters, the salinity and sediment regimes. Actual or projected changes to catchment criteria and/or abstraction policy, both of which have significantly changed since the Thames Barrier studies, will therefore need to be examined.

Land drainage and flow routing The discharge of land drainage into the tidal Thames and many of its creeks and tributaries has over the years played an important role in creating the hydrodynamic,

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 7 sediment and environmental regimes and the sustainability of some of these systems that discharge into the tidal Thames. Understanding the impact of changes to these discharges either in quantity, frequency or re-routing as a consequence of flood defence works or otherwise will require attention if the environmental function of an individual creek is to be sustained. If change is introduced to any of the forces that presently sustain the individual system there will be an especially locally, for example, flow routing of even small flows could have a significant impact in tidal creeks.

Control and defence infrastructure Flood defence infrastructure in the River Thames catchment upstream of Teddington consists of the following:

S Control gates and control structures on the Thames and some tributaries, which can be opened to allow the passage of floodwater. S Enlargement of river channels by widening and dredging to improve flood capacity, and associated maintenance of these works. S “Engineered” river channels on some tributaries of the Thames which increase the flood capacity of watercourses, particularly those that pass through urban areas. S Construction of local flood alleviation measures and other engineering works, for example the Windsor, Eton and Maidenhead flood diversion channel on the Thames and the Lower Colne flood alleviation scheme which includes the Staines bypass channel and numerous other works.

Flood defence infrastructure on other rivers that drain directly into the tidal Thames includes the following:

S Enlarged and / or ‘engineered’ river channels which increase the flood capacity of watercourses, particularly those which pass through urban areas. These include numerous culverts and other crossing structures. In some cases dredging and other maintenance work is needed to maintain the flood capacity. S Control gates at control structures, which can be opened to allow the passage of flood water. S Some tributaries have control gates at the confluence with the tidal Thames. These maintain the integrity of the tidal defences and prevent backflow of tidal water under the defences. In addition to the main tributaries, there are numerous smaller outfalls where backflow is prevented by flap gates. S Some of the tributaries with control gates at the confluence with the tidal Thames also have pumps to assist with the discharge of flood water during high tides, for example on the Wandle and drainage of the area. S Some tributaries have tidal defences in their lower reaches, either up to the control structure at the tidal limit (for example, on the Lee or the Crane), or up to a tidal flood defence barrier. S Other flood defence schemes, for example the Lower Lee flood diversion channel. S Tidal flood barriers on the Roding (Barking) and the Darent (Dartford). There are also three flood barriers in the vicinity of Canvey Island. There are concerns about

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 8 the Barking barrier, because of the impacts of upstream development, and the Dartford barrier, because of instability of the river site.

Embankments and walls for fluvial flood defence are not generally used in the Thames Region. The impact of the above flood defence works would be to change the characteristics of flood flows downstream, as follows:

S More ‘peaky’ flood hydrographs with higher peak flows. S More rapid movement of the flood wave, changing the timing of the flood hydrograph on individual tributaries and consequently combined hydrographs downstream of confluences.

Since the Thames Barrier and associated flood defence studies the management of fluvial flow and land drainage discharges into the tidal Thames has evolved, in some cases significantly, for a variety of reasons, including re-routing of land drainage discharge and increased abstraction for potable supply. An understanding of the changes will be essential to the Thames Flood Risk Management study. This issue and associated matters are discussed in Appendix A.

Catchment influence At present the flood defence system in some of the creeks and tributaries is based on a combination of flood defence walls and a barrier or control structure, the operation of which is often directly linked to the operation of the Thames Barrier. The operational rules for such structures were largely determined using the catchment properties at the time of the Thames Barrier studies and it will be important to assess whether they remain appropriate given changes in the catchment and impacts of barrier operation. This is particularly important in the case of the Roding catchment and the operation of the Barking Barrier.

2.1.6 Industrial abstraction and discharge Quantity and quality The quantity of water abstracted from and more often than not returned to the river for industrial purpose has reduced significantly since the Thames Barrier studies because of the changes to the type and quantity of riverside industrial uses. For example the demand for power station cooling water has reduced, especially upstream of the Barrier, because of the significant reduction in the number of power stations. Many other riverside industries that used to make use of river water (for example the brewing, tanning and printing industries) have now closed.

In the past many of these industrial discharges were at best only partially controlled, which allowed a range of non-indigenous temperature or solid elements to enter the river. The lack of appropriate data does not allow the impact of these changes to be well understood.

2.2 Hydraulic drivers of flood risk

2.2.1 Tides The primary driver of flood risk within the majority of the Thames Estuary is tidal water level when surcharged with a surge component. Any change to sea level relative to the land or greater tidal range increases the risk of tidal related flooding. Tidal predictions

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 9 are made assuming “average” meteorological conditions, thus any significant deviation from the “average” will alter predicted tidal levels, for example a reduction in barometric pressure of 10 mbars will cause sea levels to rise by approximately 0.1m. Surge formation is a more complicated process, and is normally associated with either a rapidly moving depression, which raises levels or a rapidly moving high pressure, which depresses levels.

Many studies have been conducted to determine potential trends in future tidal water levels in the Thames Estuary. These studies have used existing data and previously predicted data. For several decades it has been perceived that the south east of England is sinking relative to a sea level that is rising. The rate of rise of sea level relative to the land at Southend appears to be relatively stable being in the order of 1.22 M0.24 mm per year between 1933 and 1983 (IESSG and BGS 1999).

Further up the estuary the rate of sea level rise relative to the land is not so easy to determine as either the length of record is of shorter duration or because of the unknown influence of other factors. Between 1961 and 1983 sea level to land level rose by 1.58 M0.91 mm per year at Tilbury, whereas records suggest that the difference could be as much as 8 mm per year at London Bridge (Muir Wood 1990). It is unclear how representative of the actual change this is as ground movement, the accuracy of Ordnance Datum and the potential impact of other issues is unknown. A description of the issues relating to these changes is given by Muir Wood (Muir Wood 1990) and although not all of the information agrees with the above his reasoning and concerns remain largely applicable and in some cases are now even more relevant than they were at the time. The following are quotes from a section of Muir Wood’s paper:

Tide-gauges have been installed at a number of locations around the Thames estuary, although lacking any coherent programme of investigation they have been operated and removed at whim, frustrating researchers who require long periods of data from which to demonstrate secular trends….

In the likely event that eustatic sea-level rise will start to accelerate the inhabitants of London will look back at the scientists and politicians involved in the decisions of the 1970s with incredulity. No geodetics, no seismic reflection, no seismic monitoring; the city mist await new storm surges to discover how the subsidence is proceeding.

All tidal gauges recording water levels are levelled to Ordnance Datum and for many studies it has reasonably been assumed that Ordnance Datum is the same level throughout the estuary. This was the case when the benchmarks used to level in the gauges were last verified. It is believed that this last occurred at least forty years ago and given the uncertainty of ground settlement in the Thames Estuary more than sufficient time has passed to suggest that there could now be significant variation between perceived and actual datum levels of the gauges. This variation may not be a constant along the whole of the tidal Thames because of differential land movement.

Modern technology using GPS levelling (IESSG and BGS 1999) enables an assessment of the actual geode height of any particular position to be determined to a high degree of accuracy. The analysis of the GPS information (IESSG and BGS 1999) covers a period of 2.25 years between March 1997 and July 1999 and provides evidence to suggest that the belief that south east England is sinking may indeed not be the case. A meeting held

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 10 at IESSG Nottingham University in August 2002 discussed the findings and it was agreed that a proposal should be submitted to extend the analysis to include data recorded since July 1999, which would significantly increase the confidence level of the results. Ordnance Datum levels can presently be determined to an accuracy of about M10 mm. Advantage should be taken of this as soon as possible to clarify the level of each recording location relative to a consistent datum. This should be carried out as soon as possible and additional tide recording locations established within the tidal estuary. An assessment of the potential impact of Ocean and Earth Tides on tidal water levels should also be done to determine the through-tide variation at individual locations and from location to location at a given time.

It is essential that these suggested monitoring exercises are put into practice to achieve a good understanding of tidal propagation and levels within the tidal Thames estuary. Without this knowledge setting-up of even the most basic numerical model to examine the impact of the potential flood risk management schemes and environmental issues cannot be carried out with the required high degree of confidence.

2.2.2 Fluvial flows Tidal water levels in Thames are strongly influenced by fluvial flow especially in the reaches above Westminster. Water level in the non-tidal catchments or in the areas where catchment and tidal flows occasionally interact is largely dictated by the fluvial flow.

Inflows from the catchments draining into the tidal Thames can contribute to flooding on the tidal Thames when high fluvial flows combine with high tides with no surge component, particularly in the Upper Estuary where the influence of the fluvial flow on tidal water level is greatest.

By closing the Thames Barrier during the previous low tide, the impact of flooding caused in this way can be reduced. The Barrier closure provides a reservoir upstream to contain the fluvial inflow and it is therefore important to understand how fluvial flows will change in the future to assess the impact on flood risk from this source.

It is important that the impact of the fluvial flow on tidal water levels is understood as any fundamental change will potentially affect other parameters (salinity, morphology for example), which in turn can impact on tidal propagation and hence water levels.

The UK Climate Impacts Programme 2002 study (Environment Agency 2002a) suggests that an increase of 20% to river and urban drainage flows should be considered as an appropriate precautionary allowance for conditions in 2080. This projection will have to be incorporated into the studies and it is suggested that other values be examined to determine the sensitivity of the Thames Estuary and its catchments to fluvial flow.

In areas, where for example, possible change to the fluvial discharge may be affected by modified catchment characteristics the impacts will also require assessment.

Since writing the main body of this report a major fluvial event occurred at the end of 2002 and the beginning of 2003 (see Section 2.1.5). Because this period of high fluvial flow coincided with large spring tides the Thames Barrier was operated on fourteen

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 11 consecutive tides during the first week of 2003. On all occasions barrier closure was carried out around mid flood tide and not at low water as stated above. Time has not permitted detailed assessment of the impact of these closures on water level and the river regime in general. However, initial examination of tidal records provides evidence to suggest that the reflected wave generated by such closures could have raised high water level elsewhere in the estuary by about 0.5 m. None of the closures were associated with a surge tide.

2.2.3 Surges and in-combination events Events referred to as surge tides are a combination of the astronomical predicted tide and a surge component. A surge tide at the seaward end of the Estuary can be described as any occasion when the actual tide is different to the predicted tide. The difference can be positive or negative. The surge component can occur at any time in the predicted tidal cycle and have a duration of a few or many hours. The height of the surge component can typically be in the order of 1 m but on occasion can well exceed 2 m (the maximum surge component of the 1953 surge at Southend was nearly 3m). Obviously, if the surge component peaks during the latter part of the ebb tide or at low water there will be little risk of flooding. However, should it peak at or around high water especially on a large spring tide the risk of catastrophic flooding is high unless the flood defence works are adequate and, where necessary, operated. The 1953 the surge component was complex as can be seen from Figure 2.2 below:

6

5

4

3

2

1 Elevation (m ODN) 0

-1

-2

-3 024681012 Hours

Surge Recorded water level Predicted water level

Figure 2.2 The 1953 surge

The peak of the surge occurred towards the end of the flood tide and had a magnitude of 2.88 m. One of the effects of the surge was to advance the timing of high water by more than almost an hour. At the time of the predicted high water the surge component had fortuitously fallen to 2.0 m. Unusually a second surge component occurred early in the ebb tide which had a magnitude of about 2.5 m and lasted for more than 2 hours. Quite clearly a simplistic statement that “high water was raised by 2.0 m” is not

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 12 adequate to describe how close the disaster of 1953 was to a catastrophe. Had the first surge occurred even a few minutes later or worse still at the time of predicted high water or the second surge occurred earlier the water level at Southend would have been up to 0.88 m higher, a level far higher than was attained which in itself remains the highest ever recorded. It should also be remembered that the predicted tide was only 2.57m OD, which is more that 0.3m below a mean spring tide.

6

5

4

3

Elevation (m ODN) 2

1

0 0 102030405060708090100 Distance from Southend (km)

Highest recorded Mean high water spring

Figure 2.3 The 1953 and mean spring high water levels

Gilbert and Horner provide a good description of surge tides that fall into the same category as the 1953 event.

Surge tides in the North Sea have their genesis off the coast of Canada in the region of the Newfoundland Banks. Areas of low atmospheric pressure, or depressions, arise as a result of the meeting of the warm Gulf Stream and the cold Labrador Current off the Labrador coast. Cyclonic winds are generated around the centres of these depressions and, as a result of the wind patterns in the Northern Hemisphere, these depressions move eastward across the Atlantic towards Europe. Atmospheric pressure affects the level of the sea: high pressure depresses the surface and low pressure raises it. Beneath the depression a hump of water forms, only about a foot high but a thousand miles in diameter and moving at perhaps 40 or 50 miles an hour. Many million tons of water moving at this speed represent an enormous amount of energy and the dynamic effect of the eastward movement magnifies the height of the hump, which is further increased as it moves from the deep waters of the Atlantic into the shallower waters of the continental shelf.

Usually these depressions move north-east between Iceland and Scandinavia and do little harm. Occasionally, and unpredictably, they turn east and pass across northern Germany. This brings the hump of water into the northern North Sea. If the depression is a deep one with high pressure to the west, then very strong

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 13 northerly gales will blow on the flank of the depression, and the hump of water is driven south into the funnel formed by the converging coastlines of England and the Continent. This amplifies the hump, which is further increase by the drag of the wind on the surface of the sea. As the water moves south the rotation of the earth throws the water against the east coast of England, following the pattern of movement of the astronomical tide. The Straits of Dover are too narrow and shallow to allow the large volume of water to pass through. The speed of movement of the depression and the period of time over which the strong northerly gales continue to blow now become important factors. If the high wind strength continues in the same area as high water of the normal predicted tide, then the level of high water will be much increase………….

So far we have only been concerned with the surge tides in the open sea, the problem as it is outside the Thames Estuary, and as recorded on the tide gauge at Southern. Surge tides, however become more serious at points higher up the estuary. When a wave enters a V-shaped or trumpet-shaped estuary will build up as it reaches the narrower part……….

As a result of the shape of the Thames Estuary a spring tide, which occurs every fortnight, when the gravitational forces of the sun and moon work together, will normally reach a level at London Bridge which is a metre higher than the level reached at Southend on the same tide.

A surge tide component can also be generated in the Thames Estuary by the movement of a depression moving in an easterly direction on a different course to the 1953 surge in the vicinity of the British Isles. Whilst the process maybe slightly different to that of the surge described the result is similar.

The duration of an individual surge or group of surges can vary between a few hours and, if a number of weather systems combine, a few days. Correlation of the shape of surge, its height and duration require investigation. Initially this work can be confined to the water levels recorded at Southend and Sheerness immediately preceding, during and following a surge event. These data sets will identify the true surge as at these sites the influence of fluvial flow can all but be ignored – an element that has not always been acknowledged as an influential component when assessing up-estuary “tidal” water levels. The weather systems driving the surge should also be included in the assessment.

In addition to the risk of surge tide inundation there is a combination of events that could create a significant flood risk especially in the upper reaches of the tidal Thames and some of its tributaries. These up estuary in-combination events occur on the tidal Thames when fluvial river flow is high during periods of large non-surge spring tides, which would otherwise not necessitate closure of the Barrier. If a large predicted tide has a high or near high water surge component the flood risk will be greater for a given fluvial discharge. The impact of surge tides and / or in-combination events in each tributary and tidal creek requires individual assessment and a flood risk management strategy developed.

It has been noted that there could be pattern where just after low water on rising spring tides when there appears to be a positive surge with no apparent driving mechanism.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 14 The difference between actual and recorded levels, which can be in excess of 1 m, follows a pattern that suggests the predicted tide could be in error. Examination of this ‘phantom surge’ is necessary to reduce the unnecessary activation of flood defence measures being activated. This work should be undertaken in association with the present flood warning arrangements that are managed by POL and UKMO.

2.2.4 Rainfall and catchment run-off Whilst it will not practical to include the whole of the Thames River Basin (shown in Drawing 02) within a single Flood Management study, it is important to recognise the influence that the wider catchment has on flood management within the estuary.

Any change to the rainfall pattern or intensity or the catchment run-off characteristics will have an impact on flood levels at and in the vicinity of the zone where fluvial and tidal flows interact. Storage volumes in areas used to store catchment or fluvial flood waters will similarly be affected, when the area is tide locked by barrier/sluice operation.

With regard to tide locking of tributaries on the tidal Thames, the extent of the existing problem needs to be understood. A strategy is also needed for development planning in the lower reaches of these rivers. At present the flood defence standard for tidal inundation from the tidal Thames is nominally 1 in 1000 years, but the standard of defence for fluvial flooding caused by tide locking is lower than this and the risk of flooding by other means (e.g. pluvial or sewerage) may different again. The merits of a consistent policy and standard of service against flooding deserves further consideration for the tributaries and the tidal Thames Estuary.

Future flood risk caused by tide locking will depend on changes in fluvial inflows, changes in tidal water levels, and changes in land use in the flood risk areas. The impacts for each tributary will require investigation. It is likely that this work would form part of Flood Risk Management in the Thames Estuary project as tidal water levels are a contributory factor to the flooding. However any measures are recommended, these must be reviewed in the relevant CFMP as part of the integration process between Flood Risk Management in the Thames Estuary and the CFMPs.

A full description of catchment issues is provided in Appendix A.

2.2.5 Morphology Riverbed levels in the tidal Thames have been very well documented since the beginning of the last century by the Port of London Authority and before that (post at least 1830) the Admiralty. Regular bathymetric surveys of the whole of the river from Teddington to seaward of Southend enables a clear understanding of the morphological evolution of the estuary whether as a result of natural or anthropogenic activity. The morphology of the river has an impact on tidal water levels. It is reported (Muir Wood 1990 as an example) that extensive dredging of the River Thames led to a significant increase in tidal range at London Bridge in the nineteenth century. The impact of other extensive dredging in the twentieth century should be examined. It is important to assess the impact of dredging and the possibility of other activities, for example the potential impact of more frequent Barrier closures, on river morphology, as morphological change will impact upon the ecology of the estuary.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 15 The Thames Estuary occupies part of the London tectonic basin, which has an underlying Palaeozoic structure overlain by a relatively thick layer of Cretaceous and Tertiary sediments. As shown in Drawing 03, the rims of the basin are formed of chalk and underlying the main part of the basin is a thick series of Palaeocene and Eocene sands and clays of fluvial, estuarine and marine origin. At the base are Thanet Sands and Arenaceous Reading, Woolwich and Oldhaven Beds, extending to the Medway and Swale estuaries. Covering these beds over most of the basin is London Clay, which outcrops extensively along the shore in the region of Southend-on-Sea and the Isle of Sheppey. Finally, there is a covering of fluvial flood plain deposits over much of the area, outcropping along the Estuary at Foulness, Canvey Island, Cliffe, Isle of Grain and the Isle of Sheppey.

The bed material of the Thames Estuary consists of a complete mixture of sediments ranging from coarse non-cohesive gravels, through sands, to fine cohesive muds. In general, the upper reaches are characterised by muddy deposits on the intertidal areas, with more mixed sediments in the sub-tidal zone, whereas in the outer parts of the Estuary, the intertidal areas are more sandy as a consequence of the more exposed environment.

Since 1957, when Inglis and Allen presented their paper “The regimen of the River Thames Estuary as affected by currents, salinities and River flow” (Inglis and Allen 1957), knowledge of the sediment movement in the Estuary has improved. This is primarily a result of the long term monitoring of suspended solids as part of the Thames Barrier project and more generic research studies which have enhanced overall understanding, especially concerning the transport of cohesive sediments.

For the last few centuries the morphological regime of the Thames Estuary has been subject to much change because of the considerable and varied demands put upon it by riparian activity. Little overall strategic management of the activities was exercised until comparatively recently, which makes it extremely difficult to determine what impact had what effect. Since the late 1960s / early 1970s large capital or maintenance dredging programmes, the discharge of polluted effluents, the construction of riverside developments all of which could have had a significant influence on the flow regime of the estuary have been subject to restrictions and increasing investigation to ensure that their impact is acceptable to the river regime. Since 1970 changes in the riparian activities and the implications of legislation has enabled the estuary overall to establish a regime that has substantially been allowed to develop more naturally than for many previous decades, perhaps centuries.

Morphological change primarily since 1970, but with reference to the nineteenth century, has recently been examined for limited stretches of the tidal Thames as part of investigative studies. The extent of change identified in the areas examined shows how the estuary has been developing. This work should be extended to the whole of the tidal Thames between Teddington to a point seaward of Southend to establish the changes that are taking place, how they interact with changes to tidal water levels and to provide background and base data for the Thames Flood Risk Management studies.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 16 2.2.6 Waves The extensive offshore bank and channel system located to the east of Southend protects much of the estuary from the long period southern North Sea storm waves. Wave activity in the tidal Thames west of these banks is generated by two sources.

The first type of wave to be considered is related to wind speed and direction and the available fetch over which waves can be generated. Generally downstream locations are more exposed to the wind driven wave activity than upstream locations.

Throughout the tidal Thames the passage of vessels using the river also creates waves. These waves although individually of much less energy than the wind driven waves found in the seaward parts of the tidal Thames Estuary are of significance, especially in areas which are more protected from the wind.

2.2.7 Winds It has been established that there is a significant difference in the mean trends of water level set-up values associated with the east and west winds. In general, east and west winds of up to 40 knots can be expected to cause respectively an increase or decrease of water level at London bridge relative to Southend, of up to 0.3m (HR Wallingford 1971). Wind will also impact on wave activity especially in the Lower and Outer Estuary (HR Wallingford 2001a).

2.2.8 Climate change Projected sea level rise, increased fluvial flows, increased storminess, greater wind speed are all issues that will impact on many of the drivers of flood risk in the Thames Estuary. UKCIP 2002 suggest that an appropriate precautionary allowance of 800mm rise to high water levels in Central London whether from the tidal surges or increased fluvial flow should be considered for 2080. However, it is acknowledged that this prediction requires review as the modelling used may not have been adequately robust for this prediction to be applied with a high degree of confidence. A range of scenarios will have to be examined and updated to accommodate any modification to the predicted climate changes.

The importance of having a good and robust understanding of the potential impact of climate change on tidal water levels is essential, as tidal water level and increased tidal energy are the principle drivers of not only flood risk but the future well-being and ecological function of the estuary.

2.3 Hydraulic drivers and ecology

The hydraulic drivers affecting flood risk also determine the ecological conditions within the estuary and its associated tidal tributaries. In this respect, engineering interventions and management options designed to reduce flood risk impinge upon the ecological structure of the estuary and the environmental services provided by unimpaired ecological function.

The main drivers for the ecological component of the estuary are:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 17 S The dynamic interaction between morphology and hydrology of the system. This directly determines the quantity of habitat available for the dependent species of fauna and flora and indirectly, influences the quality of these habitats. S Water quality and pollution. Pollution and oxygen depletion continues to affect the biological integrity of the estuary on an episodic and chronic basis, at least locally. S Productivity as determined by the food-web characteristics of estuarine systems. This is influenced by the magnitude of both fluvial (including sewage works and other anthropogenic discharges) and marine inputs as well as the extent of ecological habitat elements within the system. S Disturbance regimes. This includes the impacts of dredging, commercial fishing methods and some human recreation activities, which affect habitat quality and integrity.

The presence of structures within the tideway has significant effects upon the ecological dynamics of the estuary. The morphology of the estuary and the habitats associated with particular morphological features is still thought to be in the process of responding to the effects of the tidal defence works implemented in the latter half of the 20th century. These works, combined with relative sea level rise, are thought, at least locally, to be responsible for a significant loss of upper intertidal, saltmarsh and brackish marsh habitats in the Thames. In some instances these features may have comprised an integral part of the tidal defences.

2.4 Overview of the defence system

Tidal defences in the Thames Estuary were significantly improved during the late 1970’s and early 1980’s through the construction of a moveable barrier at Woolwich and extensive raising of the tidal embankments and walls as far as Southend-on-Sea and the Isle of Grain. Nearly all of the defences were designed to provide protection against a 1:1000 year event as predicted the time of design for the end of the design life (2030). The only exception was Cliffe marshes in Kent, where such a high level of defence could not be economically justified. The design level, known as the ‘Dartford envelope’, included an allowance for a reflected wave (caused by barrier closure) and varied between approximately 7m (ODN) at the Woolwich barrier and approximately 5.7m(ODN) at the outer part of the estuary (Trafford 1981).

The actual level to which the defences were constructed varied as an allowance was also included for settlement of the earth embankments. Upriver of Woolwich some of the interim defences, which had provided protection during the construction of the barrier and associated works, were removed. The location of the main elements of defences is shown in Drawing 04 and summary descriptions are provided below. The defence system is more fully described in Section 3.3.

2.4.1 Responsibilities and legislation There were four client organisations for the tidal defences constructed in the late 1970s and early 1980s:

i. The , responsible for the defences from the Woolwich barrier to Barking Creek / Dartford Creek

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 18 ii. The Thames Water Authority responsible for defences on the north bank between Barking Creek and Purfleet (including the Barking Creek Barrier)

iii. The Anglian Water Authority responsible for defences on the north bank between Purfleet and Southend

iv. The Southern Water Authority responsible for defences on the south bank between Dartford Creek and the Isle of Grain (including the Dartford Creek Barrier)

Responsibility for the tidal defences has now passed to the Environment Agency, with the study area divided between the Thames, Southern and Anglian regions, as shown in Drawing 05. The responsibility for the funding of repairs or enhancements to tidal defences is not always obvious. Although the forerunners to the Environment Agency commissioned the existing defences, which were funded from the public purse, there powers are entirely permissive and thus there is no statutory requirement for the defences to be maintained to a particular standard.

Nationally the provision of land drainage (including protection against flooding) is regulated by the Land Drainage Act 1991 and the Water Resources Act 1991, both of which were amended by the Environment Act 1995. The most recent act gives the Environment Agency general supervision over the flood defence issues and this was further elaborated by the Government in May 1999 (DEFRA 2002a). Local authorities have powers to undertake flood defence works on watercourses which have not been designated as "main" and which are not within internal drainage board areas. Maritime district councils also have powers to protect the land against coastal erosion under the Coast Protection Act 1949. Boundaries for relevant authorities are shown in Drawing 06.

There are, however, several relevant pieces of legislation covering the construction and operation of the tidal defences within London. The Metropolis Management (Thames River Prevention of Floods) Amendment Act 1879 established levels to which Riparian Owners were required to raise flood defences. This was supplemented by additional legislation with the latest amendment in 1962, however it is the levels established in 1930 (5.54m ODN at Hammersmith, 5.28m at London Bridge and 5.18m at Barking Creek) that currently apply. Present defence levels are understood to be significantly in excess of these statutory levels.

The Thames Barrier and Flood Prevention Act 1972 was introduced specifically to facilitate the construction and operation of the Thames Barrier and downstream defences. This included provision for the appropriate authorities in the London and Essex areas to require private frontagers to close flood gates on their land and enable the authorities to close any which remain open. Similar measures are contained in the County of Kent Act (1981) for the defences in that area.

It is understood that historically Thames Region of the Environment Agency has been successful in obtaining contributions of between 10 and 50% from Riparian Owners towards the costs of repairs and remedial works on private frontages.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 19 2.4.2 Tidal Barriers The programme of works in the late 1970s and early 1980s included five subsidiary barriers on tributaries downstream of the principal Thames Barrier at Woolwich. These barriers were constructed at locations where, due to requirements for navigation or other constraints, sluices could not be used:

S Barking S Easthaven S Fobbing S Benfleet S Dartford Creek

Although not on the same scale as the Woolwich Barrier, these structures are nevertheless significant with openings of up to 38m. Substantial floodgates were also provided for the main entrances to the (at the King George V Dock and Gallions Lock) and Tilbury Docks.

2.4.3 Walls, embankments and floodgates In conjunction with the barrier works, downstream defences were raised to provide an increased standard of protection. These defences were the subject of much negotiation and have many different forms since they were largely founded on existing structures and designed with consideration of the needs of the multitude of private frontagers. In urban and industrial areas the defences are typically vertical concrete or steel sheet pile walls, whilst in front of the extensive marshes and agricultural areas they are usually earth embankments, often with a clay core or steel sheet pile cut off.

Frontager floodgates were provided at locations where access was required through the tidal defences for pedestrians or vehicles. Operation of these gates is largely manual and the responsibility of the occupier.

2.4.4 Sluices, tidal flap-gates and pumps Two substantial and sluices were constructed at Mar Dyke and Rainham Creek on the north bank of the river and numerous smaller sluices were constructed at other locations where a controlled discharge in to the Thames was required. These allow tributaries to discharge during normal conditions, whilst still providing a defence against flooding in extreme events. Flap gates and valves in the defences facilitate a large number of smaller discharges into the Thames. Mechanical pumps have also been provided in a number of locations to discharge water that will build up behind the defences in the event that the gravity drainage system becomes tide locked or otherwise ineffective.

2.5 Sediment processes and morphological response

The Thames Estuary Flood Prevention Investigation sediment studies carried out between the late 1960’s and the early 1990’s enabled the effects of a barrier closure on the suspended sediment regime to be examined. As a spin-off from these studies and primarily using spring tide information, as little sediment generally becomes suspended on neap tides, four distinct suspended solids sediment zones can be determined within the tidal estuary.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 20 The first zone extends from the tidal limit at Teddington to approximately Lower Pool. Within this area the suspended solids concentration, due to tidal mobilisation, is low. Between Blackwall Point and Erith (zone two), the stretch of river that includes the mud reaches, the suspended solids concentrations are generally higher than elsewhere in the Estuary and the riverbed and intertidal banks comprise principally fine sediments. Seaward of Erith to Lower Gravesend Reach, zone three, suspended solids concentrations are at moderately high levels with the intertidal foreshore primarily comprising fine muddy sediments. In the fourth zone, Sea Reach and seaward suspended silt concentrations are lower than in zone three and the composition of the bed sediments more variable, London Clay through to gravels and stone being present in this area.

On a large spring tide, starting at low water, a particle of water would move up-Estuary about 12km if it started at Southend, with the equivalent distance at Greenwich being up to 17 km. The particle would pass many potential "sinks" and "sources" especially in areas where there are significant bends in the Estuary. The fine sediments in suspension would only fall to the riverbed when current velocities in the locality are low and would then be eroded when the critical threshold for movement of the bed sediments is next achieved. This critical threshold often occurs when the current velocity is lower than the maximum that would be attained at that point during the next phase of the tidal cycle. Consequently, all of the material suitable for erosion would be carried quickly away from the "source" and the loss of sediment at an individual point would not be a continuous process throughout that part of the tidal cycle.

The vast majority of sediment transported in suspension occurs on spring tides, because the neap tide forces are insufficient to raise more than a minimal quantity of sediment into suspension. Vessel movements also result in local mobilisation of bed sediments but the quantity of sediment transported by this method is small compared with the natural movement of sediment in the Estuary system.

Near bed transport of fine material, which generally involves relatively high concentrations and fluxes, is much less understood. Simplistically, the mobilising force in the Thames appears to be the salt concentration, which, in turn, is a function of freshwater flow. In normal years, freshwater flow is lower in the period April to September than in the winter months (October to March). During periods of low freshwater flow, the average salinity in the area between Blackwall Point and Lower Gravesend Reach slowly increases as it is not diluted or forced seaward by the fluvial flow. This seasonal variation in salinity causes the sediments to migrate up-river to be deposited in areas where the salinity/flow climate is suitable. The change to the salinity regime is slow because the forces are weak and it takes many months for the available sediment to be transported upriver.

In the autumn and early winter, the first freshwater flow of sufficient magnitude to have a significant effect on the Estuary salinity would mobilise these fine cohesive bed sediments. From available documentation it appears that most of this sediment moves as a near bed very high concentration suspension in the deepest parts of the channel, as little evidence of the mass movement of suspended silt sediments was directly detected during the twenty-three years of continuously monitoring suspended silt concentrations carried out as part of the Thames Barrier studies. Whilst a small percentage of the sediment would rise into suspension the mass bed-load sediments would be carried

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 21 many kilometres downriver returning to or near to the position occupied before the ‘summer’ upriver movement of the sediments commenced. The down-Estuary movement of sediments by this method can, within a few days, reverse much of the slow up-Estuary movement that has occurred in the summer.

The coarser sands and gravels that exist in the subtidal areas of the Estuary and in the Outer Thames reaches are transported under the strong tidal currents. In the Outer Estuary, wave effects enhance sediment transport by increasing entrainment from the seabed, and on the exposed coast, wave breaking tends to be the dominant mechanism for littoral drift.

In the Outer Estuary wave action contributes much more significantly to sand transport and the limiting effects of sand supply and muddy sediment are reduced. Sand fluxes tend to be strongest in the deeper channels. Further out to sea the navigation channel passes through a series of sandbanks. These sandbanks can dry at low water and are interspersed by channels with depths below -20mCD. The sandbanks are known to migrate over time but more or less retain constant depths in the channel between them. With distance seaward sand waves become more prominent and can cause some effects on navigation. The outer channel is managed largely through re-buoying when necessary. This policy minimises the requirement for maintenance dredging.

The twice-daily natural tidal distribution of suspended solids or bed-load sediments in the tidal Thames are influenced by many short or long-term factors. Some of these factors can have a very marked and immediate response over large stretches of the tidal Thames whilst the effect of others is more locally confined and more difficult to recognise within the overall structure of the tidal Estuary sediment distribution change.

2.6 Socio – economic constraints and opportunities

2.6.1 Economic and cultural importance London has expanded over approximately 2000 years from a collection of separate villages and settlements to a metropolis that is now the financial centre of Europe and the economic hub of the UK. London has a Gross Domestic Product of approximately £180 billion, greater than all other countries excluding US and Luxembourg (GLA 2002b). Much of London’s early growth was facilitated by the River Thames and the port services the river offers maintains its position as one of the most important commercial ports in Britain. However, financial and other service industries have become increasingly important. The now generates over £30 billion a year for the UK economy with a daily foreign exchange transaction turn-over of US $600 billion - a third of the world total and twice as much as the USA (GLA 2002b). London is also home to the Government and much of the political activity in the UK, it is a key tourist destination and a centre of educational, cultural and artistic activity.

2.6.2 Existing infrastructure and constraints More than 75% of the tidal flood defences within Thames Region of the environment Agency are located in urban areas. The River Thames, as is now stands, is largely artificial, hemmed in by embankments and developments on the natural floodplain. However, further down river the constrictions are less intense and although the river is effectively constrained by the existing flood defences the landscape is much more dominated by open natural and industrial areas with limited urban frontages adjacent to

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 22 the river. The length of defences classified by the immediate hinterland is shown in Table 2.2 below:

Table 2.2 Classification of flood defences by immediate hinterland

Approximate length of flood defences (km) Thames Region Anglian Region Southern Region Total Urban areas 173 22 12 207 Other areas 47 52 30 130

Within urban areas the existing defences are predominantly hard, comprising vertical or steeply sloping steel, concrete or masonry walls, many of which provide limited habitat or public amenity. Many of the defences were developed in a piecemeal fashion and even where they were raised to a uniform level the underlying defences are often only consistent over very short lengths. Ownership and maintenance responsibilities for the defences are frequently not well defined (particularly where the hinterland has been redeveloped) and access to the defences is often difficult. Working methods for inspection, maintenance and repair will often be constrained by access limitations and the proximity of residential properties. The infrastructure within the city is under heavy pressure and whilst it is an increasingly expensive place in which to live and work, there are also areas of severe social and economic deprivation in which frontager contributions for maintenance and repairs may be difficult to obtain.

2.6.3 Development opportunities, population and housing With much of the recent expansion of London taking place in the west, the more industrial and largely deprived eastern part of the city now provides many of the opportunities for (re)development of commercial and residential property. This started with the redevelopment of the Docklands from a predominantly industrial to commercial and residential uses in the 1980s, and opportunities are now being explored in the corridor further to the east alongside the Thames.

This potential has been recognised by both the Government and local organisations that have formed a series of partnerships to plan the development of the Thames Gateway area. The Greater London Authority is also active in planning for future growth to the east of London. Plans for development are subject to a process of constant change and refinement, but useful information is provided within ‘Going East: The Economic Strategy of the Thames Gateway London Partnership’ (TGLP 2001) and ‘The draft London Plan’ (GLA 2002a).

The population within the indicative tidal flood risk area is just over 900,000 people with, as can be seen from Drawing 07, the majority concentrated within Greater London and other urban areas. The population within the estuary as a whole is expected to increase dramatically in the coming years, in the same way that the population of London, which grew from 6.8 million to 7.4 million in the last 15 years, is predicted to exceed 8 million in the next 15 years (GLA 2002a). In addition to the people living within the flood risk area, those working or visiting shops or amenities in the floodplain would also be affected by any significant flooding. This number is also expected to continue increasing at a dramatic rate with 5.1 million new jobs in London expected by 2016 (GLA 2002a) and significant demand for new housing and commercial property.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 23 Much of the Thames Gateway area, which has been identified as a national priority area for regeneration, will benefit from significant improvements in infrastructure links including the Channel Tunnel Rail Link. Latest estimates (GLA 2002a) are that there will be 23,000 new dwellings in London every year up to 2006 and 7.4 to 8.6 million square metres of new office space. Many of the areas identified for development are located within the floodplain. These areas are presently protected by the defences constructed in the late 1970s and early 1980s, but with the changing land use comes a significant opportunity to modify the defences to a more appropriate form (and possibly alignment). There may also be opportunities for environmental benefits, increased access to the river (possibly including the cycle network proposed by SUSTRANS) and safeguarding of land for the continued maintenance and development of the defences.

There may also be opportunity for joint funding of works where private developers are undertaking works which are dependent on the continued integrity on the tidal defences and there will be opportunities to ensure that any maintenance, repair or enhancement of existing defences incorporates best practice with regard to sustainability and the environment.

2.7 Recommendations

1. The advice of the Port of London Authority and operators will be of paramount importance to assess the potential future navigation needs, as for example, the present navigation requirements may change in the coming years.

2. For the purpose of the Thames Flood Risk Management studies it will also be of considerable importance to understand the potential total discharge into the different parts of the estuary from the various sources (particularly CSOs) and the impact this will have on upriver storage capacity when barriers are closed.

3. At present the flood defence system in some of the creeks and tributaries is based on a combination of flood defence wall and a barrier or control structure. The closure of the barrier or control structure is often directly linked to the closure of the Thames Barrier. This policy was determined using the catchment criteria available at the time of the Thames Barrier study. The catchment criteria used at that time should be reviewed to determine their relevance for present and future Flood Risk management.

4. Advantage should be taken of any opportunity to clarify the level of each tide recording location. This should be carried out as soon as possible and additional tide recording locations established within the tidal estuary. An assessment of the potential impact of Ocean and Earth Tides on tidal water levels should also be undertaken to determine the through-tide variation at individual locations and from location to location at a given time.

5. Correlation of the shape of a surge, its height and duration require investigation. Initially this work can be confined to the water levels recorded at Southend and Sheerness immediately preceding, during and following a surge event. These data sets will identify the true surge as at these sites the influence of fluvial flow can all but be ignored. – an element that has not always been acknowledged as an

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 24 influential component when assessing upestuary “tidal” water levels. The weather systems driving the surge should also be included in the assessment.

6. A pattern has been suggested where, just after low water on rising spring tides, there appears to be a positive surge with no apparent driving mechanism. The difference between actual and recorded levels, which can be in excess of 1 m, follows a pattern that suggests the predicted tide could be in error. Examination of this “phantom surge” is necessary to eliminate flood risk measures being unnecessarily activated.

7. It is reported that extensive dredging of the River Thames led to a significant increase in tidal range at London Bridge in the nineteenth century. The impact of other extensive dredging in the twentieth century should be examined.

8. The potential impact of more frequent Barrier closures, on river morphology, as morphological change will impact upon the ecology of the estuary and should be investigated.

9. Detailed assessment of the morphological change for the whole of the tidal Thames between Teddington to a point seaward of Southend since 1970 should be carried out to establish the changes that are taking place, how they interact with changes to tidal water levels and to provide background and base data for the Thames Flood Risk Management studies. Older historical data (including 19th century data) should be included but not in such detail.

10. The importance of having a good and robust understanding of the potential impact of climate change on tidal water levels is essential, as tidal water level is the principle driver of not only flood risk but the future well being ecological function of the estuary. UKCIP 2002 provides appropriate precautionary advice, but this is not likely to be adequate for the complete range of tasks that will require examination as part of the Thames Flood Risk Management studies.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 25 3. THE PHYSICAL ENVIRONMENT

The following issues must be examined and assessed both individually and collectively to determine their impact(s) on tidal water levels and flooding.

3.1 Hydraulic drivers

The hydraulic drivers of flood risk were introduced in Section 2.3. This Section details the data that is available for the studies that will form the next stage of the Thames Flood Risk Management programme. The outline of an assessment programme is given to inform the required studies. Available data is described and summarised within Drawing 08, gaps in the data and, where necessary, the requirement for better quality data than presently available are also provided. Measurement programmes (specification and time-frame) for the collection of the required data are described with cost indications.

Some of the issues listed under an individual heading have previously been assessed individually. These studies will be integrated into the overall examination of tidal water levels.

3.1.1 Water level including surge component The height to which water levels can rise as a consequence of a surge tide or an in- combination event where tide and fluvial flows combine are the primary drivers of flood risk along much of the estuary. In the Lower Estuary and beyond fluvial flow becomes of less significance but this is offset by wave activity, which becomes greater the further seaward the location. Tidal water level is the common factor and therefore the availability and accuracy of the data is of considerable importance.

The Environment Agency and the Port of London Authority at a limited number of positions presently carry out Continuous monitoring of tidal levels in the Thames Estuary. Historically the Port of London Authority and the predecessors of the Environment Agency have recorded tidal water levels at various points along the estuary with the data generally being of good quality. At all locations the gauges have been and are referenced to Ordnance Datum bench marks, which in most instances have not been accurately calibrated for more than forty years.

Available data and quality A number of these historical tidal records, from the Environment Agency and Port of London Authority, have been used in previous studies at HR Wallingford. HR Wallingford holds the data summarised in Tables 3.1 and 3.2.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 26 Table 3.1 Environment Agency water level data

Location Richmond Chelsea W’minster Tower Erith Tilbury Sh’ness Southend Pier Year 1988 * * 1989 * * * * * * * * 1990 * * * * * * * * 1991 * * * * * * * * 1992 * * * * * * * * * 1993 * * * * * * * * * 1994 * * * * * * * * * 1995 * * * * * * * * * 1996 * * * * * * * * * 1997 * * * * * * * * * 1998 * * * * * * * * * 1999 * * * * * * * *

All of the above are recorded tidal levels relative to Ordnance Datum. The data are at half-hourly intervals with times to Greenwich Mean Time. It is assumed that additional years of tidal data can be supplied if required.

Table 3.2 Port of London Authority water level data

Location Coryton Tilbury Southend Margate Year 1994 * * * * 1995 * * * * 1996 * * * * 1997 * * * * 1998 * * * * 1999 * * * * 2000 * * * *

All the data from the Port of London Authority is supplied in the form of the predicted tidal level and actual recorded level at half-hourly intervals. Water levels are referenced to local PLA datum and times to GMT. It is understood that additional data can be obtained from these locations for other years if required.

In addition to the tidal data recorded along the estuary, historical tidal data would be required from the tributaries to the Thames Estuary. At the very least all tide gauges, past and present, in the whole Estuary system should be identified and all archived tidal data should be made available from these gauges.

The Environment Agency and Port of London Authority data are generally of a good standard. There is a need to establish that the datum to which they refer is sufficiently accurate for the Thames Flood Risk Management studies.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 27 Possible providers of additional tidal data S Port of London Authority S Environment Agency S Medway Ports Authority S S Admiralty S HR Wallingford archives

Assessment programme The following tidal water level issues will require examination: S Longitudinal profile(s) S Typical tides and tidal cycle S Extreme tides S Surge components S Range of surge component heights and durations S The variability of tidal levels in the tributaries S The interaction of Thames tides and those in the tributaries S Fluvial discharges (Thames, tributaries, storm water and other outfalls) S Clarification of accuracy of measuring location height S Clarification of the impact of changes to the tidal range as a consequence of large scale dredging campaigns or bridge structures.

Data requirements It is strongly recommended that clarification / confirmation of the accuracy of the Ordnance Datum for each of the tidal water levelling locations is addressed as soon as possible. This recommendation is made because the uncertainty relating tidal water levels could lead to inaccurate or misinterpreted analysis of past and present tidal information. This could potentially seriously impact upon projected tidal propagation, which in turn is fundamental for the examination of how the hydrodynamics, morphology and environmental function of the estuary will be influenced in the future by the Thames Flood Risk Management Strategy adopted.

Recent studies indicate that there is differential ground movement in the tidal Thames basin and that generally ground levels are rising (IESSG and BGS 1999). This complicates the understanding of tidal propagation in the estuary to a point where accurate analysis of the impact of sea level rise relative to the land, the confidence level that can be given to the effect of fluvial flow on tidal levels or modelling studies may therefore be inadequate than ideally required for the Thames Flood Risk Management Studies.

There is a need to establish additional water level measurement points, especially upriver of the Barrier, to provide a more robust understanding of the interaction of fluvial and tidal levels in this very sensitive stretch of the river. This also applies to the system of tributaries flowing in to the estuary.

A common archiving system for all existing and future Thames tidal data should be established as soon as possible. It is recommended that data archived is stored at no greater than ten minute intervals and that predicted tide and surge component is included. The Port of London already uses a similar procedure.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 28 3.1.2 Fluvial flows Knowledge of the long-term fluvial flow discharge characteristics from the non-tidal Thames, its tributaries or from industrial or Combined Sewer Outfalls into the tidal Thames is essential if the impact of these flows is to be adequately modelled. High fluvial flows can have a serious flood implication. Low flows or management of the flows which in the long–term will change the flow distribution characteristics can have an impact on the distribution of bed sediments and the salinity concentrations within the tidal river.

Available data and quality In addition to the fluvial inflow from the Thames at the tidal limit, tributaries and creeks also discharge into the Thames Estuary, as summarised in Table 3.3

Table 3.3 Tributaries and creeks discharging into the Thames Estuary

South Bank North Bank Beverly Brook Bow Creek (River Lee) River Wandle Barking Creek (River Roding)* Deptford Creek (River Ravensbourne and Rainham Creek River Quaggy) Dartford Creek (River Darent) Mar Dyke Cliffe and Highham Creeks Mucking Creek Pitsea Creek River Cray River Beam River Crane River Ingrebourne River Brent *See note below Table 3.5

In addition to the water courses identified above there are a number of significant consented discharges into the Estuary. Dry weather STW flows from 1995 are shown in Drawing 09 and summarised in Table 3.4 below:

Table 3.4 Consented discharges into the Thames Estuary in 1995

Location Effluent type M3/day Mogden STW Sewage effluent 420,000 Kew STW Sewage effluent 6,000 Tate and Lyle Trade 41,000 STW Sewage effluent 1,000,000 Crossness STW Sewage effluent 550,000 Purfleet Board Mills Trade 6,000 Long Reach STW Sewage effluent 190,000 Cory Aggregates Trade 7,200 Scott Ltd Trade 12,600 Tilbury STW Sewage effluent 10,700 Gravesend STW Sewage effluent 4,200 Canvey Island STW Sewage effluent 5,300 Southend STW Sewage effluent 36,500

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 29 In addition to the above list are cooling water systems, of which there are a number along the Estuary, for which discharge consent has been granted. It is assumed that extraction from and the discharge to the river and as such will not directly influence the total volume of water within the estuary.

Consented discharges into the tributary system must also be considered and are shown in Table 3.5.

Table 3.5 Consented discharges into tributaries in 1995

Location Effluent type M3/day River Roding, Beckton STW* Sewage effluent 16m3/s . This emergency discharge only operates when normal Thames riverside outfall is tide locked. River Ingrebourne, Riverside STW Sewage effluent 110,000 Dartford Creek, Wiggins Carbonless Papers Trade 10,000 Mucking Creek, Standford-le-Hope STW Sewage effluent 4,400 Pitsea Creek, Basildon STW Sewage effluent 9,500 Benfleet Creek, Benfleet STW Sewage effluent 6,100 * A study by Halcrow investigated the significance of this discharge in respect of its influence on water levels within the River Roding in the event of Roding Barrier closure. They concluded that when considering the 75m3/s Roding fluvial flow event in October 2000 in comparison to the same fluvial event with zero STW discharge that:

" the addition of the Beckton STW discharge is not significant, however, at a lower Roding fluvial flow the addition of the Beckton STW discharge could become the primary cause of flooding'.

It should be noted that the Halcrow study was confined to the maximum water level and hence the risk of flooding. No consideration was given to the duration of the flooding, which it is reasonable to assume would probably have been of greater duration with the STW 16m3/s than if there had been zero flow.

Further to these there are a further ten discharge consents At Shellhaven / Thameshaven for up to approximately 500,000 m3/day of a mixture of trade effluent, cooling and surface water. Some of these discharges may have now ceased due to changed use of the riverside facilities (NRA 1995).

It is known that the Environment Agency record volume flow rates on a number of the tributaries and it is assumed that the water companies keep records of the flows that they discharge. Historical data would be required from all of the above sources in order to assess any change to the discharge patterns and hence the potential impact on the Estuary and flood levels.

3.1.3 Combined Sewage Overflows There are many Combined Sewage Overflows (CSOs) discharging into the tidal Thames or its tidal tributaries. A list of the discharges upriver of Charlton appears in Appendix C. The total discharge from the individual CSOs listed is understood to be between 1 Mm3/day and a maximum of about 5 Mm3/day. Information of the CSOs down-estuary of Charlton has not been obtained.

These data are generally considered to be of at least a good standard. Some of the information refers to licensed discharge other data is actual discharge.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 30 Providers of fluvial flow data S Environment Agency S Local Authorities S Water companies S Commercial organisations with discharge consents

Assessment programme S Identify data gaps and obtain data or establish flow measurement systems where necessary. S The range of flows and their impact S The discharges from all fluvial sources (Thames, tributaries, storm water and other outfalls) S Time-series flows and rolling volume (any 12.5 hour period – a tidal cycle) S Impact of fluvial flows on tidal levels S Impact of high fluvial flows on extreme tidal levels. S The changing distribution of fluvial flow event. S The impact of water abstraction on the distribution of fluvial flows

Data requirements It is anticipated that sufficient data will be available for the initial stages of the above assessments. If data gaps are identified there may be a need to establish flow measurement systems. This could even apply to the small creeks if there are environmental issues or riparian activities that could be impacted upon by a changed pattern of discharge.

3.1.4 Tidal currents As part of the Thames Barrier and associated flood defence studies a major simultaneous measurement programme was carried out at twelve locations in the Thames Estuary for four different flow conditions, namely spring and neap tides with low and high fluvial flows at Teddington. The measurements were taken in September 1968 (high fluvial flow) and September 1969 (low fluvial flow). No other estuary wide contemporary simultaneous information is available.

The need to understand the tidal current regime within the estuary is essential for both local and estuary-wide reasons and to provide the information to support the investigation of other issues, which would include but not be limited to: - S Navigation of the tideway, especially commercial, is often dependent on working with the tidal strength. S Accretion, erosion and hence river morphology is strongly influenced by the distribution of current velocities. S The stability of intertidal areas and riverside structures S The integrity of the river ecology S Dispersion of effluents.

Available data As part of this survey programme through-depth current velocities were taken at each of the following locations. Other data recorded at the same time as the current velocities is included and all are documented in HR Wallingford Reports (EX 543 to EX554) as shown in Table 3.6.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 31 Table 3.6 Tidal current data

Report Spring tide Spring tide Neap tide Neap tide Location No High FF Low FF High FF Low FF EX543 Syon Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX544 Corney Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX545 Chelsea Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX546 Upper Pool CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX547 Limehouse Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX548 Woolwich Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX549 Barking Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX550 Halfway Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX551 Long Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX552 Gravesend Reach CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX553 Coryton CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC EX554 Southend CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC CS, Sal, SSC Note: FF= Fluvial flow CS = Current speed Sal = Salinity SSC = Suspended Solids Concentration

While it is appreciated that these data are over 30 years old they are still used when suitable up to date data is not available. However, there have been significant changes to the margins of the Estuary, including construction of the Barrier and the removal of disused jetties, construction of new riverside facilities, the removal of the old London Bridge – on-going at the time of the surveys - and the construction of the Queen Elizabeth II and Millennium Bridges.

These data enable the following to be determined at the point of measurement:

S the range of flows within the estuary S the flow variability through tide and depth S the spring /neap tide variability S the influence of fluvial flow.

This information provided much of the current velocity data for the whole of the Thames Barrier studies and although dated is still of considerable importance as it is the only estuary-wide current velocity data set.

Since the 1968 / 1969 measurement programme many individual current velocity surveys have been carried out. Whilst these data sets are individually important they do not provide an even or reasonable coverage of the river current velocity regime even in a short stretch of the river. At an estuary wide scale these data should only be used as support information and not used for general assessment of the river regime. In recent years current velocity measurement programmes have used vessel mounted Acoustic Doppler Profiling (ADP), which enable a good understanding of the full river-width current velocity distribution to be obtained at intervals through the tidal cycle.

These ADP data sets extend from Canvey Island in the east to in the west. Table 3.7 which lists the locations from the seaward end working upriver, summarises the data obtained all of which unless otherwise marked were on spring tides only.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 32 Table 3.7 ADP data sets

Location Client Date Lower Hope Reach to Canvey Island P & O and PLA 2001 ** Tilbury Power Station Innogy 2002 Northfleet Hope Tilbury Container Services 1999 Erith Rands Port of London Authority 2002 Erith Reach Port of London Authority 2002 Lower Woolwich to Halfway Thames Water 2002 Reaches Blackfriars to Southwark Bridges Marchioness Inquiry and 1999 Millennium Bridge Hungerford Bridge London Underground Limited 1998 Consultant 2002 Vauxhall Bridge St George’s 2000 **Spring, part Mean and Neap tide

Data requirements and assessment programme Changes to the river regime since the 1968 and 1969 surveys, whether perceived or actual need to be examined and to do this contemporary data is required. Today measuring techniques enable full river-width measurements to be taken through-tide. It is recommended that a programme not dissimilar to that carried out for the Thames Barrier study be undertaken to provide the new round of studies with data appropriate to the task. The programme should include current velocity measurements in the Outer Estuary and tidal water levels throughout the estuary. These data, to be collected to a programme that will be based on spring and neap tide data for both high and average/low fluvial flows, will enable contemporary examination of the following: -

S The range of flows and their impact on a river cross section S Variability through tide, depth and position on the cross section S Spring /neap tide variability S The influence of fluvial flow S The influence of salinity on gravitational flow

3.1.5 Waves At the upper end of the estuary wave action is probably insignificant due to the shielding of short fetches afforded by building near to the river banks, further down the river (below the Woolwich Barrier) there is more opportunity for local wave generation which may have a significant effect on water levels. In the Lower Estuary the wave climate is more dynamic and is primarily locally generated. Long period swells originating in the North Sea are not thought to penetrate into the Lower Estuary.

Available data Existing wave prediction and measurement locations within the estuary are summarised in Drawing 10.

Possible providers of wave data S HR Wallingford S British Oceanographic Data Centre

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 33 Assessment programme S The varying wave climate through the Thames Estuary S The meteorological influence S Shipwash

Recommended programme of site studies While it is possible to predict local wave climates, it is recommended that a suitable series of wave measurements be undertaken to directly measure the variation in wave climate along the Estuary. This programme of work should include the measurement of the offshore directional wave climate and, simultaneously, the directional wave climates at a number of locations in the lower and middle Estuary. Records of meteorological conditions should also be made at each of the sites.

3.1.6 Wind As well as generating short period waves wind can influence the tidal height resulting in set-up or set-down.

Available data The United Kingdom Meteorological Office is the prime recorder and archivist of data in the country. Additionally, it is known that some wind records are available for Dartford Crossing, Dartford Creek Barrier and from the Port of London Authority.

Possible sources of meteorological data S HR Wallingford S UK Meteorological Office S Port of London Authority S Operators of the Dartford Bridge S The Environment Agency S Southend or Manston Airports

Assessment programme The impact of wind strength and direction on tidal range and shape locally and throughout the tidal estuary

Recommended programme of studies Historical records of atmospheric pressure, wind speed and direction should be obtained for locations along the estuary. These records ideally should have be made at the same time as the tidal records and included in the recommended tidal level archive.

3.1.7 Joint probability Individually each driver of flood risk is very important. Some of the drivers can cause flooding with little help from of any of the others. Obviously if more than one driver combine the flood risk can be greater. If all act together, the joint probability, a surge event greater than 1953 could occur.

Assessment programme Using the data from all of the individual assessments a range of joint probabilities should be examined. This will provide appropriate guidance to the Thames Flood Risk Management of the importance and relevance of the individual components

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 34 3.1.8 Structures Some of the historical data that will probably be used in the Thames Flood Risk management studies will have been subject to the influence of structures, for example the afflux at multi-small arched bridges would have been much greater than that of the new bridges that replaced them.

Available data and potential data sources

A wide range of data (ranging from drawings and paintings through to detailed design drawings) is understood to be available from the following organisations

S British Museum S City of London S Greater London Authority S Institution of Civil Engineers S S Port of London Authority

Assessment These data need to be reviewed to enable historical water level data to be put into context.

3.1.9 Managed setbacks and reclamations There are no instances of managed setbacks, that is the deliberate flooding of rural areas by realignment of the flood defence line, within the tidal Thames Estuary. At the London Dome site the hard flood defence line was withdrawn and the bank and intertidal foreshore fronting the defence line terraced to offer a softer defence to the river. The findings of this work requires documentation.

Over the last decade or so there have been few instances of significant reclamation. In central London the MI6 development on the south bank of the river at Vauxhall Bridge is the largest in Central London and further down the river the extension of the Northfleet Hope container terminal at Tilbury for Tilbury Container Services. At present (late 2002) extensive studies are being carried out to examine the hydrodynamic, environmental and morphological impacts of a proposed development in Upper Sea Reach on the north side of the river at the Shellhaven.

Available data and potential data sources Data relating to each of the developments described is very different. The MI6 information is limited to a review of the impact of the works on the river morphology. The impact of the Tilbury Container Services berth extension on the river regime was subject to greater examination, which comprised a site survey (ADP current velocities) the use of a large physical model and a desk assessment. The works were completed last year but no monitoring programmes instigated. Changes to the riverbed morphology could be determined by comparison of pre and future bathymetric surveys.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 35 3.2 Sediment processes and morphology

3.2.1 Sediment movement At any moment in time the total volume of the suspended sediment in the Thames Estuary will depend upon a number of variable sources and the complex relationships that relates these sources. Thorn and Burt described the silt regime of the Thames Estuary (HR Wallingford 1978) that could be determined from the data then available. Whilst much of the reported findings remain valid they do not provide as full an explanation of the suspended solids sediment regime that is now essential to examine the water quality and environmental issues that will require attention. A contemporary data collection programme using state-of-the art technology and analysis programs is required to appropriately enhance the understanding of the suspended solids sediment regime.

Available data The principle source of data is the collection of suspended solid concentrations carried out as part of the Thames Barrier and associated works studies. Much of this data is now more than thirty years old and is probably not truly representative of the present day sediment movement within the Thames Estuary. Suspended solid concentrations recorded from the late 1960’s to early 1994 (HR Wallingford 1980, 1986, 1991 and 1994) provide evidence of the range and changes to the suspended solids concentration regime pre, during and post construction of the Thames Barrier and associated estuary flood defence works. The Environment Agency regularly collects water samples to determine the suspended solids concentrations. These samples are obtained near to the water surface and should only be used for near surface assessment. The suspended solids sediment action is going on in the water column much closer to the riverbed or, in the case of fluid mud, at the bed.

Data requirements Through depth river cross section profiles of the suspended solids regime can now be obtained using a technique based upon acoustic backscatter measurement (an example of which is shown in Figure 3.1 below). Data has been obtained at a few sites during the last year and provides a very different view of the suspended solids regime than was previously possible. There is a need for this technique to be used throughout the river to obtain a good understanding of the suspended sediment regime and hence assess the impacts of any change to that regime on the hydrodynamic and environmental regimes of the estuary.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 36 Figure 3.1 An example of acoustic backscatter measurement of suspended solids concentration and other associated parameters

To obtain adequate information to provide the appropriate information to the study programme an intensive programme of Acoustic Backscatter measurement of the suspended solids regime within the estuary should be carried out. This data can be used to assess the impact of many sediment-related issues including the morphological change that could occur with increased frequency of barrier closure.

3.2.2 Natural and anthropogenic change If it is assumed that, for whatever reasons, the Thames Estuary is currently in a state of equilibrium, it is reasonable to assume that if all anthropogenic activities in the Thames Estuary were suspended the Estuary would in the long-term form a new regime condition created entirely due to natural forces. In the medium-term there would be an ever changing balance between the forces that presently control the river regime and those that would exist once all of the anthropogenic controls had disappeared. The overall effects on the morphology of the Estuary would be difficult to accurately predict, but inevitably the bed levels at locations that require maintenance dredging would rise with possible consequential changes to the hydrodynamics of the Estuary.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 37 The influence of dredging Dredging affects the natural morphology of the Estuary by virtue of what it is trying to achieve - the removal of material from the bed of the estuary that has been deposited by hydrodynamic / sediment interactions.

The influence of disposal of dredged spoil Disposing of dredged spoil can affect the morphology of the Estuary should the disposal take place at an unsuitable site. Inappropriate onshore disposal, for example, could lead to bank-side accretion taking place or the partial re-suspension of the dredged material, while offshore disposal at the wrong location could lead to accretion in navigation channels or an increase in suspended sediments re-entering the Estuary. Thus, the disposal of dredged material should be considered carefully.

The influence of riverside development Over the last few centuries the morphology of the Thames Estuary has been subject to much change. This has been due to the considerable and varied demands put upon it by riparian activity, and in addition to any natural evolution of the estuary. Little overall control or co-ordination of the riparian activities was exercised until comparatively recently, which over the long-term makes it virtually impossible to determine which morphological effect was caused by what anthropogenic event. Large capital or maintenance dredging programmes, the discharge of polluted effluents, the construction of riverside developments are all examples of events which could have had a significant influence on the flow regime of the estuary. Since the late 1960's and early 1970's ever increasing legislation, restriction and investigation have ensured that the impact of any riverside development works has been acceptable to the hydrodynamic, and hence morphological, regime of the estuary. More recently the importance of individual environmental issues and the overall environmental function of the estuary have become an essential part of the examination of any development that include estuary works or works that could impact upon the estuary.

The influence of structures constructed in the tidal waterway The construction of any structure in a waterway will have an effect on the flow and hence potentially on the morphology of that waterway. The spatial and temporal extents of any morphological change being dependent on the design and size of the structure. It is now considered imperative that any structure be designed to have minimal effect on a waterway. There have only been two major structures constructed in the Thames Estuary over the last thirty years, the Thames Barrier being, probably, the most radical of these. Much research effort was employed prior to construction of the Barrier to ensure that minimal changes to the workings of the estuary as a whole would occur. Environmental issues were not as high on the agenda then as they are today. Any proposed major construction would be subject to stringent investigation to ensure that any changes to the morphology, or ecology, of the Estuary would be minimised.

Creeks and tributaries The creeks and other tributaries of the Thames Estuary play an important part in the overall morphology of the Estuary. They are suppliers into the Estuary of freshwater and suspended material. At their points of inflow into the Estuary they assist in the formation of the local hydrodynamic regime which in turn is a major controlling factor in sustaining the current morphology of the Estuary.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 38 3.2.3 Bathymetry Since its beginnings in the early part of the last century the Port of London Authority has made regular surveys of the Thames Estuary within its Limits of Authority using its own hydrographers. These surveys being carried out and made available, for and as navigational aids. For convenience, the Port of London Authority now divides the Thames Estuary into a number of chart areas (shown on Drawing 11) and regularly surveys each area, the frequency at which the surveys are made depends upon the main uses of the river in that area and the known stability, or instability, of the river in that area. Surveyed bathymetry is also supplied to the Hydrographic Office for updating Admiralty charts of the Thames. HR Wallingford has a large, but not complete collection of these charts on paper and Appendix D provides a guide to some of the information held.

Available data S The Port of London Authority hold an extensive database but much is now held on microfishe and not particularly easy to recover. S Environment Agency S Medway Ports Authority S Individual riparian operators S Admiralty S HR Wallingford has comparisons of riverbed levels post 1970 for much of the estuary between the Barrier and Canvey Island, the data being obtained as part of individual projects. Upriver of the Barrier several short stretches of the river have been similarly compared. Much of this data is project based and permission for its use will have to be obtained

Assessment programme To understand how the morphology of the river has changed over the years a comparison of the available data is necessary. Because the estuary environment was subjected to many artificial and often unquantifiable controls and actions detailed comparison should be limited to post 1970. After this data bed depths within the estuary were allowed to establish their natural depth far more than had been possible when large scale dredging maintenance campaigns and development works were taking place.

Data pre 1970 should not be exempt from the review, but it must only be used with caution and on the understanding that any identified “changes”, especially those of a local nature, may have been caused by unrecorded activity. Large maintenance or capital dredging campaigns must be reviewed as part of the assessment.

Requirements for further bathymetric data The deepening of the navigation channel up to Gallions Reach in the early part of the last century and the subsequent deepening of the channel from Gallions to Lower Pool and any information relating to bed level change following removal of bridges with narrow multi-arched spans or construction of new bridges requires assessment. This is necessary to establish how changes to bed levels can affect water levels, especially in the upper reaches of the tideway and beyond.

There is undoubtedly a large volume of historical bathymetric data relating to the Thames estuary available from the Port of London Authority from which localised

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 39 natural and anthropogenic changes can be determined. However, to complete the knowledge base regarding the Estuary as a whole the bathymetry of the in-flowing tributary system would be required in order to assess if any changes in these waterways have had, or are likely to have, on tidal levels.

3.3 The existing flood defence system

Defence against tidal flooding within the study area is provided by a system comprising tidal walls (both ‘hard’ steel or concrete and ‘soft’ earth embankments) barriers, gates, sluices and pumps. Details of the multitude of different elements making up the defence system are not readily available from a single source, but the major elements are shown in Drawing 04 and summarised within Table 3.8 below:

Table 3.8 Defence types comprising the Tidal Walls

Length of defences (km) Number of structures Steel Concrete / Earth Other / Frontager Sluices / sheet- masonry embank- unknown flood Pumps gravity Barriers piled gravity ments type gates outfalls Location walls walls North Bank Teddington – 16.6 43.7 8.5 40.6 - - 3 - Woolwich South Bank Teddington – 8.222.92.627.2---- Woolwich North Bank Woolwich to 8.2 3.7 6.8 12.6 22 - 10 3 Mar Dyke South Bank Woolwich to 4.56.44.56.34412 Dartford Creek North Bank Mar Dyke to 45.1 22.6 2.5 111 7 1 4 Leigh on Sea South bank Dartford Creek 25.5 13.5 - 70 2 39 - to Allhallows Total 184.8 58.5 89.2

The approximate construction costs (Trafford 1981) are summarised in Table 3.9. Unfortunately it has not been possible to identify maintenance and repair costs for the various scheme components. However, discussions with the Environment Agency Area Flood Defence Managers, together with a review of records of expenditure by relevant flood defences committees would provide a useful starting point for the estimation of such figures.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 40 Table 3.9 Approximate cost of existing tidal defences

System component Construction cost estimate (June 1980) Thames Barrier, Woolwich £ 410 million Other Barriers £ 34 million Dock Gates £ 8 million Sluices £ 3 million Tidal Walls £ 225 million

3.3.1 Design standards and levels The defences were designed and constructed in the 1970s and early 1980s to provide protection against what was estimated to be a 1:1000 year event in 2030. This level included allowances for falling land levels and rising sea levels, but there was an understanding that some of the defences (principally the earth embankments on the south bank which were expected to settle) would be reviewed about half way through the sixty year design life. The design levels also included an allowance for a reflected wave of 0.69m at the barrier reducing to zero in the outer estuary and are known as the ‘Dartford envelope’. Further allowance was made locally for freeboard (dependent on wave conditions) and settlement of the defences (particularly for the earth embankments). The standard of defence was relaxed at a number of locations (including Cliffe Marshes) where the agricultural land did not warrant the capital investment required and the topography is such that adjacent areas are not threatened.

Prior to completion of the barrier, defences in central London, were raised to provide interim protection against flooding. These interim levels are above the 1930 Statutory levels, but less than the estimated 1:1000 level without the Thames Barrier operating. In many cases these interim defences have remained in place to the present day, although the Thames Barrier now provides protection against tidal flooding.

Mathematical modelling of the waterlevels within the estuary has recently been re- evaluated (Halcrow 2002a and Halcrow 2002b). It is understood that there is a degree of scepticism within the Environment Agency with regard to the accuracy of these results, particularly in the upper reaches of the estuary.

3.3.2 Present condition of defences Existing information on the condition of the defences is fragmented with the different Environment Agency Regions adopting a variety of practices. It is anticipated that this will shortly be resolved with the introduction of the National Flood and Coast Defence Database (NFCDD), which has recently been set up and is presently being populated with data.

It is understood that the defences within the Thames Region are inspected on a rolling programme, but although some data was provided it did not include information such as defence cross-sections or structural inspections. Several studies appear to have been undertaken in the late 1990s on the condition and expected life of the defences including the Thames Barrier (see for example RKL-Arup, 1998 and Barlow Lyde & Gilbert 1998), but there is thought to be only limited information on other barriers or dock gates within the region. A framework for assessing and maintaining the London tidal defences was prepared by the Environment Agency in 1997 (Environment Agency 1997) which provides a useful background to the defences and programme for

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 41 embayments studies to 2002. This study provides an indicative estimate of maintenance and repair costs (within the Thames Region) as £10 million per year, of which £5 million might be contributed by private organisations.

EA Southern Region is understood to have commissioned a comprehensive survey of their tidal defences that was reported by Babtie (1995). This was extended and updated by Scott Wilson Kirkpatrick (2001) who produced a report and GIS ‘Flood Defence Management Asset Data Collection’. The latter report provides recommendations with a total estimated cost of approximately £3.5 million. Drawings and records of most of the Southern Region tidal defences (including the Dartford Creek Barrier) are understood to be held at the Leigh office. During a previous study the typical cross sections for many of the defences in this area were prepared from the ‘as constructed drawings’ which were found to be extensive, but not comprehensive.

Binnie and Partners (1994) undertook a review of the condition of the tidal defences within the Anglian Region that used a database to record defence properties and conditions. The report suggests that most of the defences are in a serviceable condition, but that some of the steel sheet pilling had settled appreciably. This was reported to be a particular problem on Canvey Island where it had resulted in a reduction of freeboard of up to 400mm. It is not known whether any further studies or work was undertaken as a result of the review and it is understood that the database was not passed to the Environment Agency although the results of a topographic survey have been obtained.

Due to the differences in assessment and reporting of defence conditions it is unlikely to be possible to obtain any useful overview of defence condition or residual life until the initial population of the NFCDD system has been completed. This is currently expected to be achieved at the end of the first quarter of 2003.

3.3.3 Operations and maintenance There is summary information on maintenance procedures within the Flood Defence Management Asset Data Collection report for the Southern region defences, but little information has been identified for Thames and Anglian regions. It is understood that established procedures are in place for the operation of the tidal barriers, but these have not been reviewed.

3.3.4 Relevant studies and priority actions A scoping report for the Thames Tidal Walls (West) study area was completed for the Southern Region of the Environment Agency in 2001 and arrangements are understood to be in place for studies of the following embayments:

S Dartford S Bermondsey S S City of London S Stratford Marsh S Westminster S Deptford

It is anticipated that these studies will significantly improve the flood risk mapping and assessment of defence conditions for the embayments, but the time-scale for completion of all embayments down river of the Woolwich Barrier is not known. Whilst limited information on expected maintenance and repair costs for the tidal defences is available

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 42 through the medium term plans these are not sufficiently detailed to allow a rigorous review.

3.4 Environmental responses

The study area includes a wide range of environmental areas and resources including many areas designated to be of national and international importance which are shown in Drawing 12.

The variety of habitats within the indicative floodplain is illustrated by Drawing 13 which shows relevant habitat data from the CEH Land Cover Map 2000.

There are also a large number of significant archaeological assets within the estuary. Many were identified during the Thames Archaeological Survey (which is expected to be finalised early in 2003) although this does not provide coverage of the outer estuary area. Scheduled ancient monuments and many of the assets identified within the Thames Archaeological Survey are shown in Drawing 14. Additional information is likely to be available from the Thames Estuary Partnership and Kent County Council (which is understood to have been developing a GIS of environmental assets).

3.5 Recommendations i It is strongly recommended that clarification / confirmation of the accuracy of the Ordnance Datum for each of the tidal water levelling locations is addressed as soon as possible. This recommendation is made because the uncertainty relating tidal water levels could lead to inaccurate or misinterpreted analysis of past and present tidal information ii It is recommended that additional water level monitoring locations are installed, especially up estuary of the barrier, to provide better coverage of the tidal propagation within the estuary. iii It is recommended that a programme of ADP current velocity, salinity and the suspended solids concentrations (using Acoustic backscatter) not dissimilar in extent to that carried out for the Thames Barrier and associated works study be undertaken to provide the new round of studies with data appropriate to the task. The programme should include current velocity measurements in the Outer Estuary and tidal water levels throughout the estuary. These data should be collected to a programme that will be based on spring and neap tide data for both high and average/low fluvial flows. iv While it is possible to predict local wave climates, it is recommended that a suitable series of wave measurements be undertaken to directly measure the variation in wave climate along the Estuary. This programme of work should include the measurement of the offshore directional wave climate and, simultaneously, the directional wave climates at a number of locations in the lower and middle Estuary. Records of meteorological conditions should also be made at each of the sites.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 43 v To understand how the morphology of the river has changed over the years a comparison of the appropriate available bathymetric data should be included. vi It is suggested that the NFCDD data be collated and entered for the whole of the estuary as a priority and that as soon as this information is available an initial appraisal residual life and priority maintenance actions be prepared. This may usefully include a review of previous studies and if possible the recovery of condition data for the defences within Anglian Region. vii The existing standard of service provided by the defences needs to be assessed in the light of the best available information. This is likely to be most appropriate after the elevations of water level gauges have been checked and pilot models of the estuary have been shown to be capable of representing water levels accurately. viii Information on past and programmed expenditure on the flood defences within the estuary should be obtained. Historical data may usefully be obtained from Annual Reports produced by Flood Defence committees and anticipated expenditure identified from Medium Term Plans and discussions with EA Area Flood Defence Managers.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 44 4. EXISTING MANAGEMENT FRAMEWORK

Management guidance has been produced for various parts of the estuary at a number of different levels. This guidance is summarised in the following sections.

4.1 High level multi-disciplinary guidance

Management policy and high level guidance for the estuary and adjacent areas has been produced by partnerships incorporating a wide range of interest groups.

4.1.1 Management Guidance for the Thames Estuary The Thames Estuary Partnership (TEP) is an umbrella body that was formed in 1993 to assist with the co-ordination of action and projects across the wide range of organisations and sectors involved on the estuary. The work of the TEP is guided by a Steering Group of key players from across the estuary including representatives of the following organisations.

S Anglian Water S Medway Council S Cleanaway S National Farmers Union S Cory Environmental S Port of London Authority* S English Nature* S Royal Society for the Protection of S Environment Agency* Birds S Essex County Council* S Southend Marine Activities Centre S Greater London Authority S Thames Explorer Trust S Kent County Council S Thames Water S London Tourist Board and Convention S Thurrock Council Bureau S University College London* * also represented on the management group

A smaller Management Group which oversees the work of the Partnership staff guides the day to day management of the TEP. The organisations represented on the management group are shown with an asterisk above.

The geographical area covered by the TEP extends from Tower Bridge to Shoeburyness and the Isle of Grain. The current documents (TEP 1999a, TEP 1999b and TEP 2001) were based on the ‘Thames Estuary Management Plan – a Draft for Consultation’ which was published in 1996. Although the TEP itself does not have any statutory duties or responsibilities it provides a useful forum for a range of organisations which do.

The TEP have adopted a system comprising of overarching ‘Guiding Principles’ and twelve ‘key themes’ of agriculture, air quality, biodiversity, commercial use, education and public awareness, fisheries, flood defence, historical and cultural resources, landscape character, recreation, waster and water.

4.1.2 Medway and Swale estuaries partnership The Medway and Swale Estuary Partnership (MSEP) covers the Medway and Swale Estuaries between Yantlet Creek on the Isle of Grain, Seasalter to the east and as far as Allington Lock on the Medway. The partnership produced a strategy in June 2000 (MSEP 2000) which identified the following key issues:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 45 1. Promoting sustainable development and Integrated Coastal Zone Management 2. Integrating land/water use and commercial/ leisure activity 3. Protecting and enhancing natural resources 4. Integrating agriculture, landscape and heritage management 5. Promoting sustainable tourism and recreational activities 6. Involving local communities

Flood defence spans a number of key issues, but the last section of the strategy identifies specific guidance and outputs related to flood defence. This guidance encourages the facilitation and support of “the development of integrated coastal defence strategies which recognise the value of preserving biodiversity while protecting cultural heritage, social and commercial resources.”

Similarly the outputs support the development of LEAPS, CHaMPS and Coastal Defence Strategy Plans which inform options for coastal defence works throughout the entire estuary. The investigation and facilitation of the development of GIS data to assist informed decision making within the dynamic estuarine environment is also encouraged.

The members of the Medway and Swale Estuary Partnership are:

S Canterbury City Council S Medway Yachting Association S English Nature S Rochester Oyster and Floating Fisheries S Environment Agency S Royal Society for the Protection of Birds S Lower Medway Internal Drainage Board S South East England Tourist Board S Kent County Council S Sport England S Kent Wildfowling and Conservation S Swale Borough Council Association S Thamesport S Kent and Essex Fisheries Committee S University of Greenwich S Medway Council S Medway Ports

4.1.3 Essex Estuaries Initiative The Essex Estuaries Initiative has developed a strategy for the Colne Estuary which was issued in 1999 and is updating the Blackwater Estuary management plan which was first published in 1996 (further information is available from www.essexestuaries.org.uk). Although the initiative has not yet produced comprehensive guidance for the whole area it covers between Shoeburyness and Jaywick it is understood that a draft management scheme is presently under preparation. The Initiative also provides a useful forum for coastal managers and other stakeholders within the area.

Members of the management group for the initiative include representatives from the following organisations:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 46 S Maldon District Council S Kent and Essex Sea Fisheries Committee S Tendring District Council S Port of London Authority S Essex County Council S Brightlingsea Harbour Commissioners S Chelmsford Borough Council S Crouch Harbour Authority S Colchester Borough Council S Maldon Harbour Improvement Commissioners S Rochford District Council S London Port Health Authority S Southend Borough Council S Department for the Environment Food and Rural S English Nature Affairs S Environment Agency S Ministry of Defence

4.2 Flood and coastal defence policy and strategy

A number of policy and strategic studies specifically related to flood and coast defence have been undertaken in and around the Thames Estuary. The geographic extents of many of the studies are shown in Drawing 15 and a brief description of each plan is provided below:

4.2.1 North Kent Coast Shoreline Management Plan North Kent Coast Shoreline Management Plan (Halcrow et al 1996) covers sediment sub-cells 4a and 4b between the mouth of Yanlet Creek on the Isle of Grain and Dover Harbour and is dated August 1996. The geographic limits of the plan within the Thames, Medway and Swale estuaries appears to be broadly consistent with the Schedule IV boundaries of the Coast Protection Act (1949). The study area is divided into process and management units, with the policies for the relevant areas summarised in the table below:

Table 4.1 North Kent Shoreline Management Policy

Unit Preferred Policy Process Unit 1 – Isle of Grain Management Unit 1A Yantlet Creek to Grain Village Hold the existing line Management Unit 1B Grain Village Hold the existing line Management Unit 1C Grain Village to Horseshoe Point Hold the existing line

Process Unit 2 – Sheppey West Management Unit 2A Point to Garrison Point Hold the existing line Management Unit 2B Garrison Point to Minster Hold the existing line Management Unit 2C Minster to Warden Point Do nothing

Process Unit 3 – Sheppey East Management Unit 3A Warden Point to Leysdown-on-Sea Hold the existing line Management Unit 3B Leysdown-on-Sea to Shell Ness Hold the existing line Management Unit 3C Shell Ness to Horse Sands Hold the existing line

Process Unit 4 – Graveney Marshes Management Unit 4A Faversham Creek to Seasalter Hold the existing line Management Unit 4B Seasalter to Whitstable Harbour Hold the existing line

It is not known whether there are any proposals for the Plan to be revised in the near future.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 47 4.2.2 Essex Shoreline Management Plan The Essex SMP (Mouchel 1997) covers the shoreline between Mardyke on the North Bank of the Thames and Lawford on the Stour. The study does not appear to have been constrained by the Schedule 4 boundaries of the Coast Protection Act, but covers the whole shoreline for which the commissioning consortium of operating authorities were responsible.

The policies for the relevant defences are summarised in Table 4.2 below:

Table 4.2 South Essex Shoreline Management Policy

Unit Preferred Policy Coastal Unit 1 – The Thames Management Unit 1a Mardyke to West Tilbury Marshes Management Unit 1b East Tilbury Marshes to Mucking Marshes Management Unit 1c Stanford-le-Hope to Holehaven Creek Hold the existing defence Management Unit 1d Fobbing, Vange, Pitsea and Bowers Marshes line in the long term Management Unit 1e Northwick to South Benfleet Management Unit 1f South Benfleet to Leigh-on-Sea Management Unit 1g Leigh on Sea to North Shoebury

Coastal Unit 2 –Maplin Sands Management Unit 2a Shoeburyness Ranges to Haven Point Hold the existing defence line in the long term Management Unit 2b Haven Gore to Foulness Hold the existing defence line in the long term

The plan identifies that the short term policy of hold the existing defence line for Coastal Unit 2 may need to be revised following further monitoring and studies. It also states that ‘managed set backs will only be undertaken where it can be demonstrated that this is the only sustainable defence policy and that it produces a more sustainable estuary morphology.’

The possibility of retreating the existing defence line in Management Unit 1b (East Tilbury Marshes to Mucking Marshes) is identified within the SMP but discounted from further consideration due to the costs that would be associated with moving the refuse tips.

4.2.3 Essex Seawalls Management Strategy The Essex Seawalls Management Strategy (Halcrow 1998) was produced for the Anglian Region of the Environment Agency in June 1998. The Strategy adopts the same coastal units as were used in the SMP but excludes Coastal Unit 1 (The Thames) on the instruction of the client as these defences were within their operational life and would be reassessed by the EA. Coastal Unit 2 was omitted as the defences were not the responsibility of the Environment Agency.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 48 4.2.4 Isle of Sheppey Strategy Plan The Isle of Sheppey Strategy Plan (SWK 1998) covers the area of the Isle of Sheppey at risk from flooding. It does not cover the cliffs at risk of coastal erosion or low-lying areas that are not adjacent to the coast. The strategy assess the effects of a full range of options from do nothing to improved defences and concludes that the preferred strategy is to provide a secondary defence (providing protection against a 1:200 year event) immediately to the south of the main urban areas of Sheerness and Queenborough.

The rural area to the south of this would be protected to a much lower standard and process studies are proposed to examine the impacts of improvements to the existing defences. The present value of the proposed works over the strategy life of 50 years is £22.6 million and the benefits are estimated to be £369 million over the same period. Maintenance expenditure at the time of the strategy preparation is understood to have been £400,000 per year. It is not known whether any schemes have been implemented as part of the strategy.

4.2.5 North Kent Coast Scoping Study The North Kent Coast Scoping Study (Babtie Brown and Root 2001) area extended from Yantlet Creek (on the Isle of Grain) to Swalecliffe and included the Swale and the Medway Estuary as far as Hoo Ness. The Scoping Study was intended to pave the way for flood defence strategy plans within the Medway Estuary and Swale.

The plan documents existing information and consultation with a range of organisations including the Medway and Swale Estuary Partnership. The study concludes that any flood defence strategy would be best developed for the Swale and Medway in combination, possibly incorporating the existing strategy for the Isle of Sheppey. The upstream boundary in the Medway was not considered appropriate and the Rochester Road Bridge was suggested as a possible alternative.

4.2.6 Thames Tidal Walls (West) Strategy Study - Scoping Report Thames Tidal Walls (West) Strategy Study - Scoping Report (HRW 2001) following completion of the scoping phase of the Thames Tidal Walls (West) Strategy Study. The original commission had been for a flood defence strategy between the Dartford Creek Barrier and the east of Gravesend. The study reviewed relevant data and information, but concluded that the original boundaries would not allow consideration of the full range of strategic options. It was proposed that the study boundaries be significantly extended to integrate with the Thames Tidal Embayments Studies and allow consideration of the northern bank. Studies to enable a fuller understanding of estuary processes and a framework in which a consistent strategy could be adopted for the whole estuary were also proposed.

4.2.7 London Tidal Defences Strategy Plan Issue 1 London Tidal Defences Strategy Plan (EA 1997) provides a methodology for the economic assessment of tidal defence schemes and a useful summary of the defences at the time. The plan area is defined as the 1:1000 year combined tidal and fluvial flooding envelope for the Thames and tidal tributaries between Teddington Weir and Mar Dyke / the River Darent.

The area is divided into 23 discrete ‘embayments’ each of which would be analysed as hydraulically independent flood cells, although it was recognised that interconnections

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 49 with, and the influence of, adjacent ‘embayments’ would also need to be considered. There were also plans for statutory and advisory flood defence levels, as well as barrier operating procedures to be reviewed and a strategy for London’s tidal defences up to 2100 to be prepared. A draft advisory note issued by TecnEcon regarding appraisal of the tidal embayments was appended to the report. It is understood that this was subsequently revised by both Halcrow and RKL-Arup with input from the EA and MAFF (now DEFRA).

4.3 National and regional guidance and policy

The legislation relevant to flood defences within the study area is described in Section 2.5.1. In addition to this, there are a number of relevant guidance and policy documents produced at a national, regional and local level.

4.3.1 Water Framework Directive DEFRA has recently published a second consultation paper (DEFRA 2002b) on implementation of the ‘Water Framework Directive’ as national legislation. The directive is principally concerned with environmental quality of water bodies and requires all inland and coastal waters to reach "good status" by 2015. It envisages that this will be achieved by establishing a river basin district structure within which demanding environmental objectives will be set, including ecological targets for surface waters.

The Environment Agency also published a consultation paper on some of the technical and scientific aspects of the Directive (Environment Agency 2002b) which includes a useful summary of the directive. A third consultation paper by DEFRA is planned for 2003 which will contain Government Responses to the consultation and details of implementation.

4.3.2 Government flood management guidance In 1993 MAFF (now DEFRA) and the Welsh Office published their “Strategy for Flood and Coastal Defence in England and Wales” (MAFF 1993). This publication identified the need to manage the shoreline or estuary from the perspective of physical processes rather than in accordance with the administrative boundaries of the coastal operating authorities. In May 1999 the Government announced interim high level targets for flood and coastal defence to secure the delivery of its flood and coastal defence aims and objectives, with more comprehensive targets announced in November 1999 (DEFRA 2002a). The high level targets set by the Government deal with the three key objectives to achieve the policy aims:

1. To encourage the use of adequate and cost effective flood warning systems.

2. To encourage the provision of adequate, economically, technically and environmentally sound and sustainable flood and coastal defence measures.

3. To discourage inappropriate development in areas at risk from flooding and coastal erosion.

In recognition of the need to manage the coastline in tandem with natural processes, a series of voluntary alliances have formed comprising local authorities, the Environment

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 50 Agency and other major local interest groups (in the Thames this has been formalised as the Thames Estuary Partnership). The alliances aim to establish integrated regional strategies within a strategic framework that accommodates the varying spatial and temporal scales within which an estuary develops and defence options perform to deliver the high level targets.

To enable management decisions to be taken within such a strategic framework, a hierarchy of Plans and Appraisals are required as illustrated in the figure below:

Large-scale plans (SMPs, CFMPs, ChaMPs etc)

Strategy Plans

Scheme design / appraisal reports

Figure 4.1 Hierarchy of plans (after MAFF 2001b)

Whilst specific guidance has been produced for Shoreline Management Plans (SMPs) and Catchment Flood Management Plans (CFMPs) there has been no dedicated guidance for estuaries, although the recent DEFRA (DEFRA 2001) guidance on Shoreline Management Plans does devote a couple of pages to estuaries. There are presently five volumes within the MAFF Flood and Coastal Defence Project Appraisal Guidance, which provide an overview to the process (MAFF 2001a) and advice relating to; strategic planning and appraisal (MAFF 2001b), economic appraisal (MAFF 1999) approaches to risk (MAFF 2000a) and environmental appraisal (MAFF 2000b). A sixth volume describing post project evaluation is currently being prepared. Whilst much of this guidance is directly relevant to flood risk management within the Thames Estuary there are a number of issues where the scale of the problem is outside that provided for within the guidance. For example, Table 4.3 summarises the indicative standard of protection provided within the volume on economic appraisal.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 51 Table 4.3 Indicative standards of protection (after MAFF 1999)

Fluvial Coastal / saline Typical description and indicative range of Return Annual Return Annual housing units (or equivalent) per km of shoreline period probability period probability (years) of failure (years) of failure Intensively developed urban areas. (≥50) 50-200 0.005-0.02 100-300 0.003-0.01 Less intensive urban areas with some high grade agricultural land and/or environmental assets of 25-100 0.01-0.04 50-200 0.005-0.02 international importance. (≥25 to <50) Large areas of high-grade agricultural land and/or environmental assets of national significance with 5-50 0.02-0.20 10-100 0.01-0.10 some properties also at risk, including caravans and temporary structures. (≥5 to <25) Mixed agricultural land with occasional properties at risk. May also apply to environmental assets of 1.25-10 0.1-0.8 2.5-20 0.05-0.40 local significance. (≥1.25 to <5) Low-grade agricultural land with isolated agricultural or seasonally occupied properties, or <2.5 >0.4 <5 >0.2 environmental assets at little risk from frequent inundation. (>0 to <1.25)

Whilst it should be recognised that these are only indicative standards and the final standard of service provided by any defences will be determine by cost – benefit analysis, it is worth noting that some of the defences within urban areas protect far more than the 50 properties per kilometre of defence in the table above. It is therefore likely that considerably greater standards of protection (perhaps of the order of 1:1000 year return period that the existing defences were designed for) will be justified by economic analysis. However, the standard of protection justified by discrete areas of agricultural land may not be as good as that provided in the original wall raising works at the time of construction of the Thames Barrier.

4.3.3 Environment Agency and other operating authorities The Environment Agency has a statutory obligation to exercise supervision over all matters related to flood defence under the Water Resources Act (1991). The Environment Act (1995) picks up on this and describes the Environment Agency’s supervisory duty stating that it includes "all matters relating to flood defence". Specifically the Environment Agency is involved in the following:

S condition of flood and coastal defences and critical ordinary watercourses S assessment of flood risk S achievement of high level targets S emergency response to flooding incidents S awareness of flood risk in the community S future development proposals that have potential impact on flood risk S regulation of others S application of conservation duty and environmental impact

The Government provided further detail regarding these issues was provided by the Government in it’s ‘Elaboration of the Environment Agency’s Flood Defence Supervisory Duty’ (DEFRA 2002a).

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 52 The Environment Agency is primarily responsible for sea defences and works on main rivers, but other operating authorities are also involved in providing defence from flooding:

S Internal Drainage Boards a have responsibilities for ordinary watercourses in areas known as Internal Drainage Districts S Local Authorities have responsibilities for ordinary watercourses that are not in an Internal Drainage District S Maritime Local Authorities have responsibilities for coast protection (prevention of coastal erosion) and may also undertake sea defence works.

The powers given to the operating authorities to carry out works are all permissive, which means they can choose either to carry out works or not at their discretion. No operating authority can be compelled to use their permissive powers. The Environment Agency regional boundaries, internal drainage boards and local authorities are shown in Drawings 05 and 06.

4.3.4 Planning Policy Guidance The Office of the Deputy Prime Minister issues national planning policy guidance. The most relevant documents are the Planning Policy Guidance Note 25: Development and Flood Risk (ODPM 2001a) and Planning Policy Guidance Note 20: Coastal Planning (DoE 1992).

PPG 25 explains how flood risk should be considered at all stages of the planning and development process in order to reduce future damage to property and loss of life. It recommends that a precautionary position should be adopted and climate change considered. The document promotes the consideration of flood risk on a catchment- wide basis and suggests that development should seek where possible to reduce and certainly not to increase flood risk.

The guidance recommends that flood plains are used for their natural purposes and are protected from inappropriate development and confirms that the Environment Agency has the lead role in providing advice on flood issues, at a strategic level and in relation to planning applications. It also states that developers should fund the provision and maintenance of flood defences that are required because of the development.

The planning responses proposed for different flood risk area is summarised in Table 4.4 reproduced from PPG 25 (ODPM 2001a).

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 53 Table 4.4 Planning response to sequential characterisation of flood risk

Flood Zone Appropriate Planning Response 1. Little or no risk Annual No constraints due to river, tidal or . probability of flooding: River, tidal & coastal <0.1% 2. Low to medium risk Suitable for most development. Annual probability of flooding: For this and higher-risk zones, flood risk assessment appropriate to the River 0.1-1.0% scale and nature of the development and the risk should be provided Tidal & coastal 0.1-0.5% with applications or at time of local plan allocation. Flood-resistant construction and suitable warning/evacuation procedures may be required depending on the flood risk assessment. Subject to operational requirements in terms of response times, these and the higher-risk zones below are generally not suitable for essential civil infrastructure, such as hospitals, fire stations, emergency depots etc. Where such infrastructure has to be, or is already, located in these areas, access must be guaranteed and they must be capable of remaining operational in times of emergency due to extreme flooding. 3. High risk (see note b) a. Developed areas Annual probability of flooding, These areas may be suitable for residential, commercial and industrial with defences where they exist: development provided the appropriate minimum standard of flood River 1.0% or greater defence (including suitable warning and evacuation procedures) can be Tidal & coastal 0.5% or greater maintained for the lifetime of the development (see paragraph 31 below), with preference being given to those areas already defended to that standard. In allocating or permitting sites for development, authorities should seek to avoid areas that will be needed, or have significant potential, for coastal managed realignment or washland creation as part of the overall flood defence strategy for coastal cells and river catchments.

b. Undeveloped & sparsely developed areas These areas are generally not suitable for residential, commercial and industrial development unless a particular location is essential, e.g. for navigation and water-based recreation uses, agriculture and essential transport and utilities infrastructure, and an alternative lower-risk location is not available. General-purpose housing or other development comprising residential or institutional accommodation should not normally be permitted. Residential uses should be limited to job-related accommodation (e.g. caretakers and operational staff). Caravan and camping sites should generally not be located in these areas. Where, exceptionally, development is permitted, it should be provided with the appropriate minimum standard of flood defence and should not impede flood flows or result in a net loss of flood-plain storage.

c. Functional flood plains These areas may be suitable for some recreation, sport, amenity and conservation uses (provided adequate warning and evacuation procedures are in place). Built development should be wholly exceptional and limited to essential transport and utilities infrastructure that has to be there. Such infrastructure should be designed and constructed so as to remain operational even at times of flood, to result in no net loss of flood-plain storage, not to impede water flows and not to increase flood risk elsewhere. There should be a presumption against the provision of camping and caravan sites.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 54 PPG 20 (DOE 1992) relates specifically to the coastline and whilst recognising that some activities (such as tourism, port development and waste water treatment) must be undertaken in coastal areas, it sets out the following key issues:

S conservation of the natural environment S development, particularly that which requires a coastal location S risks, including flooding, erosion and land instability S improving the environment, particularly of urbanised or despoiled coastlines

The document describes how the planning system can reconcile development requirements with the need to protect, conserve and, where appropriate, improve the coastal environment. This can be achieved through development plans and planning decisions which implement policies for the conservation and improvement of the coastal environment, acknowledging the special character of the coast.

4.3.5 Regional development plans and policies The regional development plan covering the study area is RPG9, which provides regional planning guidance for the south east. The eastern part of the study area, known as the ‘Thames Gateway’ is identified as “a regional and national priority for regeneration and growth with the potential to make a major contribution to the Region’s economy”. The Thames gateway area (which is shown on Drawing 18) extends from East London through North Kent and South Essex and is unique in having its own sub- regional planning guidance - RPG9a (DETR 1995). A recent review of this document (ODPM 2001b) recommended that it is updated but it is not known whether this has taken place. The River Thames also has specific regional planning guidance in the form of RPG 3b/9b (GOL 1997), however the London part of this may be superseded by the London Plan.

The draft London Plan (GLA 2002a) forms the basis of the future spatial development strategy for the Greater London Area with a consultation period until 30 September 2002. The plan anticipates London growing within its existing green belt to be a more dense, compact city. The plan also has an appendix devoted to the River Thames and London’s other water spaces –the ‘Blue Ribbon Network’. The document states that the water space is “not seen as merely a setting for development. Rather, the London Plan promotes the use of the water space. Types of sustainable use are many and varied but include water transport, water recreation, waterside open space, natural habitats and flood storage or protection.”

Much of the growth is expected to take place within the Thames Gateway area and the key drivers behind this development are a network of four organisations:

S The Thames Gateway Strategic Executive (TGSE) are based in the Office of the Deputy Prime Minister and provide a strategic overview to each of the partnership organisations. There have been no official publications by the TGSE, but the ‘Zones of change’ shown in Drawing 18 were provided through personal communication with members of the TGSE.

S The Thames Gateway London Partnership; a sub-regional alliance of thirteen local authorities, the Learning & Skills Council - London East, the Universities of East London, Queen Mary, Goldsmiths, Guildhall and Greenwich and the London

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 55 Development Agency working together with the private sector and local communities to deliver the economic, physical and social regeneration of the Thames Gateway in London. The Partnership has close links with business through London First, the South London Economic Development Alliance and East London Business Alliance, together with community groups through the London Thames Gateway Forum.

S Thames Gateway South Essex Thames Gateway is an extension of the original Thames Gateway to include more of Thurrock, part of Basildon (including Basildon New Town), the boroughs of Castle Point and Southend-on-Sea, and a small part of Rochford including London Southend Airport. The present partnership board includes representatives of Thurrock Council, Basildon District Council, Castle Point Borough Council, the East of England Development Agency, Essex County Council, Essex Economic Partnership Limited, Rochford District Council and Southend Borough Council.

S The Thames Gateway Kent Partnership champions the economic, social and environmental regeneration of Kent Thameside, Medway and Swale. Board members presently include representatives of Kent County Council, Medway Council, Gravesham Borough Council, Dartford Borough Council, Swale Borough Council, BBP Regeneration Ltd, Medway Ports, Hutchison Ports (UK) Ltd, Kent & Medway Health Authority, Land Securities Development, the Thames Gateway Parliamentary Group, NW Kent Community & Voluntary Service, South East England Development Agency, Government Office for the South East and the South East England Regional Assembly.

The proposed developments are described in section 5.3.

4.4 Environmental, habitat and biodiversity

4.4.1 Local Environment Agency Plans The Local Environment Agency Plans (LEAPs) have been replaced by Local Contributions which are intended to provide a framework for improving the environment of a particular catchment or Environment Agency Area. However, some parts of the LEAPs remain relevant to flood defence issues and a number of generic issues, identified from those LEAPS that have been made available for the study, are summarised below:

S Climate change: maintaining the standard of service provided by flood defences in the light of climate change and sea level rise.

S Increased development: this can increase the risk of flooding from surface water runoff and increased extreme flows within rivers. It may however provide opportunities for environmental improvements.

S Physical degradation of watercourses and their corridors: the flood defence maintenance programme can play a significant role in safeguarding existing habitat and improving degraded stretches. Similarly the production and implementation of WLMPs can be useful.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 56 S Public access to rivers and defences: defences can provide significant amenity value for recreation activities, but use needs to considered during design of such structures and properly regulated to ensure that the defences are not damaged.

S Flood levels and floodplain: present knowledge of flood levels and flood plain areas may not be sufficiently precise to encourage public confidence in the defence provided against flooding.

4.4.2 Local Contributions Local contributions for the Eastern Area of Anglian Region, Kent Area of Southern Region and South East Area of Thames Region are all directly relevant. The documents comprise a listing of targets relating to both national and local objectives and a description of how it is intended that they are achieved. Issues relating to flood defence within the three areas are largely limited to the national targets, which are summarised below:

Targets over the next five years

S 75% of residents in flood risk areas will take effective action to prepare for possible floods

S Improving the coverage of flood warning services to 77.5% of properties in flood- risk areas

S 50% of flood defence systems in urban areas will be in ‘good’ condition or better

S No more than 5% (and, by 2008, 3%) of flood defences in urban areas will be in a ‘poor’ condition or worse

S No inappropriate development inside floodplains

S Fewer properties at risk of flooding will be exposed to ‘high’ risks

Other national priorities include:

S Improving flood forecasting and flood warning services

S Ensuring consistent standards of flood defences for communities

S Adopting innovative solutions to reduce flood risks

S Meeting the challenges of climate change

4.4.3 Coastal Habitat Management Plans Coastal Habitat Management Plans (ChaMPs) are being prepared for two sites on the north and south banks of the estuary. A partial copy of the Essex Coast and Estuaries CHaMP Draft Report (Posford Haskoning 2002a), and a near complete copy of the North Kent Coast and Estuaries CHaMP Final Draft Report (Posford Haskoning 2002b) have been reviewed. The Essex Coast and Estuaries CHaMP includes the Colne Estuary, Blackwater Estuary, Dengie, Crouch and Roach Estuaries and continuing into

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 57 the Thames Estuary proper. The North Ken Coast and Estuaries CHaMP extends from Gravesend to Herne Bay, including the Medway and Swale Estuaries.

The CHaMPs are intended to quantify habitat change, (loss and gain), and recommend measures to prevent future losses which could have a direct impact on flood and coastal defences. They have a timescale of between 30-100 years and will include strategic habitat monitoring programmes to map future changes. The CHaMPs are expected to inform and influence other coastal plans including SMPs, flood and coast defence strategies and those relating to estuary management.

The CHaMP set out the significance of the European designations and outlines the conservation objectives for management as well as predicting likely shoreline change over the next 30-100 years (based on a review of coastal process information, strategic plans for flood and coastal defences, available data and expert opinion). The North Kent document predicts changes to the designated habitats that could have a detrimental impact on the designated features of the international sites, largely through a predicted shift from intertidal mudflat to saltmarsh habitat. This would in turn reduce available feeding area for wintering waterfowl populations, notably mudflat specialists, but could also be viewed as an ecological benefit given extensive predicted losses elsewhere in southeast England. The section of the report detailing management actions to mitigate the detrimental changes to international sites was not included in the draft reviewed.

4.4.4 Water Level Management Plans Water Level Management Plans (WLMPs) are written statements of the water level management objectives for a given area. They consider the water level requirements for a range of activities, including agriculture, flood defence and conservation, and how these can be balanced and integrated.

WLMPs are prepared by the Environment Agency, Internal Drainage Boards and certain local authorities. Priority is given to preparing plans for Sites of Special Scientific Interest (SSSIs), i.e. sites of national nature conservation importance. The main requirement for these sites is to maintain or rehabilitate their designated interest. Water level management plans are known to have been produced for a number of parts of the study area, and those obtained to-date are summarised in Table 4.5.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 58 Table 4.5 Summary of Water Level Management Plans

Area Participating organisations Summary Recommendations South Thames Environment Agency Maintain waterlevels and in places raise Estuaries and English Nature waterlevels, to restore and maintain the Marshes SSSI RSPB wildlife interest of the SSSI whilst balancing (Binnie Black the need to provide landowners with adequate and Veatch water for livestock farming and acceptable 1998) standards of Flood Defence and Land Drainage. Dartford Environment Agency The development of a drainage regime that Marshes Groundwork Kent Thames- raises water levels and conserves / enhances (GKT-s 2002) side the biodiversity of the plan area balanced with Glaxo-Smith-Kline the needs of the landowners and recreational Dartford BC interests. University of Greenwich It should be noted that there are significant gaps in the information available to inform this plan but that this need not hinder the progress of improved water level management on Dartford Marshes. Vange & Environment Agency S Maintain the status quo at Fobbing Marsh Fobbing English Nature with respect to water level management Marshes FRCA whilst seeking environmental (EA 1999a) Essex CC enhancements Basildon District Council S Seek environmental enhancements Thurrock Borough Council through the management of waterlevels at Essex Wildlife Trust Vange Marsh S Install gauge boards within the Fobbing Marsh section of the WLMP area Benfleet and Environment Agency S Seek environmental enhancements Southend English Nature through changes to the management of Marshes SSI FRCA water levels and Hadleigh Essex CC S Installation of structures within the plan Marshes Castle Point BC area (EA 1998) Southend on Sea BC S Encourage the upgrading of land within Railtrack the ESA Tier 1 scheme to Wet Tiers Leigh on Sea Wildfowlers Assn. Pitsea Marsh Environment Agency S Maintain the status quo with respect to (EA 1999b) English Nature water level management whilst seeking Essex CC environmental enhancements FRCA S Support the development of the existing Basildon DC scrape on land adjacent to the WLMP area Essex Wildlife Trust S To encourage more land into appropriate agricultural management to allow entry into the ESA scheme

4.4.5 Tidal Thames Habitat Action Plan The Tidal Thames Habitat Action Plan (TEP 2002) provides the London component of the wider Tidal Thames Habitat Action Plan to guide the work of the London Biodiversity Partnership. It includes a description of the key habitats on the Tidal Thames in London including those settled on Flood Embankments, Flood Walls and Tidal Creeks. The report also identifies objectives, targets and actions of which those most relevant to flood defence are summarised below:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 59 S Objective 1: Ensure that strategic plans and initiatives recognise the biodiversity importance of the Tidal Thames. Target: Full consideration of Tidal Thames biodiversity in the ‘Blue Ribbon’ concept of the London Plan by 2003. Ensure the Biodiversity Action Group is established as a mechanism for scoping on all major developments and strategic initiatives including the Tideway Strategy, Planning for Flood Risk Management Project and Thames Landscape Strategy.

S Objective 3: To create new areas of riverine habitat. Target: Create five new areas of habitat in London by 2005. Identify and promote opportunities for new environmental approaches to flood defence design.

4.4.6 Futurecoast The Futurecoast study was commissioned by DEFRA in order to help guide the next round of SMPs. The study provides a sound, scientific and nationally-consistent basis for predicting coastal change in England and Wales over the next 100 years based on data relating to coastal processes and geomorphology. The study has considered fresh approaches to assessing shoreline evolution and draws on existing information and experience.

Futurecoast only covers that part of the coastline for which SMPs have been prepared (which excludes estuaries). The boundary within the Thames Estuary is Mardyke on the north bank and Yantlet Creek on the Isle of Grain on the south bank. However, there is data for the outer estuary that can feed into the flood risk plan for the Thames Estuary especially in relation to the modelling that will be required. The framework developed for consistent reporting, assimilation and presentation of the SMPs may also be applicable to decisions regarding the estuary and this will require further investigation during future studies.

4.4.7 Other relevant plans The Thames Oil Spill Clearance Association (TOSCA), which is managed by the PLA in conjunction with oil companies operating on the Thames, has undertaken the identification of sensitive habitats for oil spill contingency planning (TOSCA 2002). This information is presently available in paper form, but would make a significant contribution to any baseline environmental survey of the study area. It is understood that the partnership provides a dedicated service to respond to oil spills occurring in the tidal Thames between Tower Bridge and Sea Reach No. 1 buoy and it is thought that the habitats reviewed are limited to this area.

4.5 Recommendations i Liaison with TEP, MSEP, Essex Estuaries Initiaive and other interested organisations should be maintained to facilitate a continued understanding of their work and consultation on flood management within the Thames Estuary when appropriate. ii The Thames Estuary Flood Risk Management team should undertake continued liaison with ongoing and any future flood defence or water management studies with a view to establishing appropriate and consistent boundaries.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 60 iii Discussions should be held with organisations responsible for developing national, regional and local policy and a programme of consultation organised to ensure that interested individuals and organisations are kept informed of progress and can contribute to the flood risk management plan. Developments in research and technology should also be monitored.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 61 5. IDENTIFICATION OF ASSETS AT RISK FROM FLOODING

5.1 Topography and ‘flood cells’

The indicative tidal flood plain within the study area has been divided into a series of flood cells based on the topography (shown in Drawing 16) and natural features (rivers, catchment boundaries etc) of the area. Within the Thames Region these were based on the ‘embayments’ which were defined within the ‘London Tidal Defences Strategy Plan (Environment Agency 1997). Whilst it is understood that studies are presently ongoing into the defences for each ‘embayment’ no additional information was available for inclusion within this report. The flood cells identified within the Thames Tidal Walls Scoping Report were also adopted and in other areas new flood cell boundaries were developed. The location and extent of each of the flood cells is shown in Drawing 17 and the flood cells are listed below:

Original Thames Region Embayments Proposed New Embayments 1. Barking & Dagenham 24. Foulness Island 2. Royal Docks 25. Potton Island 3. Roding West Bank 26. Southend 4. Stratford (east bank of River Lee) 27. Canvey Island 5. Poplar (west bank of River Lee) 28. Bowers Marshes 6. Isle of Dogs 29. Fobbing Marshes 7. City of London 30. Mucking 8. Westminster 31. East Tilbury 9. Hammersmith & Fulham 32. West Tilbury 10. Chiswick 33. West Thurrock Marshes 11. Isleworth 34. The Swale 12. Twickenham & Teddington 35. Isle of Sheppey 13. Dartford (West Bank River 36. Chetney Marshes 14. Thamesmead 37. Chatham 15. Greenwich 38. Isle of Grain 16. Deptford Creek East 39. North Kent Marshes 17. Bermondsey 40. Shorne Marshes 18. Clapham 41. North Fleet 19. Wandsworth 42. Swanscombe Marshes 20. Barnes 43. Dartford & Stone Marshes 21. Mortlake 22. Kew 23. Richmond

It should be noted that these have been developed on the basis of the relatively limited information reviewed during the study to date. However, they are thought to provide an appropriate initial starting point from which the relative importance of the defences can be assessed. The extent to which each flood cell is hydraulically discrete has not been fully assessed, and in some locations (notably Southend) several flood cells which are almost certainly discrete have been allocated to a single embayment to avoid excessive numbers of small flood cells.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 62 5.2 Review of assets at risk from flooding

5.2.1 ‘National assets at risk from flooding and Coastal Erosion including the potential impact of climate change’ The most recently published report ‘National Appraisal of Assets at Risk from Flooding and Coastal Erosion, including the potential impact of climate change’ (Halcrow 2001) estimates that nationally over 1.8 million residences and 140,000 commercial properties are at risk from flooding. The capital value of these properties was estimated to be £222 billion with approximately £110 billion lying within Thames Region. Unfortunately a breakdown for the study area is not available within this report, but a comparable value has been estimated within section 5.2.2.

At the time of writing the study is being updated using a more accurate method of calculating potential damages and benefits and a new comprehensive estimate of national assets at risk from flooding is expected to be produced. Whilst the study will not report a discrete value for the Thames Estuary it is expected that a similar methodology could be applied to the study area relatively quickly.

5.2.2 Assets within the study area Analysis of the flood cells identified within section 5.1 provides a useful extension of the information presented in the National Assets at Risk Report. An initial review utilised ADDRESSPOINT data to determine property numbers and census data for population within each of the flood cells and together with significant infrastructure this is summarised in the table below:

Table 5.1 Distribution of assets within the different flood risk compartments

Approx. Approx. Number of Properties area of length of properties Other typical key Flood Cell Population per km of flood cell defences within IFP assets within IFP defence (km2) (km) (000s) Power station + 2 Barking & 1 31 18 27.4 hospitals + 2 53,971 1489 Dagenham landfill sites City Airport + 2 2 Royal Docks 19 14 41.9 hospitals + STW + 82,451 3046 landfill site Roding West 3 3 6 5.9 Landfill site 15,004 926 Bank Stratford (East 4 2 4 3.3 5,185 822 Bank River Lee) Poplar (West 5 3 10 10.6 16,410 1044 Bank River Lee) 6 Isle of Dogs 3 7 11.8 12,981 1805 7 City of London 2 14 8.6 10,429 613 Railway station + 2 8 Westminster 3 8 21.1 32,584 2702 hospitals Hammersmith & 9 17 11 83.2 2 hospitals 167,120 7860 Fulham 10 Chiswick 4 10 8.5 1 hospital 18,519 851 11 Isleworth 2 8 31.7 1 hospital 6,700 4084

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 63 Table 5.1 (contd.)

Approx. Approx. Number of Properties area of length of properties Other typical key Flood Cell Population per km of flood cell defences within IFP assets within IFP defence (km2) (km) (000s) Twickenham & 12 3 11 6.8 13,212 601 Teddington Dartford (West Industrial estate + 2 13 372.9 4,407 388 Bank River landfill sites Power station + 14 Thamesmead 16 12 24.6 STW + 2 landfill 48,354 2062 sites 15 Greenwich 7 9 5.4 1 hospital 9,161 574 Deptford Creek 16 0 2 1.5 2,281 632 East Heliport + 2 17 Bermondsey 28 23 141.6 railway stations + 2 242,305 6105 hospitals 18 Clapham 1 1 2.0 2,645 1561 19 Wandsworth 1 2 3.4 4,986 1554 20 Barnes 4 7 8.9 1 hospital 17,007 1308 21 Mortlake 1 2 4.9 7,634 2796 22 Kew 5 8 10.6 19,582 1253 23 Richmond 1 7 0.4 810 57 24 Foulness Island 28 0 0.1 0 - 25 Potton Island 4 0 0.0 0 - 26 Southend 13 6 4.3 8,913 703 27 Canvey Island 15 22 15.1 36,387 679 28 Bowers Marshes 8 3 0.0 Landfill site 0 4 29 Fobbing Marshes 15 11 0.0 Industrial estate 0 3 30 Mucking 0 1 0.0 Landfill site 0 44 31 East Tilbury 4 6 1.1 2 landfill sites 2,937 190 Power station + 32 West Tilbury 14 10 6.4 15,606 655 landfill site West Thurrock 33 7 9 3.3 Power station 4,165 378 Marshes 34 The Swale 39 - 1.5 5,847 - 35 Isle of Sheppey 53 - 8.5 2 landfill sites 18,437 - 36 Chetney Marshes 17 - 2.0 Landfill site 3,508 - 37 Chatham 20 - 5.3 6,948 - 2 power stations + 38 Isle of Grain 23 - 0.7 700 - 3 landfill sites North Kent 39 27 17 0.1 Landfill site 0 6 Marshes 1 hospital + landfill 40 Shorne Marshes 12 9 2.2 2,712 229 site 41 North Fleet 1 2 0.0 Power station 632 5 Swanscombe 2 Industrial estates 42 360.3 909 45 Marshes + 2 landfill sites Power station + Dartford & Stone 43 861.0industrial estate + 2,609 181 Marshes hospital + STW Teddington – Leigh on Sea / 266 295 494 Allhallows Whole area 468 - 519

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 64 The total capital value of the properties within the indicative flood plain can be estimated using a nominal value of £200,000 per property - approximately the average between property prices within Greater London and South East England as of 31 July 2002 (Land Registry 2002) this would give a total value in excess of £99,000 million.

When other assets which cannot be readily quantified in monetary terms (such as environmental areas, archaeological features, social disruption and anxiety) are also considered it is apparent that there is considerable justification for developing a comprehensive strategy for flood management within the area.

5.3 Future change scenarios

Large parts of the study area are undergoing rapid changes as a result both of both the construction of the Channel Tunnel Rail Link and having been identified for development to accommodate the expansion of London. The Thames Gateway provides a framework for much of this development within the study area. As can be seen from Drawing 18 fourteen zones of change have been identified within the Thames Gateway area and although the pattern and scale of development is different for each zone, many are located within the Indicative Flood Plain and will significantly increase the assets at risk from flooding.

Recent forecasts by the Thames Gateway Strategic Executive for developments within the zones of change up to 2016 are summarised in Table 5.2 below. The table also shows the approximate proportion of each zone within the Indicative Flood Plain.

Table 5.2 Proposed development within the Thames Gateway ‘Zones of Change’

Growth Forecast 2001-2016 Approx. % in Zone (approximate area – km2) Indicative Housing Employment Flood Plain 1 Isle of Dogs (3) 3,500 105,000 100 2 Deptford / Lewisham / Greenwich (3) 1,000 5,500 40 3 Stratford / Leaside Royals (20) 16,800 51,000 90 4 and East 7,000 15,000 95 Greenwich (3) 5 Woolwich / Belvedere / Erith (13) 5,400 12,500 95 6 Barking / Havering Riverside (11) 8,000 4,200 95 7 Kent Thames-Side (37) 30,000 50,000 45 8 Medway (35) 6,300 12,000 45 9 Grain (7) 3,700 7,000 80 10 Sittingbourne / Sheerness (23) 4,150 12,500 70 11 Thurrock Riverside (27) 3,500 8,500 50 12 Basildon (23) 1,300 5,300 5 13 Canvey / Shell Haven (17) 2,400 10,000 80 14 Southend (30) 1,000 9,500 15 Total (253) 94,050 308,000

It should be noted that the analysis has been based on the information provided by the Thames Gateway Strategic Executive. The definition of the zones of change has not

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 65 been precisely determined and the values tabulated above are only approximate, however further analysis using more detailed information is unlikely to lead to significantly different conclusions.

If it is assumed that the housing and employment growth for each zone are uniformly distributed it is possible to estimate the scale of development within the indicative flood plain. It is thus found that whilst only just over half of the plan area for the zones of change is in the indicative flood plain this will contain approximately 69% of the housing growth and 77% of the employment growth.

The expected increase in the density of development within other areas parts of the study area (much of which is expected to take place close to the various bodies of water GLA 2002a) is also expected to lead to a further increase the assets at risk of flooding.

5.4 Definition of proposed valuation methodology for each asset type

Standard methodologies for quantifying flood damages to buildings are provided by the ‘Middlesex Manuals’ which are presently being updated to a new ‘multi-colour manual’. However, the following will also need to be considered:

S Road and rail traffic disruption S Agricultural production S Environmental gains and losses S Social and civic amenities S Recreational areas S Landscape and visual impact

These must be dealt with by alternative methods such as the provision of additional resources or mitigation measures. It is important that the impact of flooding and flood defence options on these assets and issues is thoroughly considered and included in the decision making process. The processes by which this can be done, and the data required, are summarised in the following sections.

5.5 Review of data for use in assessing economic impacts of flooding

The appraisal of economic impacts from flooding is well described within the DEFRA FCDPAG3: Economic Appraisal (MAFF 2000). The methodology described within this document can be adapted to different levels of analysis and is being further developed within the research project ‘Risk Assessment of Flood and Coastal Defence for Strategic Planning’ (RASP). RASP provides a hierarchy of three levels of analysis (high, intermediate and detailed) which are described in detail on the project website (www.rasp-project.net) and summarised below:

S High Level Method. This is based on nationally available datasets on flood defences, flood plains and land use. It will provide a methodology for updating national estimates of flood risk and enable changes in flood risk in England and Wales to be monitored and reviewed.

S Intermediate Level Method. This will use measurements or model estimates of flood water levels, flood defence levels and ground elevation to generate better

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 66 estimates of flood risk. It will be used to inform strategic decisions on flood risk management.

S Detailed Level Method. This will use detailed information about the composition of defences to generate an improved estimate of their probability of failure by a number of different failure modes. Simulation methods will be used to estimate risks in a large number of flooding scenarios.

It is expected that the analysis presented within this report could be readily extended to provide the high level analysis of the whole estuary used to identify flood risk and economic damages within the estuary as a whole.

The intermediate level will need inputs such as water levels from pilot model and other studies to accurately quantify the potential flood damages and assess the benefits of large scale options (such as major structures or managed realignment) on the estuary as a whole.

Detailed analysis will be needed to fine tune strategy or scheme options to provide the most appropriate defence. Whilst the three levels of analysis will work at different levels of detail they will use a consistent set of base data to ensure that the results are both accurate and coherent. This base data is discussed in the following sections.

5.5.1 Topography National topographic datasets include OS PANORAMA (used to produce Drawing 16) and OS PROFILE, which are based on the same source data and provide an accuracy of the order of M 1.5m. It is understood that these will shortly be supplemented by the NEXTMap Britain data set which will provide an improved accuracy of M 0.5m over populous and flood-prone areas. This is considered sufficient for the high level analysis but will be verified or supplemented by more detailed photogrammetric and LIDAR topography where this is available (present coverage is shown in Drawing 19) for the intermediate and detailed analysis.

5.5.2 Flood risk mapping The Environment Agency Indicative flood risk mapping is shown in Drawing 01 and superimposed on the topography in Drawing 16. The tidal outline is understood to represent the expected area affected by a 1:1000 year tidal flood event and has been created using relatively crude data that displays some inconsistencies with the panorama data used for the topography in Drawing 16 (which is similarly crude).

The flood risk outlines may be used as the basis of the inland study boundaries and it is understand there will be two new sources of flood outlines for the estuary in the coming months:

1. Section 105 flood outlines. Developed as part of the embayments studies within Thames Region, and on a piecemeal basis for areas within the Southern and Anglian Regions, these will include outlines representing the 1:10year, 1:100 year, and 1:1000 year flood events based on OS PROFILE data and Photogrammetry / LiDAR data wherever this was available. The flood modelling techniques and source of extreme waterlevels are not known.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 67 2. The National Extreme flood outlines. These are being produced as part of a national initiative using the NEXTMap Britain data set and will identify the 1:200 year and 1:1000 year flood outlines.

The results of these exercises will be highly dependent on accurate predictions of extreme waterlevels as well as the topographic representation of the flood risk area. There may be merit in repeating the studies to refine the study boundaries if results from pilot modelling of extreme waterlevels in the estuary are significantly different from those used in the flood risk mapping.

5.5.3 Property details The number and location of properties within the study area can be readily determined from the OS ADDRESSPOINT database. Capital or ‘write off’ values can be estimated for residential properties using data from the Land Registry or www.proviser.com and for commercial properties based on their rateable value. The FOCUS database can be used with ADDRESSPOINT to allow recurrent flood damages to be estimated for commercial properties although large properties will need to be assessed on a case by case basis.

5.5.4 Defence characteristics Defence characteristics are expected to be available from the National Flood and Coast Defence Database (NFCDD) which should be fully populated by the end of the first quarter of 2003. This information is likely to need supplementing (for example with details of the defence cross section) before it can be used in the detailed analysis but should be adequate for the high level work.

The detailed analysis will likely include categorisation of defences into a number of types for which failure mechanisms are determined. Examples of such failure mechanisms are provided below:

S Flow or wave overtopping of the defence. During an extreme water level event, it is possible that the level of the Thames within the study area would exceed that of the defences and overtopping would occur. Similarly if less extreme water levels coincided with significant winds from certain directions it is possible that wave overtopping could lead to flooding.

S Structural failure of the defences. The present defences were constructed some time ago and although maintained, each will have a certain probability of failure. This may be caused by persistent erosion of the riverbed adjacent to the defence leading to instability, corrosion of a sheet steel pile or tie rod, or other developments immediately behind the defence resulting in an excessive loading. Structural failure may be expected to occur during an extreme event when the defences are under increased loading, and as a result, could result in catastrophic failure and considerable flooding. The likely residual life of the defences and possibility of structural failure can be assessed for each type of defence based on a series of generic trees fault and the results of this applied within the assessment of economic loss.

S Seepage under the defences. Depending on the dimensions of the defences and the properties of the underlying soil it is possible that, during an extreme event, the head of water within the River Thames would result in seepage of water underneath the

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 68 defences and into the area behind the defences. Such seepage may cause flooding directly, but might also be expected to result in piping at the rear toe of soft defences. This could destabilise the rear face and possibly result in catastrophic failure. It is understood that drains to relieve pressure were provided on some defences but may now have become blocked.

S Blockage or failure of and outfall or flap valve. Blockage of an outfall or flap valve may result in the build-up of water behind the defences, depending on the nature of the outfall, the topography of the land and the duration of the blockage this may result in significant flooding. The failure of a flap valve could potentially be worse, resulting in a flow of water into the defended area at high water or during an extreme event. The result of this would also vary with location, but could be significant.

S Mechanical or electrical plant failure. A number of elements of the flood defences system are primarily operated by mechanical and / or electrical equipment. It is understood some backup or alternative arrangements have been made for operation of such defences, but nevertheless there remains a possibility that there will be a delay or failure to operate some or all of these defences. This could result in extensive damage if, for example, a number of flood gates were left open or the Woolwich Barrier failed to operate properly during an extreme event.

S Tide locking. Many of the areas behind the defences drain by gravity, through flap valves to the Thames. The effect of a prolonged high water level within the Thames Estuary would be to prevent drainage through the flap valves. If this coincided with a prolonged period of heavy rain it could result in a build up of water to landward of the defences. The effects of this would be minimised by pumping stations and balancing ponds, but could be significant.

5.6 Recommendations i The 43 flood cells should be reviewed and revised as improved topographic and flood level information becomes available. ii It is recommended that the assets at risk of flooding should be reviewed and updated using an appropriate methodology as improved information and techniques become available. iii Liaison with the Thames Gateway Strategic Executive should be maintained and discussions (also including other relevant organisations) held to develop an approach to flood management for the proposed developments. iv Progress of the NFCDD should be kept under review and arrangements put in place for the collection or collation of additional information enabling characterisation of existing and future defence performance.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 69 6. STUDY BOUNDARIES

The temporal and spatial boundaries for the estuary management plan will need to reflect the aims and objectives of the plan. In general terms they will need to ensure that ‘all major processes, impacts and consequences’ (MAFF 2001) of the policy are captured within the area considered.

Recent DEFRA guidance (2001) suggests that “estuary processes should be integrated within SMPs as fully as possible; this will generally be up to the tidal limit”. The document goes on to suggest that policies will usually be selected up to the existing schedule IV boundary and the upstream boundary should be consistent with any river management plan boundaries.

In considering the spatial study boundaries it is apparent that the boundaries for the process studies providing an understanding of estuary development and response will need to be considerably wider than the boundaries for which options are developed. Thus the temporal and spatial boundaries for management / intervention and physical process understanding / option evaluation are assessed separately below.

6.1 Temporal

There are likely to be two temporal scales for the development of the flood defence strategy - the first will be concerned with short term actions required to maintain the integrity of the existing defences and will probably be limited to 5 years, following which the main strategy will be implemented.

Strategies are usually considered over a 50 year timescale for three reasons (MAFF 2001b):

S Physical and social predictions are difficult over a longer period

S The effect of discounting on costs and benefits streams beyond 50 years renders them unlikely to have a significant impact on decisions

S Policies that are shown to be sustainable over 50 years are likely to be sustainable in the longer term.

However there are a number of reasons for the consideration of a longer period for the Thames Estuary:

S The size and significance of the assets protected within the estuary make it essential that the strategy is sustainable in the longer term

S The cost of the assets required to provide an appropriate standard of defence are likely to be very large and the sensitivity to the use of lower discount rates may be significant

S The condition and design of some elements of the existing flood defence system is such that it may be possible to extend their service life considerably beyond 50 years.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 70 The accuracy with which scenarios can be predicted and relevant models run will be reduced for long term planning horizons (such as 100 years suggested above). However, by undertaking simulations for a range of different scenarios it will be possible to produce relevant information to inform the strategy development.

6.2 Management / intervention

When considering management and intervention options for the estuary it will be important that the boundaries provide scope the whole range of options, including new barriers or barrages and defence re-alignment, to be assessed throughout the estuary. Similarly it is important that the area is sufficiently large to account for the loss or gain of habitat within the plan.

There are a number of other issues to consider when determining study appropriate management / intervention boundaries which are discussed in the following sections.

6.2.1 Existing Management Policy As described in Section 4 the existing Thames Estuary Partnership study area runs from Tower Bridge to Shoeburyness and the Isle of Grain. The complementary Partnerships for the Swale and Medway Estuary and the Essex Estuaries Initiative start at the Shoeburyness – Isle of Grain Boundary and extend to Jaywick and Seasalter.

The Shoreline Management Plans for the north and south banks extend rather different distances into the estuary with the Essex SMP going as far as MarDyke and the North Kent SMP stopping at Yantlet Creek. The North Kent Scoping Study also adopted Yantlet Creek as the Western boundary.

6.2.2 River management and catchment studies The Medway catchment forms one of the sites for the pilot Catchment Flood Management Plans (CFMPs) and it is understood that the downstream boundary is at the normal tidal limit at Allington Lock (Babtie Brown and Root 2002). However, it is believed that future CFMPs within the Thames River Basin District likely to extend to the confluence with the Thames itself.

It is also understood that a flood defence strategy for the Medway and Swale Estuaries is under preparation, and it is assumed that this will cover the whole of the Swale and Medway Estuary Partnership area.

6.2.3 Other relevant Boundaries Schedule 4 of the Coast Protection Act (1949) defines boundaries between estuaries and the open coast and these are understood to run between the Southend / Basildon Administrative Boundary on the North Bank to Allhallows on the South Bank. Similarly Schedule 4 boundaries run across the mouth of the Medway estuary (between Grain and Sheerness) and the Swale.

The Water Framework Directive requires the country to be divided into a series of River Basin Districts based on catchments. Although these are not yet finalised draft boundaries have been obtained and are shown in Drawing 20. It is understood to have been proposed that the estuarine boundaries will be co-incident with those for the Urban Waste Water Treatment Directive which in turn was based on those for the 1960 Clean

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 71 Rivers (Estuaries and Tidal Waters) Act and these are also shown in Drawing 20. It is notable that the estuarine boundaries are not continuous with the River Basin boundaries.

6.2.4 Flood cells and flood risk areas In determining limits for consideration of management or intervention options it is prudent to avoid a continuos flood risk area (flood cell) spanning the boundary as this would require a high degree of interaction between adjacent studies and could result in double counting of damages or benefits.

6.3 Physical Processes / Understanding

It is likely that the physical process boundaries for the investigation of physical will be related to similar levels of detail as are used in RASP (i.e. high, intermediate and detailed). Initial proposals for these boundaries are summarised below, but provision should be made to modify them in the light of new data and the results of any pilot modelling.

6.3.1 High Level A high level modelling framework to provide the boundary conditions to more detailed studies and provide insight as to the likely impact on risk of a particular management option. This will need flow inputs from the whole of the Thames River Basin (although some catchments can be lumped and may not need to be assessed in great detail) and will need to transfer extreme waterlevels from the POL / Meteorological Office models into the study area (across the complicated system of banks in the outer estuary).

6.3.2 Intermediate Level An intermediate level modelling framework to provide the primary strategic modelling engine within which options can be tested and compared more reliably. This is likely to extend beyond the management / intervention boundary such that the full impact of any schemes can be adequately assessed, but is unlikely to extend beyond the normal tidal limit in either the Thames or tributaries.

6.3.3 Detailed Level A detailed level modelling framework will enable investigation of particular areas and the likely performance of impacts of specific options. This will probably take boundary conditions from the intermediate level models and the temporal and spatial extents will depend on the area and issues under investigation.

6.4 Recommendations i It is suggested that a hierarchy of spatial and temporal study boundaries should be adopted, enabling an appropriate understanding of physical processes and management intervention to be developed. ii The following initial study boundaries are proposed, however they should be continually reviewed in the light of new information and understanding.

Physical processes / understanding:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 72 S Large scale modelling to include the whole of the Thames River Basin extending east of the bank system in the outer estuary S Regional scale modelling to extend from Teddington Weir to Sea Salter / Foulness point and include the whole of the 1:1000 year flood outline area

Management / intervention area:

S Teddington Weir to Allhallows / Leigh on Sea and including the whole of the 1:1000 year flood outline area

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 73 7. RECOMMENDATIONS

1. The advice of the Port of London Authority and operators will be of paramount importance to assess the potential future navigation needs, as for example, the present navigation requirements may change in the coming years.

2. For the purpose of the Thames Flood Risk Management studies it will also be of considerable importance to understand the potential total discharge into the different parts of the estuary from the various sources (particularly CSOs) and the impact this will have on upriver storage capacity when barriers are closed.

3. At present the flood defence system in some of the creeks and tributaries is based on a combination of flood defence wall and a barrier or control structure. The closure of the barrier or control structure is often directly linked to the closure of the Thames Barrier. This policy was determined using the catchment criteria available at the time of the Thames Barrier study. The catchment criteria used at that time should be reviewed to determine their relevance for present and future Flood Risk management.

4. Advantage should be taken of any opportunity to clarify the level of each tide recording location. This should be carried out as soon as possible and additional tide recording locations established within the tidal estuary. An assessment of the potential impact of Ocean and Earth Tides on tidal water levels should also be undertaken to determine the through-tide variation at individual locations and from location to location at a given time.

5. Correlation of the shape of a surge, its height and duration require investigation. Initially this work can be confined to the water levels recorded at Southend and Sheerness immediately preceding, during and following a surge event. These data sets will identify the true surge as at these sites the influence of fluvial flow can all but be ignored. – an element that has not always been acknowledged as an influential component when assessing upestuary “tidal” water levels. The weather systems driving the surge should also be included in the assessment.

6. A pattern has been suggested where, just after low water on rising spring tides, there appears to be a positive surge with no apparent driving mechanism. The difference between actual and recorded levels, which can be in excess of 1m, follows a pattern that suggests the predicted tide could be in error. Examination of this “phantom surge” is necessary to eliminate flood risk measures being unnecessarily activated.

7. It is reported that extensive dredging of the River Thames led to a significant increase in tidal range at London Bridge in the nineteenth century. The impact of other extensive dredging in the twentieth century should be examined.

8. The potential impact of more frequent Barrier closures, on river morphology, should be examined as morphological change will impact upon the ecology of the estuary and should be investigated.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 74 9. Detailed assessment of the morphological change for the whole of the tidal Thames between Teddington to a point seaward of Southend since 1970 should be carried out to establish the changes that are taking place, how they interact with changes to tidal water levels and to provide background and base data for the Thames Flood Risk Management studies. Older historical data (including 19th century data) should be included but not in such detail.

10. The importance of having a good and robust understanding of the potential impact of climate change on tidal water levels is essential, as tidal water level is the principle driver of not only flood risk but the future ecological function of the estuary. UKCIP 2002 provides appropriate precautionary advice, but this is not likely to be adequate for the complete range of tasks that will require examination as part of the Thames Flood Risk Management studies.

11. It is strongly recommended that clarification / confirmation of the accuracy of the precise Ordnance Datum for each of the tidal water levelling locations is addressed as soon as possible. This recommendation is made because the uncertainty relating tidal water levels could lead to inaccurate or misinterpreted analysis of past and present tidal information.

12. It is recommended that additional water level monitoring locations are installed, especially up estuary of the barrier, to provide better coverage of the tidal propagation within the estuary.

13. It is recommended that a programme of ADP current velocity, salinity and the suspended solids concentrations (using Acoustic backscatter) not dissimilar in extent to that carried out for the Thames Barrier and associated works study be undertaken to provide the new round of studies with data appropriate to the task. The programme should include current velocity measurements in the Outer Estuary and tidal water levels throughout the estuary. These data should be collected to a programme that will be based on spring and neap tide data for both high and average/low fluvial flows.

14. While it is possible to predict local wave climates, it is recommended that a suitable series of wave measurements be undertaken to directly measure the variation in wave climate along the Estuary. This programme of work should include the measurement of the offshore directional wave climate and, simultaneously, the directional wave climates at a number of locations in the lower and middle Estuary. Records of meteorological conditions should also be made at each of the sites.

15. It is suggested that the NFCDD data be collated and entered for the whole of the estuary as a priority and that as soon as this information is available initial appraisal residual life and priority maintenance actions be prepared. This may usefully include a review of previous studies and if possible the recovery of condition data for the defences within Anglian Region.

17. The existing standard of service provided by the defences needs to be assessed in the light of the best available information. This is likely to be most appropriate after the elevations of water level gauges have been checked and models of the estuary have been shown to be capable of representing water levels accurately.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 75 18. Information on past and programmed expenditure on the flood defences within the estuary should be obtained. Historical data may usefully be obtained from Annual Reports produced by Flood Defence committees and anticipated expenditure identified from Medium Term Plans and discussions with EA Area Flood Defence Managers.

19. Liaison with TEP, MSEP, Essex Estuaries Initiative and other interested organisations should be maintained to facilitate a continued understanding of their work and consultation on flood management within the Thames Estuary when appropriate.

20. The Thames Estuary Flood Risk Management team should undertake continued liaison with ongoing and any future flood defence or water management studies with a view to establishing appropriate and consistent boundaries.

21. Discussions should be held with organisations responsible for developing national, regional and local policy and a programme of consultation organised to ensure that interested individuals and organisations are kept informed of progress and can contribute to the flood risk management plan. Developments in research and technology should also be monitored.

22. The 43 flood cells should be reviewed and revised as improved topographic and flood level information becomes available.

23. It is recommended that the assets at risk of flooding should be reviewed and updated using an appropriate methodology as improved information and techniques become available.

24. Liaison with the Thames Gateway Strategic Executive should be maintained and discussions (also including other relevant organisations) held to develop an approach to flood management for the proposed developments.

25. Progress of the NFCDD should be kept under review and arrangements put in place for the collection or collation of additional information enabling characterisation of existing and future defence performance.

26. It is suggested that a hierarchy of spatial and temporal study boundaries should be adopted, enabling an appropriate understanding of physical processes and management intervention to be developed.

27. The initial study boundaries should be continually reviewed in the light of new information and understanding.

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PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 81 APPENDICES

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 82 Appendix A

Planning for Flood Risk Management in the Thames Estuary A historical development of the Thames catchments

A.1 Introduction The river catchments that drain into the tidal Thames are shown on Drawing 02. The main catchments are summarised below.

Thames Region S Thames upstream of Teddington (catchment area about 10,000 km2). There are a number of tributaries in this catchment of which the largest are the Mole, the Colne, the Wey, the Blackwater, the Kennet, the Thame and the Cherwell. The catchment areas of these tributaries generally exceed 500 km2 and in some cases (the Wey and the Kennet) exceed 1,000 km2. S Tributaries and other local drainage areas that discharge directly into the tidal Thames including: - North Bank: The Crane, the Brent, the Lee and the Roding. Of these the Lee has by far the largest catchment area (over 1,200 km2). - South Bank: Beverley Brook, the Wandle and the Ravensbourne. These are all relatively small catchments. The total catchment area that discharges directly into the tidal Thames is about 3,000 km2.

Southern Region S Tributaries that discharge directly into the tidal Thames (South Bank) including the Darent and the Medway (total catchment area of the order of 2,000 km2).

Anglian Region S Tributaries that discharge directly into the tidal Thames (North Bank) including the Mardyke and the drainage channels in the vicinity of Canvey Island. The total catchment area is relatively small.

Thus the total catchment area that discharges into the tidal Thames is of the order of 15,000 km2, of which about 12,500 km2 discharges into the river upstream of the Thames Barrier.

A.1.2 Development The eastern part of the Thames catchment upstream of Teddington is highly developed but the western part less so. From Reading upstream the catchment is relatively undeveloped with a small number of large settlements including Swindon and Oxford. Much of the floodplain in this area is agricultural. However the area is developing rapidly, including extensive areas of new housing and light industry.

Downstream of Reading the amount of development increases, both on the floodplains and in the wider catchment. New development is proceeding rapidly. This is likely to lead to changes in runoff characteristics, and also an increase in flood risk caused by the presence of new developments on the floodplains.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 83 The catchment areas of some of the tributaries that drain directly into the tidal Thames are entirely within Greater London, and are therefore highly urbanised. The upper reaches of the Lee are relatively rural, although this river is extensively used for navigation and other purposes. Tributaries that drain into the Thames east of London are less developed but they drain some important industrial areas and also areas that are earmarked for major new developments. The major Thamesmead development east of Woolwich has been constructed on former Thames marshes and drainage water is discharged via pumping stations into the tidal Thames.

Over the years the development of the catchment has resulted in major changes to the river system in order to provide improved land drainage, flood defence, navigation and also to reduce the space occupied by the river corridor for development purposes. This has this changed the character of parts of the river systems. However, research has shown that it has not had a significant impact on runoff at the whole catchment scale (Crooks 1994).

A.1.3 The tidal limit –present and unprotected The developments referred to above have resulted in changes to the tidal limits of rivers draining into the tidal Thames. The tidal limit on the Thames is the control structure at Teddington weir, although there are tidal effects upstream on extreme high tides. For other rivers that drain directly into the tidal Thames, the following cases occur:

S The Thames tidal defences extend up the lower reaches of some tributaries to a control structure. This occurs, for example, on the Lee where the tidal limit is at Bow lock. S Some tributaries have an outfall structure at the confluence with the tidal Thames, and the tidal defences do not extend upstream. In such cases the tributary backs up when high fluvial flows combine with high tides, and this can lead to “freshwater” flooding of the lower reaches.

A.1.4 Run-off characteristics The primary impact of river catchments on flood risk in the tidal Thames is the amount of water that can enter the reach upstream of the Thames Barrier and the effect this has on flood levels and the operation of the Barrier.

By far the largest inflow into the tidal Thames is from the Thames upstream of Teddington. The flow record dates back to 1883 and the highest flow on the record was estimated to be 1,059 cumecs, in 1894. There has been a trend over the last 50 years of reduced frequency and magnitude of flood events on the non-tidal Thames (Crooks 1994). The last major event was in 1947, when the flow at Teddington was estimated to be 714 cumecs. Flood hydrographs on the Thames can last for several days (for examples, see Dunsmore 1997).

The inflow hydrographs for other tributaries on the tidal Thames are of shorter duration than the Thames and have a quicker response time. For a static storm over the catchment, flow from these tributaries would be discharged before the arrival of the flood from the main Thames catchment. However, a storm is not static, and comparison of hydrographs for historic events would be needed to determine the degree of co- incidence between hydrographs on the Thames at Teddington and hydrographs from the other tributaries.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 84 The primary cause of the largest floods on the Thames is large frontal weather systems that move from west to east. This can lead to flood flows from tributaries in the lower part of the catchment combining with the main flood from the upper catchment. Local scale flooding results from a variety of weather conditions, but the impact on the overall catchment is less significant.

A.1.5 Defence infrastructure Flood defence infrastructure in the River Thames catchment upstream of Teddington consists of the following:

S Control gates and control structures on the Thames and some tributaries, which can be opened to allow the passage of floodwater. S Enlargement of river channels by widening and dredging to improve flood capacity, and associated maintenance of these works. S “Engineered” river channels on some tributaries of the Thames which increase the flood capacity of watercourses, particularly those that pass through urban areas. S Construction of local flood alleviation measures and other engineering works, for example the Windsor, Eton and Maidenhead flood diversion channel on the Thames and the Lower Colne flood alleviation scheme which includes the Staines bypass channel and numerous other works.

Flood defence infrastructure on other rivers that drain directly into the tidal Thames includes the following:

S Enlarged and/or “engineered” river channels which increase the flood capacity of watercourses, particularly those which pass through urban areas. These include numerous culverts and other crossing structures. In some cases dredging and other maintenance work is needed to maintain the flood capacity. S Control gates at control structures, which can be opened to allow the passage of flood water. S Some tributaries have control gates at the confluence with the tidal Thames. These maintain the integrity of the tidal defences and prevent backflow of tidal water under the defences. In addition to the main tributaries, there are numerous smaller outfalls where backflow is prevented by flap gates. S Some of the tributaries with control gates at the confluence with the tidal Thames also have pumps to assist with the discharge of flood water during high tides, for example on the Wandle and drainage of the Thamesmead area. S Some tributaries have tidal defences in their lower reaches, either up to the control structure at the tidal limit (for example, on the Lee or the Crane), or up to a tidal flood defence barrier. S Other flood defence schemes, for example the Lower Lee flood diversion channel. S Tidal flood barriers on the Roding (Barking) and the Darent (Dartford). There are also three flood barriers in the vicinity of Canvey Island. There are concerns about the Barking barrier, because of the impacts of upstream development, and the Dartford barrier, because of instability of the river site.

Embankments and walls for fluvial flood defence are not generally used in the Thames Region. The impact of the above flood defence works would be to change the characteristics of flood flows downstream, as follows:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 85 S More “peaky” flood hydrographs with higher peak flows. S More rapid movement of the flood wave, changing the timing of the flood hydrograph on individual tributaries and consequently combined hydrographs downstream of confluences.

A.1.6 River use There are a wide variety of uses of the rivers that drain into the tidal Thames. The region is heavily developed, and watercourses form important landscape features in many areas. Specific uses include:

S Land drainage. S Water supply. S Discharge of waste water. S Navigation. S A wide range of amenity and recreational functions. Leisure activities include boating, fishing and walking (on the banks!).

Navigation is an important function of several rivers in the area, particularly the Thames and the Lee. Water levels in these rivers are controlled by a series of weirs with adjacent locks for vessels. Flood flows are to some extent controlled by the provision of gates in the control structures.

Rivers in the Thames catchment provide important potable water sources with a number of major abstraction points, particularly on the Thames west of London and on the Lower Lee which both supply London.

A.2 Contribution of catchments to flood risk

A.2.1 Flood risk on the tidal Thames Inflows from the catchments draining into the tidal Thames can contribute to flooding on the tidal Thames when high fluvial flows combine with high tides, particularly at the upstream end where the influence of the fluvial flow is greatest. For example, local flooding occurs at Richmond and local flood warning and flood defence measures have been provided.

By closing the Thames Barrier during the previous low tide, the impact of flooding caused in this way can be reduced. The Barrier closure provides a reservoir upstream to contain the fluvial inflow. It is therefore important to understand how fluvial flows will change in the future to assess the impact on flood risk from this source.

It was noted that during the winter of 2000/2001 there were periods when the tidal influence on water levels was very small in the upper part of the tidal Thames. This is a common effect associated with high fluvial flows in a tidal river, where low water levels are raised by the fluvial flow. However, the magnitude of the effect was surprising. It is possible that there are constrictions to fluvial discharge further downstream which contribute to this problem, and this should be investigated. In particular, it is suggested that work is undertaken to review the 2000/2001 fluvial flood flows and the corresponding operation of the Thames Barrier in order to better understand the linkage between the two and improve advice for operating the barrier during high fluvial flow conditions.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 86 Flood risk on tidally affected reaches of rivers that flow into the tidal Thames Where rivers flow into tidal estuaries, there is an interaction zone where maximum flood water levels depend on a combination of fluvial flows and tidal water levels. This is shown diagrammatically on Figure A1. The Thames at Teddington and other rivers that flow into the tidal Thames have control structures that affect the interaction zone and the extent of flood risk.

Fluvial zoneInteraction zone Tidal zone

Flood level HWL Water Level

LWL

Bed level

Distance

Figure A1 Tidal/fluvial interaction zone

Control structures can prevent tidal influence upstream if the highest downstream tide level does not affect levels upstream, as shown on Figure A2. In such cases the upstream flood level is affected by the backwater from the control structure, but is independent of the tide.

Fluvial zoneBackwater zone Tidal zone

Flood level Control structure HWL Water Level

LWL

Bed level

Distance

Figure A2 Impact of control structure on tidal/fluvial boundary: no upstream tidal influence

River catchments that drain into the tidal Thames contribute to flood risk on tidally affected reaches in the following ways:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 87 (a) Flood risk on tidal reaches of tributaries The lower reaches of some tributaries are tidal and effectively form an extension to the tidal Thames. The banks are protected by flood defences that have the same standard of defence as the adjacent tidal Thames.

For tributaries of this type which join the Thames upstream of the Thames Barrier, the causes of flood risk are the same as for the tidal Thames and the Thames Barrier can be operated to reduce flood risk. The tidal limit is normally at a control structure, which has the same standard of defence as the adjacent embankments. Downstream of the Thames Barrier, even if a facility existed, there is no need to lower water levels to accommodate fluvial flows because the inflows are relatively small.

(b) Flood risk on non-tidal reaches

(i) Tidal influence upstream of the “tidal limit” Flood risk on non-tidal reaches can be increased where the influence of the tide extends upstream of the structure at the normally accepted tidal limit, as shown on Figure A3. This occurs, for example, on the Thames at Teddington where the influence of extreme high tides extends upstream to . The extent of this tidal influence may change in the future because of sea level/land level changes and climate change.

Fluvial zoneInteraction zone Tidal zone

Flood level Control structure HWL Water Level

LWL

Bed level

Distance

Figure A3 Impact of control structure on tidal/fluvial boundary: tidal influence extends upstream

The magnitude of this effect is likely to be small under flood conditions, when water levels in the vicinity of the tidal limit are dominated by fluvial flows.

(ii) Backing up of tributaries during high tide periods For tributaries that have control structures at the confluence with the tidal Thames, there is a flood risk upstream of the tidal boundary. The tide causes fluvial flows to back up leading to an increase in upstream water levels, and this is shown on Figure A4. This effect occurs particularly on tributaries that have a sluice or flapped outfall into the tidal Thames that is closed during periods of

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 88 high tide. If high fluvial flows occur during these periods there is a serious risk of tide locked fluvial flooding.

Fluvial zoneBackwater zone Tidal zone

Control structure Flood level or tidal barrier HWL Water Level

LWL

Bed level

Distance

Figure A.4 Backing up of fluvial flow at tidal outfalls

This cause of flooding is of major concern to the Environment Agency. A particular concern is how to determine the magnitude of the flood risk, and how to designate the floodplains for planning purposes as required by PPG25. The magnitude of the flood risk is a joint probability problem involving both fluvial inflows and tidal water levels.

A further concern is the impact of gate failure or items jamming the gate open, thus allowing tidal inflow through the tidal Thames flood defences.

(iii) Tidal reaches upstream of tidal barriers The tidal barriers on tributaries downstream of the Thames Barrier are normally closed during high tide events, causing the river upstream to back up as shown on Figure A4. These barriers are normally closed when the Thames Barrier is closed. Whilst this appears to be a reasonable approach for tidal events, it is unlikely to be appropriate when the Thames Barrier is closed to reduce flood risk from high fluvial flows upstream of the Barrier.

There is a danger that these barriers could increase the upstream flood risk if they are incorrectly operated, particularly if the structure design allows the upstream level to exceed the downstream level.

In order to assess the impacts of fluvial flows into the tidal Thames, it is necessary to establish exactly what the existing flow regime is, and then investigate how it is likely to change in the future. This information can then be used as input to modelling of the tidal Thames to assess the overall impacts on flood risk caused by fluvial and tidal interaction.

A.2.2 Development and land use change Development could affect flood risk in the following ways:

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 89 S Increase in runoff, leading to higher peak flows downstream and therefore higher flood risk. S Change in the timing of runoff. This will affect the way in which hydrographs combine from different tributaries. This could lead to both increases and decreases in flood risk depending on local circumstances. S The assets at risk in flood risk areas will increase if further development is permitted. Flood risk is one of many considerations facing planners when making decisions on new development, and it is inevitable that development in floodplains will continue. However, where this occurs, greater care is being taken over design (for example, setting of floor levels) to minimise the impact of flooding.

The effect of new development on runoff will depend on the type of drainage provided. The use of Sustainable Urban Drainage Systems (SUDS) is intended to replicate natural drainage patterns and should not lead to increased runoff. However, these methods are not proven for large rainfall events and an allowance for increased runoff should be made in planning.

An associated concern is the impact of new flood alleviation measures on flood risk. New channel enlargements or flood relief channels will reduce hydrograph attenuation and increase downstream flows. Flood storage schemes generally reduce the flood risk immediately downstream, but their effect on flood risk in the catchment as a whole depends on their location.

There is much interest in the topic of land use change and impacts on flooding. Large scale changes such as changes in agricultural practices can have a significant effect on runoff, for example agricultural land drainage schemes. However the EUROTAS project has indicated that major land use changes have a relatively small impact at the scale of the Thames catchment, although the impacts are larger at smaller scales (Samuels 2001).

A.2.3 Climate change Climate change might be the greatest cause of future change in fluvial inflows to the tidal Thames. DEFRA are advising the use of a 20% increase in flood flows for sensitivity testing of climate change impacts. Whilst there is very little reliable information on the impacts of climate change on future fluvial flows, it clearly must be taken into account in any assessment of future flows and the resulting flood risk.

The 20% figure is understood to be based on the period 1961 to 1990, which was relatively dry. Flows were higher in the earlier part of the Twentieth Century, and there is little justification for increasing flow predictions based on the long-term Teddington/Kingston record by 20%.

A.2.4 Run-off characteristics Catchment runoff will change with time as a result of natural climate variability, climate change, catchment development and land use change. Studies will be needed to define fluvial inflows under present day conditions, and then to develop future scenarios for catchment runoff in order to assess future flood risk on both the tidal Thames and the tidally affected reaches of tributaries that flow into the tidal Thames. As mentioned in Section A.1.2, there has been little change in overall runoff in the Thames catchment over the last 100 years (Crooks 1994).

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 90 The impact of catchment areas adjacent to the tidal defences that drain directly into the tidal Thames must be included in the overall runoff assessment. Whilst the catchment area is relatively small compared to the overall Thames catchment, the percentage runoff and speed of response to rainfall will be relatively high.

It is essential that the runoff scenarios link with the proposed Catchment Flood Management Plans (CFMPs) for rivers in the Thames catchment. These studies will not only provide guidance on future inflows into the tidal Thames, but will also consider measures for reducing flood risk. Ideally the Flood Risk Management Strategy for the Thames estuary should be fully integrated with the CFMPs, particularly as they affect the most important flood risk area in the whole of the UK.

For this reason, CFMPs are dealt with in more detail in Section A.3.2.

A.2.5 Tidal inundation or tide locking The impacts of fluvial flows on flood risk and the resulting tidal inundation under present day conditions in the tidal Thames requires investigation. This will provide guidance on how the Thames Barrier should be operated to best manage the flood risk arising from combinations of fluvial flows and tidal water levels upstream of the Barrier.

It will then be necessary to investigate the likely future impacts on flooding caused by changes in the fluvial inflow in combination with the likely changes in the future tidal water level regime.

With regard to tide locking of tributaries on the tidal Thames, the extent of the existing problem needs to be understood. A strategy is also needed for development planning in the lower reaches of these rivers. At present the flood defence standard for tidal inundation from the tidal Thames is 1000-years, but the standard of defence for fluvial flooding caused by tide locking is lower than this. A consistent policy is needed for all tributaries on the tidal Thames.

Future flood risk caused by tide locking will depend on changes in fluvial inflows, changes in tidal water levels, and changes in land use in the flood risk areas. The impacts for each tributary will require investigation. It is likely that this work would form part of Flood Risk Management in the Thames Estuary as tidal water levels are a contributory factor to the flooding. However whatever measures are recommended, these must be reviewed in the relevant CFMP as part of the integration process between Flood Risk Management in the Thames Estuary and the CFMPs.

A.2.6 Defence infrastructure Fluvial inflows contribute to flood risk in the tidal Thames, tidally influenced reaches of some tributaries, and tidal reaches of other tributaries. There are opportunities to reduce the flood risk by modifying the existing flood defence infrastructure, which is outlined in Section A.1.5 above. This might be achieved by:

S Encourage the retention of floodwater in parts of the catchment to reduce flood flows. This might be done by flood storage in the upper parts of catchments. S Encourage the rapid discharge of floodwater from the lower parts of river systems. This would reduce flood flows by discharging runoff in advance of the main flood

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 91 peak. It might be achieved by adopting a policy of no stormwater attenuation for new developments and the provision of flood channels. S Policies for managing floodplains in high risk areas that include floodplain zoning, flood warning, provision of local defences and flood proofing of buildings. S Defending local areas of high flood risk.

Options for reducing peak flood flows include flood storage where suitable sites exist, and measures to change the timing of flood hydrographs from individual tributaries. Approaches of this type are relatively high risk because a lot of storage is needed to have a significant impact on a large catchment such as the Thames, and the performance of such measures will be dependent on present and future weather patterns. They may be more appropriate for the smaller catchments that drain directly into the tidal Thames.

However, there are large areas of floodplain that could be utilised for flood storage. There is also the option to introduce controlled washlands, where the operation of the storage areas is designed to achieve the optimum flood alleviation benefit.

There are severe constraints to the development of flood defence infrastructure because of the lack of suitable land. In particular, it could prove very difficult to obtain the necessary permissions to flood the large areas of land that would be needed for flood storage schemes, and land for engineering works in dense urban areas would be expensive and difficult to obtain.

A.2.7 Sediment load and distribution Sediment inflow from fluvial sources is not considered overall to be a major issue on the Thames when compared with the impacts of tidal sediments. However it would still be necessary to assess fluvial sediment issues especially in the upper reaches of the tideway to identify areas where sediment of a fluvial origin is a problem both now and potentially in the future.

A.2.8 Modification to fluvial flow In addition to the impacts of future climate and land use change on fluvial flows, there will also be changes caused by changes to drainage systems, water abstraction, etc. For example, urban drainage improvements might result in changes to storm and combined sewer outfall locations and flows. Whilst these impacts are likely to be relatively small compared with the overall inflows, they may have significant local impacts and should be investigated.

A.3 The physical environment

A.3.1 Fluvial flow In order to identify the fluvial hydraulic drivers of flood risk, the following types of studies will be required:

S Overview of fluvial flows into the tidal Thames under existing and future conditions, as part of the Inception Phase of Flood Risk Management Planning. S Fluvial inflows into the tidal Thames. This will provide boundary conditions for flood risk modelling of the tidal Thames. S Tidal influence on rivers that flow into the tidal Thames, including:  the Thames upstream of Teddington

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 92  other tributaries upstream of the normally accepted tidal limit  tidal reaches upstream of tidal flood barriers on tributaries S Thames Catchment overview, which will link with the proposed Catchment Flood Management Plans (CFMPs)

A summary of the data requirements for these studies is given below, including comment on current data availability.

Table A.1 Data set Data Data to Comment available be collected Catchment summary data  To include background land use maps, Indicative Floodplain Maps, etc. This is understood to be available from NCEDS, Twerton. Low term flow records at all  To include: relevant gauging stations on S all maxima the Thames and tributaries S hydrographs for selected historic events. Long-term rainfall data  Needed to extend flow records or create new flow records where there are no flow data at present.

Physical details for key Some Some Needed to review the accuracy gauging stations including of the high flow part of the potential by-pass routes rating curves.

Flow gaugings at existing  To be carried out on a “ad hoc” gauging stations basis to check high flow ratings.

Information on weather  patterns and historic storms.

Major future developments  Time horizon of available and other anticipated land use information will be short. changes in the catchment. Longer-term future scenarios will have to be estimated.

Catchment data for ungauged  Needed to assess inflows from tributaries and other catchment ungauged catchments. areas that discharge into the tidal Thames.

Reports and associated data  from studies which contain estimates of present and future inflows into the tidal Thames.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 93 Data set Data Data to Comment available be collected

Calibrated hydrodynamic  model of the Lower Thames

Data for tributaries and other Some Some These data should cover the catchment areas draining into catchments to just upstream of the tidal Thames: the limit of tidal influence. S Basic catchment information (area, land use, etc) S Main drainage network S Type of outfall into the tidal Thames, including details of structures, pumps, etc. S Relevant reports. S Summary of known flooding problems and causes. S Existing study reports S Any suitable existing hydraulic models.

Model input data for  These include topographical data catchments draining into the for channels, floodplains and tidal Thames where a model is structures. required but no suitable model exists at present.

Note: It is not proposed to carry out flow gauging at new sites as part of the study unless this need is identified during the Inception Phase. Generally the bulk of the catchment areas are gauged, and effort will be devoted to ensuring the flow records are as accurate as possible.

A.3.2 The existing flood defence system on river catchments

The existing flood defence system in the river catchments consists of a large number of interventions that provide a range of different standards of defence. The generic types of flood defences are as follows:

S Realignment, widening and deepening of natural channels. This is a common approach to flood defence in rural and low density urbanised areas. The standard of defence provided is generally relatively low. S Engineered channels to increase channel conveyance capacity in urban areas. These schemes can provide a high standard of defence but are often environmentally

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 94 unattractive. Adequate space for environmentally acceptable urban watercourses is a major constraint. These schemes include culverts, bridges and other structures. S Flood relief channels to improve channel conveyance capacity. These schemes can provide a high standard of defence. Schemes in the Thames catchment include the Lee flood diversion channel and the Windsor, Eton and Maidenhead Scheme, which has a 100-year defence standard. S Flow control structures. Several rivers in the catchment have been engineered to permit navigation, including the Thames and the Lee. Control structures adjacent to locks include gates that can be opened to permit the passage of floodwater without excessive raising of upstream levels. Providing the gates are large enough to pass flood flows, the river channel controls flood water levels. S Outfall structures where rivers discharge into the tidal Thames. These prevent backflow and therefore maintain the integrity of the tidal defences. However flooding can occur upstream as a result of backing up. S Walls and embankments. This type of flood defence, so common elsewhere in the UK, is not commonly used for flood defence in rivers upstream of the tidal Thames. There are lengths of embankments upstream of some control structures that contain moderate floods as part of the overall engineering works needed to control a river. S River maintenance is an essential component of flood defence in the Thames Region. Dredging and vegetation management is needed to maintain the capacity of watercourses, and rubbish clearance is vital in urban areas to prevent blockages.

There are many individual flood defence works on non-tidal rivers in the Thames Region. Many of these will have little impact on fluvial flows into the tidal Thames, or water levels in the tidally influenced reaches. It is recommended that lists of relevant works are prepared during the studies referred to in Section A.3.1 above. Works of particular importance will include:

S All outfall structures for watercourses which drain into the tidal Thames. S Control structures and other flood defence works on tidally influenced reaches of rivers. S Works on non-tidal reaches that significantly affect flows into the tidal Thames.

A.4 Study boundaries

Discussion of issues surrounding the selection of study boundaries and sub-division of the study area. Supported with GIS and other map based information for eventual inclusion in PAR and other reports. To include, where available, quantified areas, lengths, volumes, numbers to assist with future benefit / cost and other calculations. Where information is not available, data sets requiring collection / measurement will be identified.

The study boundaries for the catchment studies will be at two levels. The study boundaries for studies to predict fluvial inflows into the tidal Thames will be the catchment boundaries of catchments that drain into the tidal Thames. This includes the whole of the Thames Region together with relevant catchments in the Southern and Anglian Regions.

Flows will be predicted using a rainfall-runoff approach, calibrated against gauged flow data. This permits assessment of the impacts of future changes in rainfall and land use.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 95 The upstream boundaries for the more detailed studies of tidal influence on the tributaries will be just upstream of the estimated upstream limit of future tidal influence on each tributary (including the Thames upstream of Teddington). The study boundaries will also include the catchment areas that drain into the tributaries between the upstream boundary and the tidal Thames. Hydrological studies will be needed to predict the inflows both at the upstream boundary and from the catchment areas within the study boundaries.

A.5 Conclusions

The recommended studies for rivers that drain into the tidal Thames are as follows:

S Studies to predict fluvial flows into the tidal Thames under existing and future conditions. These will provide boundary conditions for flood risk modelling of the tidal Thames. S Studies to predict the tidal influence on rivers that flow into the tidal Thames under existing and future conditions, including:  the Thames upstream of Teddington  upstream of the normally accepted tidal limit on other tributaries  tidal reaches upstream of tidal flood barriers on tributaries S Thames Catchment overview, to provide an overall understanding of the catchment and facilitate co-ordination between the Thames Estuary studies and the proposed Catchment Flood Management Plans (CFMPs).

A large amount of existing data will have to be extracted from existing data sources and used in the studies. In addition, the following items of additional data collection will be needed:

S Physical details for some key gauging stations including potential by-pass routes. S Flow gaugings at existing gauging stations to check high flow ratings. S Catchment data for ungauged catchment areas that discharge into the tidal Thames. S Detailed data for the tidally influenced parts of catchments that drain into the tidal Thames that are including the main drainage network, details of outfalls into the tidal Thames, and a summary of known flooding problems and causes. S Model input data for catchments draining into the tidal Thames where a model is required but no suitable model exists at present.

APPENDICES S Database listing of reports, information etc. This should be done in co-operation with the Environment Agency.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 96 Appendix B

The Outer Thames Estuary

B.1. Introduction

Geographically the outer Thames Estuary can be considered to be the estuary eastward of a line between Shoeburyness and sheerness. However, there is not sufficient to describe the hydrodynamic transition from the lower Thames Estuary to the outer Thames Estuary. For the purposes of this study this will be considered to be a zone extending from about six kilometres to the west and ten kilometres to the east of the geographical boundary.

B.2 Context

The large quantities of sediment on the floor of the North Sea, originally laid down in the last glacial period which ended 10,000 years Before Present, are being reworked by present day tidal currents and wave action to produce the sediment patterns that we see today. The regional patterns broadly reflect the strength of the transport mechanisms: that is fine grade sands and muds are found in the deeper waters where tidal velocities are less strong, and fine muds and silts also accumulate at the margins of the estuary on flats, in creeks and estuaries. Medium grade sands and gravels are found in the mobile nearshore zones and medium sands are transported in the outer estuary in water depths of up to 20 m by the strong tidal currents (Whitehouse and Thorn, 1997). Sand is transported in the Southern Bight of the North Sea and moves past and into the outer estuary along a wide sediment transport pathway that lies west of 2ºE down the Suffolk coast and out to 3ºE, south of 52ºN. Within the estuary sand transport pathways exist around each of the major banks, circulating sand in a complex series of clockwise circulation cells (Figures 5.1 and 5.2).

It is the tidal streams in the outer estuary that have been mainly responsible for the development of the system of interdigitating banks and channels. Waves act as a stirring mechanism for sediment such that the transport rate due to tidal currents is increased in the shallower areas (Whitehouse et al, 1996). The banks and channels are present in those areas where there is a large thickness of unconsolidated sediments, and it is notable on the south side of the estuary that the presence at seabed of London Clay outcrops has restricted the formation of the banks and channels. The banks have remained relatively stable in a direction transverse to their long axis with the largest changes occurring in their length and the detailed pattern of depressions (swatchways) in their crestal regions, and the shallower areas where flood and ebb channels meet. The Edinburgh Channels are locations of rapid and sometimes unpredictable changes in the swatchway configuration. The five major sandbanks in the outer estuary – Kentish Knock, Long Sand, Sunk Sand, East and West Barrow and the Northeast Middle are sinks for fine to medium sand. Long Sand and Sunk Sand have extended appreciably towards the northeast during the last 150 years; in the case of the Sunk Sand by approximately 5 kilometres. Sunk Sand has also extended at its southern end, whilst in the last 10 years the form of the northern end of Long Sand has broadened appreciably. Anecdotal evidence for the movement of banks was also found in the HR Wallingford led SNS2 study where the computational flow model was compared with archive current meter data from the flanks of banks and at one of two points did not compare

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 97 favourably. On further inspection it was found that the bed levels at these points had changed by as much as 15 metres (since the 1970’s) (HR Wallingford, 2001).

B.3 Sediment Transport

Recently the schematic understanding of sediment transport in the outer Thames Estuary under every-day and storm wave and surge conditions has been presented in HR Wallingford (2002) and information below is drawn from this source. This built on and extended an earlier study (ABP Research & Consultancy, 1996). Seabed mobility in the outer Thames estuary has been determined from computational modelling and from observations of seabed features.

The most appropriate position for the offshore boundary is still a cause for much debate and at the greatest extent could be considered as a north-south line between Orford Ness in Suffolk and North Foreland in Kent. This line would then encompass the northeastern tips of the major sandbanks and also includes the complex coastline of Essex and south Suffolk. The north side of the outer estuary is flanked by wide intertidal areas with saltmarsh to landwards, and clay cliffs on the Tendring Peninsula, and on the south side by extensive mud flats with sand or shingle upper beaches backed by boulder clay or chalk cliffs.

Sediment exchanges of sand grade material across this boundary will occur on the seabed, and of gravel along the beaches. Fine sediment exchanges from the coastal area also lead to material being lost to the plume of fine material that extends out across the North Sea, especially in the winter months (Dyer and Moffat, 1998; Odd and Cooper, 1992).

The Kentish Knock, Sunk Sand and Long Sand are the main entry points for bedload from the Southern Bight (Figures 5.1 and 5.2). Clockwise circulation of sand around these banks brings sand into the inner reaches of the estuary where there are more mobile sandbank elements before being transferred northwestwards into the primary sink of the Maplin Sands and Dengie Flats. This accretion is confirmed by the 3% gain in volume that has occurred between 1991 and 1996, on the sand and mud flats between Dengie and Shoeburyness (Leggett et al, 1998).

The complexity of movement of sediments within the estuary is shown by the findings of Whitehouse et.al. (1996 – based on data from the mid-1970’s) who found that the net sediment flow in the centre of the main Warp channel was ebb dominated whilst on the banks at the channel sides the net flux is flood dominated. In addition Talbot et al. (1982) found that most of their Woodhead Drifters released in 7 different positions throughout the outer Thames Estuary, moved south and westwards into the estuary. They also found that of those released off the mouth of the River Crouch, many moved towards the Essex coast north of Bradwell. This suggested that the general southerly and westerly drift affecting most of the area was partly compensated by a northerly drift closer to the shore; a drift into the primary Maplin Sands and Dengie Flats sink.

There is a broad understanding of coastal transport around the margins of the estuary, but not much in the way of quantified rates. Coastal sediment transport on the north shore is localised and interrupted by the numerous creeks and estuaries. On the south shore the drift is predominantly westwards on the upper beach along the north Kent

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 98 coastline. Transport in the nearshore is westwards and of weak and variable magnitude, but may switch eastwards during storms. A narrow pathway from the south brings sand from the region of the Goodwin Sands into the Margate Sand and this pathway is reversed under some northerly wave dominated conditions. In addition there is an intermittent sediment pathway from the Margate Hook sandbank to the nearby shoreline, towards Minnis Bay (D’Olier, 1993).

B.4 Fisheries and bird feeding and breeding grounds

The Outer Estuary is important to a wide diversity of fish species. The estuary as a whole is important both for juvenile and post-juvenile stages of may species of fish. Twenty-two species of fish are commonly caught on a commercial basis. The estuary supports the largest cockle fishery within the UK. Changes to the sediment transport regime in the outer estuary and subsequently to estuary morphology may have an effect on these important resources.

The intertidal areas of the outer estuary (seawards of Gravesend) are important for their function as bird habitat. The estuary system is dynamic and in many areas the intertidals have been found to be accreting. However, the underlying situation is one of large exchanges of sediment over the intertidal areas and the trend for accretion can be reversed to one of erosion. This has been observed to occur between 1998 and 2002. The cause of erosion is unknown but probably attributable to changed meteorological conditions rather than changes to sediment sources within the estuary.

The influence of the present day flood risk management strategies on this area have not been determined in any detail, closure of the barrier is known to affect the estuary regime at least as far seaward as Sea Reach. The consequences of changes to operational strategies or new structures in this area will require significant investigation.

Detailed studies have been undertaken and are ongoing as part of the environmental impact assessment of the proposed London Gateway Port at Shellhaven. It will be necessary for studies associated with flood risk management, undertaken on behalf of the Environment Agency, to complement these existing investigations. The process underway for the proposed London Gateway Port will serve to inform and educate many of the various organisations who have an interest in the area and it will be this body of people who will be considering the future flood risk management plans of the Agency.

B.5 Flood defence and the environmental function of the Outer Estuary

The protection afforded to the Thames Estuary to the west of the Outer Estuary by the extensive area of intertidal banks also forms an essential part of the south-east Essex and north Kent flood defence works. Without this protection these areas would be subjected to the much more severe wave climate of the southern North Sea. This would potentially change the environmental function of the intertidal banks. An understanding of the impact of any Thames Flood Risk Management works on the flood defences or intertidal banks at the margins of the Outer Estuary is therefore essential.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 99 B.6 Data needs

The studies described, especially those recently completed, provide a reasonable understanding of the flow and sediment distribution in the Outer Estuary. The hydrodynamic and morphological processes are clearly dynamic and additional information will be required to improve the understanding of the processes especially in the transition zone between the Lower and Outer Estuary and in the western part of the Outer Estuary.

The following issues require further assessment, which in some cases will require the collection of additional data: -

S The seabed sediment distribution is known and the seabed sediment transport pathways have been mapped in HR Wallingford (2002), but it would be worth examining British Geological Survey seabed data for the seabed area south of the Deben and including the Thames Estuary. S Further investigation of the interaction process between waves-tides-currents and the significance for sediment transport. S Fine sediment processes can be further examined over a number of tidal cycles using an Acoustic Doppler Current Profiler to measure the structure of currents and use of calibrated acoustic backscatter readings to determine the suspended sediment concentration. This could be undertaken in conjunction with bed frame measurements to provide the longer term monitoring required to fully understand the annual situation, although the importance of spatial variability in sediment flux should be recognised. It is recommended to collaborate directly with PLA on measurements and to recognise the role of the Thames Estuary Partnership co- ordinated through the Environment Agency. S The assessment of available data and if necessary further monitoring and assessment of fisheries and bird feeding and breeding grounds.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 100 Figure B.1 North side of the Outer Thames Estuary (Suffolk and Essex) showing schematic sediment pathways for sand material – and licensed dredging areas – overlain

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 101 Figure B.2 South side of the Outer Thames Estuary (Kent) showing schematic sediment pathways for sand material – and licensed dredging areas - overlain

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 102 Appendix C

Combined Sewage Outfalls – Acton to Charlton

Distance from Teddington Location Weir (km) Acton Storm Water Outfall 14.5 LL1 (Main Line) near Chiswick Eyot 14.5 Stamford Brook, East Branch 15.3 West Putney Storm Relief 17.2 LL1 Storm Water Outlet at 15.6 NW Storm Relief 15.6 Hammersmith Pumping Station 15.7 LL No.1 Storm Outlet 18.3 Frogmore Storm Relief Sewer (into River Wandle) 19.6 Frogmore Storm Relief Sewer (into Bell Lane Creek) 19.6 Jews Row Pumping Station 20.1 Falcon Brook Relief 20.1 Falcon Brook Pumping Station Outlet 20.9 Lots Road Pumping Station 21.8 Church Street Sewer 22.4 Queen Street Sewer 23.0 Smith Street Main Line Outlet 23.5 Smith Street Relief 23.5 Ranelagh Main Line ( includes Sloane St and Ranelagh & 23.7 KSP SRS) Western Pumping Station (U/S of P Stn) 24.0 Western Pumping Station (Stn to River) 24.1 South West Storm Relief 24.9 Heathwall Pumping Station 24.9 KSP Main Line 25.3 Clapham Storm Relief 25.6 Brixton Storm Relief 25.7 Grosvenor Ditch 26.3 Horseferry Road 26.5 Wood Street 26.7 27.7 Northumberland Street 27.8 Savoy Street 28.0 Essex Street 28.7 29.1 Paul's Pier Wharf 29.5 London Bridge 30.4 Shad Thames Pumping Station Outlet 31.7 Battle Bridge - inlet controlled by penstocks 30.8 Beer Lane 30.9 Hermitage Dock 31.2

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 103 Distance from Teddington Location Weir (km) Wapping Dock 31.7 Cole Stairs Outlet 33.6 Bell Wharf Outlet 33.7 NE Storm Relief - Shadwell 33.7 Ratcliffe Cross 34.0 Earl Storm Relief 36.4 Wick Lane (into River Lea) 4.4km from R.Thames Holloway Storm Relief Sewer - London Wharf 34.1 Blackwall Sewer (Diversion) 34.9 Deptford Storm Overflow 37.4 Wick Lane (into River Lea) 4.4km from R.Thames Deptford Storm Discharge Culvert 38.2 Blackwall Basin 40.8 Isle of Dogs Pumping Station 40.5 Abbey Mills Pumping Station (into Abbey Creek then 4.4km from R.Thames River Lea) Abbey Mills Pumping Station (into Abbey Creek then 4.4km from R.Thames River Lea) River Lea, PS 2.3km from R.Thames Charlton Storm Relief 44.4

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 104 Appendix D

Bathymetric information held at HR Wallingford

Chart Title Surveys dated Area 201 The Warp and Oaze Deep 1978, 1985,1992 202 Barrow Deep West and Knob Channel 1973, 1976, 1980, 1988, 1994 203 Edinburgh Channels 1971, 1982, 1983,1984, 1985, 1991 204 Prince’s Channel 1971, 1972, 1974,1981,1990,1996 205 Queen’s Channel and Margate Sands 1971, 1977, 1991 207 Tongue Sand and NE Spit 1971, 1981, 1991 208 Black Deep 1971, 1984, 1997 209 Fisherman’s Gat 1980, 1991 210 West Swin 1992 211 West Swin, East Swin and Middle Deep 1976, 1983, 1993 212 Black Deep West 1985, 1992, 1999 214 Barrow Deep 1993 215 Barrow Deep – East 1986, 1993 216 King’s Channel – East 1975 301 Teddington Reach – part 1993 306 Brentford Reach – part 1982 308 Mortlake Reach 1983, 1995 309 Corney Reach – part 1995 310 Chiswick Reach – part 1995 311 Barn Elm Reach – Upper 1991 312 Barn Elms Reach – Lower 1991 313 Wandsworth Reach to Battersea Reach 1991 314 Battersea Reach to Chelsea Reach 1992 315 Nine Elms Reach 1984,1994 316 Lambeth Reach 1994 317 Kings Reach 1985, 1994 318 Upper Pool 1993 319 Upper Pool to Limehouse Reach 1987 320 Limehouse Reach to Greenwich Reach 1988, 1996 321 Greenwich reach to Blackwall Reach 1990 322 Blackwall Reach to Bugsbys Reach 1990, 1997 323 Woolwich Reach – Upper 1983, 1992 324 Woolwich Reach – Lower 1983, 1991 325 Gallions Reach 1983, 1991 326 Barking Reach 1984, 1991 327 Halfway Reach 1991 328 Halfway Reach to Erith Reach 1999 329 Erith Reach 1998 330 Erith Rands 2000 331 Long Reach – Upper 1988, 1994 332 Long Reach – Lower 1988, 1994 333 St Clements Reach 1974, 1978, 1983, 1990, 1995

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 105 Chart Title Surveys dated Area 334 Northfleet Hope 1974, 1978, 1981, 1985, 1986, 1993, 1999 335 Gravesend Reach – Upper 1977, 1981, 1987, 1993(May), 1993,(Sep), 1999 336 Gravesend Reach – Middle 1972, 1976, 1984, 1999 337 Gravesend Reach – Lower 1971, 1976, 1977, 1981, 1993, 1997 338 East Tilbury to Shornmead 1971, 1976, 1977, 1981, 1993, 1997 339 Shornmead to Lower Hope Point 1971, 1977, 1984, 1993 340 Sea Reach Mucking Flats to 1969, 1976, 1981, 1998 Thameshaven 341 Sea Reach Thameshaven to Canvey 1970, 1975, 1980, 1998 Island 342 Sea Reach Canvey Island to Southend on 1970, 1978, 1995 Sea 343 Sea Reach Southend on Sea to Sea Reach 1973, 1979, 1987, 1998 No 1 379 Barking Creek, River Roding 1971, 1979 382 Holehaven Creek, Upper Horse, Fobbing 1998 Creek 383 Holehaven Creek Entrance 1993 384 Easthaven Creek 1975, 1975(Aug) 385 Benfleet Creek 2000 386 Hadleigh Ray and Leigh Creek 1993 387 Vange Creek, Fobbing and Pitsea Creeks 1998 404 Lower Hope – South 1993, 1997 405 Lower Hope – Centre 1993 408 Shellhaven 2001 409 Coryton 2000 410 Holehaven 1993

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 106 Appendix E

Metadatabase listing

1 River Thames Tidal Flood Defence System: Reliability Study for the Environment Agency 2 London Tidal Defences: The Development of a Strategy for the 21st Century 3 Planning For The Rising Tides, The Humber Estuary Shoreline Management Plan 4 Lessons learned Autumn 2000 floods 5 Environment Agency Thames tidal defences: embayment studies. 6 Thames tidal defences: Embayment Studies Appraisal guidance note 7 Oil spill contingency landing - identification of sensitive habitats. Version 1, March 2000 8 Tidal Thames - Hydrodynamic Modelling Calculation of Defence Levels May 2002 9 Tidal Thames- Hydrodynamic Modelling Final Report May 2002 10 Hydrological data UK 11 Managemement Guidance for The Thames Estuary Principles of action. October 1999 12 North Kent Area Investment Framework Appendix F- Key Projects 13 Planning Policy Guidance Note 9: Conservation 14 Planning Policy Guidance Note 25: Development and flood risk 15 The Background To The Flood Defences of London and The Thames Estuary 16 Civil Engineering Heritage, London and the Thames Valley 17 Port of London Authority (PLA) tidal records, CORYTON TG 18 Port of London Authority (PLA) tidal records, MARGATE TG 19 Port of London Authority (PLA) tidal records, SOUTHEND TG 20 Port of London Authority (PLA) tidal records, TILBURY TG 21 Environment Agency (EA) tidal records, CHELSEA TG 22 Environment Agency (EA) tidal records, ERITH TG 23 Environment Agency (EA) tidal records, RICHMOND TG 24 Environment Agency (EA) tidal records, SHEERNESS TG 25 Environment Agency (EA) tidal records, SILVERTOWN TG 26 Environment Agency (EA) tidal records, SOUTHEND TG 27 Environment Agency (EA) tidal records, TILBURY TG 28 Environment Agency (EA) tidal records, TOWER PIER TG

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 107 29 Environment Agency (EA) tidal records, WESTMINSTER TG 30 Port of London Authority (PLA) tidal records, SOUTHEND TG 31 Port of London Authority (PLA) tidal records, SOUTHEND TG 32 Port of London Authority (PLA) Chart No: PLA 216 33 Port of London Authority (PLA) Chart No: PLA 335 34 Port of London Authority (PLA) Chart No: PLA 401 35 Port of London Authority (PLA) Chart No: PLA 301 36 Port of London Authority (PLA) Chart No: PLA 306 37 Port of London Authority (PLA) Chart No: PLA 308 38 Kent Area Local Environmental Agency Plan September 1999 39 Port of London Authority (PLA) Chart No: PLA 309 40 Port of London Authority (PLA) Chart No: PLA 310 41 Darent Local Environment Agency Plan September 1999 42 Medway Local Environmetn Agency Plan November 1999 43 Thames Habitat Action Plan 44 FCDPAG1 Flood and Coastal Defence Project Appraisal Guidance Overview (including general guidance) 45 FCDPAG2 Flood and Coastal Defence Project Appraisal Guidance Strategic Planning and Appraisal 46 FCDPAG3 Flood and Coastal Defence Project Appraisal Guidance Economic Appraisal 47 FCDPAG4 Flood and Coastal Defence Project Appraisal Guidance Approaches to Risk 48 FCDPAG5 Flood and Coastal Defence Project Appraisal Guidance Environmental Appraisal 49 Strategy for Flood and Coastal Defence in England and Wales. September 1993 50 The Humber Tidal Database and joint probability analysis of large waves and high water levels. Report No. R.810 51 Wandle, Beverley Brook and Hogsmill Local Environment Agency Plan July 2000

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 108 52 Thames Tideway (Teddington to Tower Bridge) Local Environment Agency Plan Consultation Report, July 1997 53 Thames Tideway (Teddington to Tower Bridge) Local Environment Agency Plan Action Plan, June 1999 54 Wandle, Beverley Brook & Hogsmill Local Environment Agency Plan Statement of Public Consultation, July 2000 55 Ravensbourne and Marsh Dykes Local Environment Agency Plan Consultation Report December 1997 56 Tidal Thames - Hydrodynamic Modelling of 31 October 2000 Event May 2002 57 Tidal thames- Hydrodynamic Modelling - Operational ISIS Model User Guide 58 Climate Change and the tidal Thames 59 An Action Plan for Flood Defence 60 Catchment Flood Management Plans Interim guidelines for consultation and pilot catchment studies. March 2001 61 Catchment Flood Management Planning Development of a modelling and Decision Support Framework (MDSF) MDSF Procedures Report EX4495 - Draft December 2001 62 Catchment Flood Management Planning Development of a modelling and Decision Support Framework (MDSF) MDSF Technical Annexes Report EX4497 - Draft December 2001 63 Modelling Estuary Morphology and Process Final Report, December 2000. Estuaries Research Programme, Phase 1 MAFF Contract CSA 4938 64 A Guide to Prediction of Morphological Change within Estuarine System. Version 1B Estuaries Research Programme, Phase 1. Report TR 114, December 2000. MAFF Contract CSA 4938 65 Thames Tidal Embayments Strategy Appraisal Methodology Review Report, Draft 3, July 2000

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 109 66 Essex Sea Walls Management Strategy Geomorphology Report No. S015-94-D, October 1994 67 Land use and transport planning in Kent Thames-side. Looking to an Integrated Future. March 1999 68 Greater Thames Estuary Coastal Natural Area Profile 69 Management Guidance for the Thames Estuary: Strategy 70 North Kent Coast - Isle of Grain to Dover Harbour Sub-Cells 4a & 4b - Shoreline Management plan 71 Essex Shoreline Management Plan 72 London Tidal Defence Strategy Plan Issue 1: April 1997 73 Thames Tidal Walls (West) Strategy Study Scoping Report. Report EX 4256, January 2001. 74 Learning to live with rivers 75 Shoreline Management Plans A guide for coastal defence authorities June 2001 76 The Thames Barrier 77 The Draft London Plan 78 The Water Framework Directive June 2002 79 Going East Thames Gateway: the future of London and the South East. 80 Review of Thames Tidal Defence Condition Survey Project No 9121 601, Report No23 Volume 1, May 1994 81 Flood Defence Management Asset Data Collection North Kent Subarea Thames Tidal Report, Volume 1 October 1999 82 The Flood Risk to London A Preliminary Scoping Study 83 Essex Coast and Estuaries Coastal Habitat Management Plan (CHaMP), Draft Final Report 7th May 2002 84 Essex CHaMP Comments (March 2002) 85 Essex Coast and Estuaries Coastal Habitat Management Plan (CHaMP) Comments on Draft report dated 15th March 2002 86 North Kent Coast and Estuaries Coastal Habitat Management Plan (CHaMP) Draft Report 25 June 2002

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 110 87 The potential development of Princes Channel for east-west navigation in the Outer Thames Estuary EX 3974 88 The potential development of Princes Channel for east-west navigation in the Outer Thames Estuary Numerical modelling EX3975 89 Riverside Jetty Study at Belvedere, Halfway Reach, River Thames,London The impact of the construction of a new jetty on the flowand sediment regime of the River Thames EX 4048 90 Millenium Bridge, Kings Reach, River Thames, London Physical model studies to examine the impact of the bridge on the river hydraulicregime during and post construction EX 3967 91 Thames Estuary Wave Modelling and Seabed Mobility Assessment EX3789 92 Hungerford footbridge Millennium Project, London The impact of the bridge works on the hydraulic regime of the River Thames EX 3810 93 Millennium Bridge, Kings Reach, River Thames, London The impact ofthe bridge during and post construction on the local hydraulicregime EX 3781 94 Protective works in the River Thames adjacent to Hungerford BridgeImpact of sheet piling and dredged trench temporary works on theriver regime EX 3452 95 Third Dartford Crossing Report on continuous silt monitoring in the River Thames - July 1988 to June 1989. EX 2104 96 Third Dartford Crossing Report on Continuous Silt Monitoring in the River Thames - July 1991 to June 1992. EX 2673 97 Tidal Thames Encroachment Study Study Report EX 3532 98 Thames Estuary Diver Shoal Training Works Silt Monitoring. EX3502 99 Sediment Transport Measurements at Maplin Sands Outer Thames Estuary Data Report TR 14 100 Thames Tideway Water Quality Model Preliminary Calibration Based on1990 Summer Data. EX 2687 101 Thames Estuary Diver Shoal Training Works Reappraisal of 1985 model study recommendations. EX 2681 102 Water Injection Dredging at Tilbury Bellmouth A study of the probable effects on the silt regime of the Thames Estuary. EX 2648 103 Shipwash area, outer Thames estuary Effects of dredging on nearshore wave conditions. EX 2522 104 East London River Crossing, River Thames Alternative bridge design by stanhope properties plc. Appraisal of hydraulic effects of three alternative bridge pier protection design schemes for protecting the bridgeagainst ship collision ship. EX 2173 105 Teddington flow proposal the effect on turbidity and siltation in the tidal Thames. EX 1350 106 Silt regimes: a study of Long Reach in the Thames estuary. SR 128

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 111 107 Southend island marina. Report on hydraulic studies for Brent Walker Group PLC. EX 1487 108 Flood risk map for England and Wales Report No. 130 109 Pitsea Marsh Water Level Management Plan May 1999 110 Water Level Management Plan for Benfleet and Southend Marshes SSSI Hadleigh Marshes Final Plan, July 1998 111 Vange & Fobbing Marshes Water Level Management Plan May 1999 112 Strategy for the Medway and Swale Estuary June 2000. 113 Lsle of Sheppey Strategy Plan Strategy Report (Volume 1) Revision 3, Septiembre 1998 114 North Kent Scoping Study Final Report Revision A02 September 2001 115 Elaboration of the Environment Agency's Flood defence Supervisory Duty 116 Planning Policy Guidance Note 20: Coastal Planning. Septemer 1992 117 Regional Planning Guidance for the South East (RPG 9). March 2001 118 National Appraisal of Assets at Risk from Flooding and Coastal Erosion, including the potential impact of climate change. July 2001 119 Thames Tidal Walls Records investigation and site survey Draft Final Report, March 1995 120 Thames Tidal Walls (West) Strategy Study Wind and Wales October 2001 121 RPG9a Thames Gateway Planning Framework 122 RPG 9b/3b Strategic planning guidance for the River Thames 123 Port of London Authority (PLA) Chart No: PLA 311 124 Thames Flood Prevention Investigation Field Survey Data, Section 1

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 112 125 Thames Flood Prevention Investigation Field Survey Data, Section 2 126 Thames Flood Prevention Investigation Field Survey Data, Section 3 127 Thames Flood Prevention Investigation Field Survey Data, Section 4 128 Thames Flood Prevention Investigation Field Survey Data, Section 5 129 Thames Flood Prevention Investigation Field Survey Data, Section 6 130 Thames Flood Prevention Investigation Field Survey Data, Section 7 131 Thames Flood Prevention Investigation Field Survey Data, Section 8 132 Thames Flood Prevention Investigation Field Survey Data, Section 9 133 Thames Flood Prevention Investigation Field Survey Data, Section 10 134 Thames Flood Prevention Investigation Field Survey Data, Section 11 135 Thames Flood Prevention Investigation Field Survey Data, Section 12 136 Thames Flood Prevention Investigation Field Survey Data, Section 12a & 12b 137 Catchment Flood Management Plan Medway Scoping Report, July 2001 138 St George`s Pier - Nine Elms Reach, River Thames. EX4318, March 2001 139 Local environment agency plan. Thames (Eynsham to Benson) and Ock.Consultation Report September 1997 140 Outer Thames Regional Model EX 4159 141 Development of Fulham Stadium, Barnelms Reach, River Thames, London. EX 4153, March 2000 142 Extension to the Northfleet Hope Container Terminal at Tilbury,River Thames, London Optimisation of design and an assessment ofthe hydraulic impact on the river regime. EX 4134 143 South Thames Estuaries and Marshes SSSI Water Level Management Plan 1998 144 Local Winds and Tidal levels in the Thames Estuary. HR Wallingford Report INT 92, July 1971

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 113 145 The silt regime of the Thames Estuary, HR Wallingford Report IT 175 January 1978 146 Port of London Authority (PLA) Chart No: PLA 336 147 Port of London Authority (PLA) Chart No: PLA 337 148 Port of London Authority (PLA) Chart No: PLA 338 149 Port of London Authority (PLA) Chart No: PLA 339 150 Port of London Authority (PLA) Chart No: PLA 340 151 Port of London Authority (PLA) Chart No: PLA 341 152 Port of London Authority (PLA) Chart No: PLA 342 153 Port of London Authority (PLA) Chart No: PLA 343 154 Port of London Authority (PLA) Chart No: PLA 379 155 Port of London Authority (PLA) Chart No: PLA 382 156 Port of London Authority (PLA) Chart No: PLA 383 157 Port of London Authority (PLA) Chart No: PLA 384 158 Port of London Authority (PLA) Chart No: PLA 385 159 Port of London Authority (PLA) Chart No: PLA 386 160 Port of London Authority (PLA) Chart No: PLA 387 161 Port of London Authority (PLA) Chart No: PLA 404 162 Port of London Authority (PLA) Chart No: PLA 405 163 Port of London Authority (PLA) Chart No: PLA 408 164 Port of London Authority (PLA) Chart No: PLA 409 165 Port of London Authority (PLA) Chart No: PLA 410 166 Port of London Authority (PLA) Chart No: PLA 201 167 Port of London Authority (PLA) Chart No: PLA 318 168 Thames Flood Prevention, Analysis of suspended solids regime prior to barrier construction. HR Wallingford Report EX 934, June 1980 169 Thames Water abstraction, The implications for the Port of London Authority of the findings of the NERC report on Thames water abstraction. HR Wallingford Report EX 1261, November 1984 170 Thames Estuary Flood Prevention, Continuous silt monitoring during Thames Barrier Construction. HR Wallingford Report EX 1279, February 1986 171 Thames Estuary Flood Prevention, Interim report on Thames Barrier post construction silt monitoring. HR Wallingford Report EX 2335, April 1991 172 Thames Estuary Flood Prevention, Final Report on Thames Barrier Silt Monitoring. HR Wallingford Report EX 2989, April 1994 173 Southern North Sea Sediment Transport Study, Phase 2. Inception Report. Report EX 4341, HR Wallingford, March 2001. 174 Southern North Sea Sediment Transport Study, Phase 2. Sediment Transport Report. Report EX4526, HR Wallingford, August 2002.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 114 175 Sediment transport measurements at Foulness in the Outer Thames Estuary. Report TR33, HR Wallingford, August 1997. 176 Sediment transport measurements at Maplin Sands, Outer Thames Estuary. Report TR15, HR Wallingford, September 1996. 177 Southern North Sea Sediment Transport Study: Literature Review & Conceptual Sediment Transport Model. Report No R.546, May 1996. 178 Port of London Authority (PLA) Chart No: PLA 202 179 Port of London Authority (PLA) Chart No: PLA 203 180 Port of London Authority (PLA) Chart No: PLA 204 181 Port of London Authority (PLA) Chart No: PLA 205 182 Port of London Authority (PLA) Chart No: PLA 207 183 Port of London Authority (PLA) Chart No: PLA 208 184 Port of London Authority (PLA) Chart No: PLA 209 185 Port of London Authority (PLA) Chart No: PLA 210 186 Port of London Authority (PLA) Chart No: PLA 211 187 Port of London Authority (PLA) Chart No: PLA 212 188 Port of London Authority (PLA) Chart No: PLA 214 189 Port of London Authority (PLA) Chart No: PLA 215 190 Port of London Authority (PLA) Chart No: PLA 312 191 Port of London Authority (PLA) Chart No: PLA 313 192 Port of London Authority (PLA) Chart No: PLA 314 193 Port of London Authority (PLA) Chart No: PLA 315 194 Port of London Authority (PLA) Chart No: PLA 316 195 Port of London Authority (PLA) Chart No: PLA 317 196 Offshore Isle of Thanet - Sand Transport Study. Thanet D.C. Internal Report. 197 Fluxes of suspended matter in the East Anglian plume Southern North Sea. 198 Monitoring Changes in Regional Ground Level, Using High Precision GPS. Technical Report W210, 1999 199 Beach evolution on the Southern North Sea coast. 200 The Tidal Thames Fact File. 201 Calibration of a 20km gridded 3D model simulating representative winter and summer M2 tidal and residual currents. HR Wallingford Report SR287. 202 Thames Gateway Review. 203 Investigation of dispersal of sewage sludge in the Thames Estuary. Fisheries Research Technical Report No 63, Part 1, 1-26. 204 Changing flood peak levels on the River Thames 205 River Thames Flood Hydrology Design Curves 206 The European River Flood Occurrence and Total Risk Assessment System (EUROTAS) 207 Port of London Authority (PLA) Chart No: PLA 418 208 Port of London Authority (PLA) Chart No: PLA 318 209 Port of London Authority (PLA) Chart No: PLA 319 210 Port of London Authority (PLA) Chart No: PLA 320 211 Port of London Authority (PLA) Chart No: PLA 321

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARY TECHNICAL SCOPING REPORT 115 212 Port of London Authority (PLA) Chart No: PLA 322 213 Port of London Authority (PLA) Chart No: PLA 323 214 Port of London Authority (PLA) Chart No: PLA 324 215 Port of London Authority (PLA) Chart No: PLA 325 216 Port of London Authority (PLA) Chart No: PLA 326 217 Port of London Authority (PLA) Chart No: PLA 327 218 Port of London Authority (PLA) Chart No: PLA 328 219 Port of London Authority (PLA) Chart No: PLA 329 220 Port of London Authority (PLA) Chart No: PLA 330 221 Port of London Authority (PLA) Chart No: PLA 331 222 Port of London Authority (PLA) Chart No: PLA 332 223 Port of London Authority (PLA) Chart No: PLA 333 224 Port of London Authority (PLA) Chart No: PLA 334 225 Port of London Authority (PLA) Chart No: PLA 335

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