Planning for Flood Risk Management in theThames Estuary

Technical Scoping Report

March 2003

Planning for Flood Risk Managementin the Thames EstuaryTechnical Scoping Report

Environment AgencyRio HouseWaterside DriveAztec WestAlmondsburyBristol BS32 4UD

March 2003

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARYTECHNICAL SCOPING REPORT - ii -

Publishing organisation

Environment AgencyRio HouseWaterside DriveAztec WestAlmondsburyBristol BS32 4UD

Tel: 01454 624400 Fax: 01454 624409

Environment Agency March 2003

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

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

Contract StatementThis report presents the scoping exercise conducted by HR Wallingford for Planningfor Flood Risk Management in the Thames Estuary. The Environment Agency, whoserepresentative was Sarah Lavery, commissioned the study and the HR Wallingford JobNumber was DAS 0806. Mervyn Littlewood and Matt Crossman prepared the reportwith key contributions from Paul Sayers, David Ramsbottom, Dr Richard Whitehouse,Dr Peter Hawkes, Dr Mike Dearnaley, Roy Atkins and Silvia Segura. The HRWallingford 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. HRWallingford accepts no liability for loss or damage suffered by the client or third parties as a result of errors or inaccuracies insuch third party data.

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARYTECHNICAL SCOPING REPORT - iii -

EXECUTIVE SUMMARY

Large areas of the Thames Estuary are potentially at risk from tidal flooding and arecurrently protected to a high standard by the defences constructed in the late 1970s andearly 1980s, which included the Thames Barrier at Woolwich and raised defenceseastwards to Southend-on-Sea and the Isle of Grain.

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

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

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

The summary of hydraulic processes within the estuary identifies considerable gaps ininformation and understanding where further data will probably be required. Onesignificant concern relates to the reliability of water level records and predictions.There is also only limited information available on the performance and condition of theexisting defences and some uncertainty as to the accuracy of the indicative floodplainmapping published by the Environment Agency. This situation will be improved withthe development of the National Flood and Coast Defence Database and completion of anumber of studies in 2003. The initial assessment of assets at risk of flooding dividedthe indicative tidal floodplain between Teddington and Foulness Point / Whitstable into43 flood risk compartments covering a total 468 km2 with capital values totalling morethan 99,000 million.

Recommendations for the scope and timing of further studies are presented withinAdvisory Report No. 1 in support of project development which has been preparedconcurrently.

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

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARYTECHNICAL SCOPING REPORT - iv -

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARYTECHNICAL SCOPING REPORT - v -

CONTENTS

EXECUTIVE SUMMARY iii

1. Introduction 1

2. The Thames Estuary A Context 22.1 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 263.1 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 454.1 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 625.1 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 706.1 Temporal 70

PLANNING FOR FLOOD RISK MANAGEMENT IN THE THAMES ESTUARYTECHNICAL SCOPING REPORT - vi -

CONTENTS CONTINUED

6.2 Management / intervention 71

6.3 Physical Processes / Understanding 72

6.4 Recommendations 72

7. Recommendations 74

8. References 77

TablesTable 2.1 Ranked extreme high waters at London Bridge and Sheerness 6

Table 2.2 Classification of flood defences by immediate hinterland 23

Table 3.1 Environment Agency water level data 27

Table 3.2 Port of London 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 Kent Shoreline Management Policy 47

Table 4.2 South Essex 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

FiguresFigure 2.1 Annual maxima tide 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 suspendedsolids concentration and other associated parameters 37

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CONTENTS CONTINUED

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

DrawingsDrawing 01 Indicative flood risk areas in the Thames EstuaryDrawing 02 Thames River basinDrawing 03 GeologyDrawing 04 Tidal defence systemDrawing 05 Environment Agency boundariesDrawing 06 Local authority boundariesDrawing 07 PopulationDrawing 08 Hydraulic measures locationsDrawing 09 Discharges and outfallsDrawing 10 Wind and wave dataDrawing 11 PLA chart extentsDrawing 12 Environmental designationsDrawing 13 Environmental resourcesDrawing 14 ArchaeologyDrawing 15 Extents of policy and strategy studiesDrawing 16 TopographyDrawing 17 Flood cellsDrawing 18 Proposed development are