Thurrock Council - Level 1 Strategic Flood Risk Assessment ...

Thurrock Borough Council Strategic Flood Risk Assessment Level 1

Thurrock Borough Council Level 1 Strategic Flood Risk Assessment

Final Report

Project Number: 60492009

June 2018


60492009 Final Report – June 2018 ii

Quality information

Prepared by Checked by Approved by

Sarah Betts

Graduate consultant, Water

Hannah Booth

Graduate consultant, Water

Amy Ruocco

Senior Consultant, Water

Emily Craven

Associate Director, Water

Sarah Littlewood

Senior Consultant, Water

Sarah Kelly

Regional Director, Water

Revision History

Revision Revision date Details Authorized Name Position

1.0 July 2017 Draft for comment

SK Sarah Kelly Regional Director

1.1 February 2018 Final EC Emily Craven Associate Director

1.2 April 2018 Final SK Sarah Kelly Regional Director

1.3 June 2018 Final amendments

SK Sarah Kelly Regional Director

AECOM Infrastructure & Environment UK Limited

Midpoint

Alencon Link

Basingstoke

Hampshire RG21 7PP

UK

T: +44(0)1256 310200

aecom.com

Prepared in association with:

Thurrock Borough Council

© 2018 AECOM Infrastructure & Environment UK Limited. All Rights Reserved.

This document has been prepared by AECOM Infrastructure & Environment UK Limited (“AECOM”)

for sole use of our client (the “Client”) in accordance with generally accepted consultancy principles,

the budget for fees and the terms of reference agreed between AECOM and the Client. Any

information provided by third parties and referred to herein has not been checked or verified by

AECOM, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM.


60492009 Final Report – June 2018 iii

Table of Contents

Abbreviations..................................................................................................................................... v

Glossary of Terms .............................................................................................................................. vi

Executive Summary ........................................................................................................................... ix

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

1.1 Approach to Flood Risk Management............................................................................. 1

1.2 SFRA Aims and Objectives ............................................................................................ 2

1.3 Flood Risk Policy and Guidance ..................................................................................... 3

1.4 User Guide .................................................................................................................... 4

1.5 Living Document ............................................................................................................ 5

2. Methodology ............................................................................................................................ 7

2.1 Overview ....................................................................................................................... 7

2.2 Consultation................................................................................................................... 7

2.3 Data Collection .............................................................................................................. 8

3. Assessing Flood Risk in Thurrock .......................................................................................... 10

3.1 Study Area ................................................................................................................... 10

3.2 Topography ................................................................................................................... 11

3.3 River Network ............................................................................................................... 11

3.4 Fluvial Flood Risk ........................................................................................................ 13

3.5 Tidal Flood Risk ........................................................................................................... 15

3.6 Surface Water Flood Risk ............................................................................................ 17

3.7 Geology and Groundwater flood risk ............................................................................ 19

3.8 Sewer Flood Risk ......................................................................................................... 20

3.9 Risk of Flooding from Reservoirs.................................................................................. 21

3.10 Historic Flood Events ................................................................................................... 22

3.11 Flood Risk Management Infrastructure ......................................................................... 24

3.12 Flood Defence Policy ................................................................................................... 26

4. Impact of Climate Change...................................................................................................... 32

4.1 Peak River Flow ........................................................................................................... 32

4.2 Peak Rainfall Intensity.................................................................................................. 33

5. Avoiding Flood Risk – Risk Based Approach to Planning ........................................................ 35

5.1 Sequential Approach .................................................................................................... 35

5.2 Applying Sequential Test – Plan-Making ....................................................................... 35

5.3 Applying Sequential Test – Planning Applications ......................................................... 39

5.4 Exception Test ............................................................................................................. 41

6. Managing and Mitigating Flood Risk through Spatial Planning and Development

Management ......................................................................................................................... 42

6.1 Overview ..................................................................................................................... 42

6.2 Development Layout and Sequential Approach ............................................................ 42

6.3 Finished Floor Levels ................................................................................................... 42

6.4 Safe Access/ Egress .................................................................................................... 43

6.5 Safe Refuge................................................................................................................. 43

6.6 Surface Water Management ......................................................................................... 43

6.7 Recommendations for Policy and Practice ................................................................... 44

7. Guidance for Developers ....................................................................................................... 45

7.1 What is a Flood Risk Assessment? .............................................................................. 45

7.2 When is a Flood Risk Assessment required? ................................................................ 45

7.3 How detailed should a FRA be? ................................................................................... 45

7.4 What needs to be addressed in a Flood Risk Assessment? .......................................... 47

7.5 Pre-application Advice.................................................................................................. 47

8. Summary ............................................................................................................................... 48


60492009 Final Report – June 2018 iv

8.1 Overview ..................................................................................................................... 48

Figures

Figure 1-1 Taking flood risk into account in the preparation of a Local Plan ........................................ 3 Figure 3-1 Lower Thames Crossing Route ........................................................................................ 11 Figure 3-2 Tilbury Integrated Flood Strategy Modelled Area ............................................................. 19 Figure 3-3 Tilbury Integrated Flood Storage Area – Drainage Outfalls .............................................. 22 Figure 3-4 Fobbing Horse Tidal Barrier (source: South Essex CFMP) .............................................. 25 Figure 3-5 Tilbury Flood Storage Area (source: EA 2009) ................................................................. 25 Figure 5-1 Application of the Sequential Test for the Plan Making Process ....................................... 36

Tables

Table 1-1 Flood Risk Policy and Guidance Documents....................................................................... 4 Table 2-1 SFRA Stakeholder Organisations and Roles ....................................................................... 7 Table 2-2 Fluvial Flood Zones (extracted from the PPG, 2014) ........................................................... 9 Table 3-1 Hydraulic models for Main Rivers in Thurrock (as of April 2018) ........................................ 14 Table 3-2 Thurrock Flood Alleviation Schemes ................................................................................. 29 Table 4-1 Peak River Flow Allowances for Thames River Basin District ............................................ 32 Table 4-2 Peak rainfall intensity allowance in small and urban catchments ....................................... 33 Table 4-3 NPPF Flood Zone and Vulnerability .................................................................................. 34 Table 5-1 Flood Risk Management Hierarchy and the SFRA process ............................................... 35 Table 5-2 Flood Risk Vulnerability Classification (PPG, 2014) .......................................................... 37 Table 5-3 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (PPG, 2014) ................................ 38 Table 7-1 Levels of Site-Specific Flood Risk Assessment ................................................................. 46

Appendices

Appendix A Recommendations for Policy and Practice

Appendix B Mapping of Available Data

Map 001 River Network

Map 002 Topography

Map 003 Superficial Geology

Map 004 Bedrock Geology

Map 005 Historic Flood Map

Map 006 Records of Sewer Flooding

Map 007 Risk of Flooding from Rivers and the Sea

Map 008 Risk of Flooding from Surface Water

Map 009 Susceptibility to Groundwater Flooding

Map 010 Risk of Flooding from Reservoirs

Map 011 Infiltration SuDS Suitability

Map 012 Environment Agency Flood Warning Areas

Appendix C Breach Modelling Flood Depth Mapped Results

Appendix D Breach Modelling Flood Hazard Mapped Results

Appendix E Breach Modelling Time to Inundation Mapped Results

Appendix F Techniques for SuDS in Thurrock

Appendix G Guidance for Thames Area Climate Change Allowances

Appendix H Climate Change Analysis for the River Mardyke

Appendix I FRA Checklist

Appendix J Thurrock SFRA Hydraulic Breach Modelling Methodology

Appendix K Maintaining the SFRA


60492009 Final Report – June 2018 v

Abbreviations

ACRONYM DEFINITION

AoCD Area of Critical Drainage

AOD Above Ordnance Datum

AIMS Asset Information Management System

AW Anglian Water

BGS British Geological Survey

CFMP Catchment Flood Management Plan

CLG (Department for) Communities and Local Government

Defra Department for Environment, Flood and Rural Affairs

ECC Essex County Council

DCLG Department for Communities and Local Government

FRA Flood Risk Assessment

FSA Flood Storage Area

FWMA Flood and Water Management Act 2010

GIS Geographical Information System

LFRMS Local Flood Risk Management Strategy

LFRZ Local Flood Risk Zone

LiDAR Light Detection and Ranging

LLFA Lead Local Flood Authority

LPA Local Planning Authority

LRF Local Resilience Forum

PPG Planning Practice Guidance

NPPF National Planning Policy Framework

RoFfSW Risk of Flooding from Surface Water

SA Sustainability Appraisal

SFRA Strategic Flood Risk Assessment

SPD Supplementary Planning Document

SuDS Sustainable Drainage Systems

uFMfSW Updated Flood Map for Surface Water


60492009 Final Report – June 2018 vi

Glossary of Terms

GLOSSARY DEFINITION

1D Hydraulic Model Hydraulic model which computes flow in a single dimension, suitable for

representing systems with a defined flow direction such as river channels, pipes

and culverts

2D Hydraulic Model Hydraulic model which computes flow in multiple dimensions, suitable for

representing systems without a defined flow direction including topographic

surfaces such as floodplains

Asset Information

Management System

(AIMS)

Environment Agency database of assets associated with Main Rivers including

defences, structures and channel types. Information regarding location, standard of

service, dimensions and condition.

Aquifer A source of groundwater comprising water bearing rock, sand or gravel capable of

yielding significant quantities of water.

Attenuation In the context of this report - the storing of water to reduce peak discharge of water.

Catchment Flood

Management Plan

A high-level plan through which the Environment Agency works with their key

decision makers within a river catchment to identify and agree policies to secure the

long-term sustainable management of flood risk.

Climate Change Long term variations in global temperature and weather patterns caused by natural

and human actions. Climate change values are based upon information within the

NPPF and Planning Practice Guidance as well as UK Government published

guidance: https://www.gov.uk/guidance/flood-risk-assessments-climate-change-

allowances

Culvert A channel or pipe that carries water below the level of the ground.

Design flood A flood event of a given annual probability against which the suitability of a

proposed development is assessed and mitigation measures, if any, are designed.

The design event is generally taken as; fluvial flooding likely to occur with a 1%

annual probability (1 in 100 chance each year), or tidal flooding with a 0.5% annual

probability (1 in 200 chance each year). Both should include a suitable allowance

for climate change.

DG5 Register A water-company held register of properties which have experienced sewer flooding

due to hydraulic overload, or properties which are ‘at risk’ of sewer flooding more

frequently than once in 20 years.

Exception Test If following application of the Sequential Test it is not possible, (consistent with

wider sustainability objectives), for the development to be located in zones with a

lower probability of flooding, the Exception Test can be applied if appropriate. For

the Exception Test to be passed: it must be demonstrated that the development

provides wider sustainability benefits to the community that outweigh flood risk and

a site-specific flood risk assessment must demonstrate that the development will be

safe for its lifetime, without increasing flood risk elsewhere, and, where possible,

will reduce flood risk overall

Flood Defence Infrastructure used to protect an area against floods, such as floodwalls and

embankments; they are designed to a specific standard of protection (design

standard).

Flood Resilience Measures that minimise water ingress and promotes fast drying and easy cleaning,

to prevent any permanent damage.

https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances



60492009 Final Report – June 2018 vii

GLOSSARY DEFINITION

Flood Resistant Measures to prevent flood water entering a building or damaging its fabric. This

has the same meaning as flood proof.

Flood Risk The level of flood risk is the product of the frequency or likelihood of the flood

events and their consequences (such as loss, damage, harm, distress and

disruption).

Flood Zone Flood Zones show the probability of flooding, ignoring the presence of existing

defences

Fluvial Relating to the actions, processes and behaviour of a watercourse (river or stream).

Freeboard Height of flood defence crests level (or building level) above designed water

level/flood level.

Functional Floodplain Land where water has to flow or be stored in times of flood.

Groundwater Water that is in the ground, this is usually referring to water in the saturated zone

below the water table.

ISIS A 1D hydraulic modelling software package.

Lead Local Flood Authority

(LLFA)

As defined by the Flood and Water Management Act, in relation to an area in

England, this means the unitary authority or where there is no unitary authority, the

county council for the area, in this case Surrey County Council.

Light Detection and

Ranging (LiDAR)

Airborne ground survey mapping technique, which uses a laser to measure the

distance between the aircraft and the ground.

Local Planning Authority

(LPA)

Body that is responsible for controlling planning and development through the

planning system.

Main River Watercourse defined on a ‘Main River Map’ designated by Defra. The Environment

Agency has permissive powers to carry out flood defence works, maintenance and

operational activities for Main Rivers only.

Mitigation measure An element of development design which may be used to manage flood risk or

avoid an increase in flood risk elsewhere.

Ordinary Watercourse A watercourse that does not form part of a Main River. This includes “all rivers and

streams and all ditches, drains, cuts, culverts, dikes, sluices (other than public

sewers within the meaning of the Water Industry Act 1991) and passages, through

which water flows” according to the Land Drainage Act 1991.

Residual Flood Risk The remaining flood risk after risk reduction measures have been taken into

account.

Risk Risk is a factor of the probability or likelihood of an event occurring multiplied by

consequence: Risk = Probability x Consequence. It is also referred to in this report

in a more general sense.

Sequential Test Aims to steer vulnerable development to areas of lowest flood risk.

Sewer Flooding Flooding caused by a blockage or overflowing in a sewer or urban drainage system.

Surface Water Flooding caused when intense rainfall exceeds the capacity of the drainage

systems or when, during prolonged periods of wet weather, the soil is so saturated

such that it cannot accept any more water.


60492009 Final Report – June 2018 viii

GLOSSARY DEFINITION

Sustainable drainage

systems (SuDS)

Methods of management practices and control structures that are designed to drain

surface water in a more sustainable manner than some conventional techniques.

Topographic survey A survey of ground levels.

TUFLOW A modelling package for simulating depth averaged 2D free-surface flows and is in

widespread use in the UK and elsewhere for 2D inundation modelling.


60492009 Final Report – June 2018 ix

Executive Summary

The National Planning Policy Framework (NPPF) and accompanying Technical Guidance emphasise

the responsibilities for LPAs to ensure that flood risk is understood and managed effectively through all stages of the planning process.

This Level 1 Strategic Flood Risk Assessment (SFRA) aims to facilitate this process by identifying the

spatial variation in flood risk across the Thurrock administrative area allowing a Borough-wide comparison of future development sites with respect to flood risk considerations.

The SFRA provides an overview of the risk of flooding from all sources across the Thurrock

administrative area and should be used to assist in the development of policy formulation, strategic

planning, development management and flood risk management. This SFRA identifies the tidal and

fluvial floodplains associated with the River Thames, main rivers and some ordinary watercourses

across the study area, presented in Flood Zone Maps included in Appendix B. These should be used for planning purposes when determining the suitability of development.

In the future, climate change is anticipated to have an impact on all sources of flood risk. It is

important that planning decisions recognise the potential risk that increased runoff poses to property and plan development accordingly so that future sustainability can be assured.

Thurrock is located adjacent to the River Thames to the east of London. It has over 30km of river

frontage and covers an area of 163km2 with more than half of the administrative area being defined as

Green Belt. In addition to the tidal flood risk posed by the River Thames to the south, there is a fluvial

flood risk posed by the River Mardyke which flows through the north western half of the study area with the Stanford Brook flowing through Stanford le Hope and the Manorway Fleet to the east.

The River Thames Tidal Defences (TTD) provide protection up to the 1 in 1000 year (0.1% AEP)

event along the Thames frontage with the standard of defence reducing down to sections of 1 in 20 year (5% AEP) in the more rural, upper reaches of the Mardyke.

Given the level of protection provided by fluvial and tidal flood defences within the Borough, there are

limited areas identified as Flood Zone 3b ‘Functional Floodplain’; however, some Flood Zone 3b is

defined in Tilbury, the upper Mardyke and Stanford Brook catchments. The majority of rivers within

the Borough are main rivers and the requirement for future maintenance and improvement of these defences is managed by the Environment Agency in collaboration with local stakeholders.

The residual flood risk, should existing flood defences fail, has been identified through reference to

Tidal Breach Modelling completed as part of this study in collaboration with the Environment Agency

and Thurrock Council. This data is presented within Appendix C, D and E and should be used when applying the Sequential approach to development location within Flood Zones.

Potential risk of flooding from other sources exists throughout the Borough, including sewer surcharge

and surface water flooding as a result of heavy rainfall and limited capacity of drainage infrastructure.

While the Environment Agency has not identified any areas with ‘Critical Drainage Problems1’ there

are surface water ‘flood risk hotpots’ located across the study area as identified in the Environment

Agency Risk of Flooding from Surface Water dataset and 14 Areas of Critical Drainage (AoCD) identified within the Thurrock Local Flood Risk Management Strategy

2

1 As defined by NPPF Paragraph: 003 Reference ID: 7-003-20140306

2 Thurrock Local Flood Risk Management Strategy, Thurrock Council, December 2015.


60492009 Final Report – June 2018 1

1. Introduction

In its role as the Local Planning Authority (LPA), Thurrock Council is currently preparing documents

that will form part of the Local Plan and set the vision for future development across the Borough up to 2036-37.

Thurrock Council faces the challenge of meeting the need for new development within areas already

identified to be at risk of both river (fluvial) and tidal flooding associated with a number of different

watercourses including the Thames, Mardyke and Stanford Brook. Furthermore, there is the potential

risk arising from more localised flooding from surface water generated by heavy rainfall, elevated groundwater, existing drainage systems as well as artificial sources.

1.1 Approach to Flood Risk Management

The National Planning Policy Framework (NPPF)3 and associated Planning Practice Guidance (PPG)

for Flood Risk and Coastal Change4 emphasise the active role LPAs such as Thurrock Council should

take to ensure that flood risk is assessed, avoided, and managed effectively and sustainably

throughout all stages of the planning process. The overall approach for the consideration of flood risk set out in Section 1 of the NPPG can be summarised as follows:

This has implications for LPAs and developers as described below.

1.1.1 Assess flood risk

The NPPF outlines that Local Plans should be supported by a Strategic Flood Risk Assessment

(SFRA) and LPAs should use the findings to inform strategic land use planning. Figure 1-1,

reproduced from the NPPG, illustrates how flood risk should be taken into account in the preparation of the Local Plan by Thurrock Council.

For sites in areas at risk of flooding, or with an area of 1 hectare or greater, developers must

undertake a site-specific Flood Risk Assessment (FRA) to accompany planning applications (or prior approval for certain types of permitted development).

1.1.2 Avoid flood risk

Thurrock Council should apply the sequential approach to site selection so that development is, as

far as reasonably possible, located where the risk of flooding from all sources is lowest, taking account of climate change and the vulnerability of future users to flood risk.

In plan-making this involves applying the Sequential Test, and where necessary the Exception Test to Local Plans.

In decision-taking this involves applying the Sequential Test and if necessary the Exception Test for specific development proposals.

1.1.3 Manage and Mitigate Flood Risk

Where alternative sites in areas at lower risk of flooding are not available, it may be necessary to

locate development in areas at risk of flooding. In these cases, Thurrock Council and developers

3 Communities and Local Government. 2012. National Planning Policy Framework. Available at:

https://www.gov.uk/government/publications/national-planning-policy-framework--2 4 Communities and Local Government. 2014. Planning Practice Guidance: Flood Risk and Coastal Change. Available at:

http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change/

Assess Flood Risk

Avoid Flood Risk

Manage & Mitigate

Flood Risk

https://www.gov.uk/government/publications/national-planning-policy-framework--2




must ensure that development is appropriately flood resilient and resistant, safe for its users for the lifetime of the development, and will not increase flood risk overall.

Thurrock Council and developers should seek flood risk management opportunities (e.g. safeguarding

land), and to reduce the causes and impacts of flooding (e.g. through the use of sustainable drainage systems).

1.2 SFRA Aims and Objectives

The purpose of this SFRA is to collate and present the most up to date flood risk information for use

by Thurrock Council to inform the preparation of the Thurrock Local Plan and prudent decision-making by Development Management officers on a day-to-day basis.

In order to achieve this, the SFRA will:

1) Refine information on the areas that may flood taking into account all sources of flooding and the impacts of climate change in accordance with latest guidance;

2) Inform the Sustainability Appraisal process, so that flood risk is fully taken into account;

3) Inform the application of the Sequential and, if necessary, Exception Tests in the allocation of future development sites, as required by the NPPF and planning application process;

4) Identify the requirements for site-specific Flood Risk Assessments;

5) Inform the preparation of flood risk policy and guidance;

6) Determine the acceptability of flood risk in relation to emergency planning capability; and,

7) Consider opportunities to reduce flood risk to existing communities and developments through better management of surface water, provision for conveyance and storage for flood water.

A SFRA for Thurrock Council was published in September 2009; however, due to updates in available

data, this Level 1 has been created as an update to the original SFRA report. This document has

been carried out to support the completion of the Sequential Test by Thurrock Council and inform the

allocation of sites within the emerging Local Plan. Documents recording the application of the

Sequential Test will be published as a separate document on the Council’s website. Should the

Sequential Test indicate that land outside flood risk areas cannot appropriately accommodate all

necessary development; a further Level 2 SFRA will be undertaken to consider the detailed nature of flood risk within each zone and support the application of the Exception Test.



Figure 1-1 Taking flood risk into account in the preparation of a Local Plan (PPG for Flood Risk and

Coastal Change, p6)

1.3 Flood Risk Policy and Guidance

There is an established body of policy and guidance documents which are of particular importance

when considering development and flood risk. These are identified in Table 1-11 including web links where further detail can be found if required.

LPA undertakes a Level 1 SFRA

The LPA uses the SFRA to:

(i) Inform the scope of the SA for consultation; and,

(II)Identify where developmenr can be located in areas with a low probability of flooding.

The LPA assesses alternative development options using the SA, considering flood risk (from all sources) and other planning objectives.

Can sustainable development be achieved through new development located entirely within areas with a low probability of flooding?

Use the SFRA to apply the Sequential Test and identify appropriate allocation sites and development.

If the Exception Test needs to be applied, consider the need for a Level 2 SFRA.

Assess alternative development options using the SA, balancing flood risk against other development objectives.

Use the SA to inform the allocation of land in accordance with the Sequential Test. Incllude a policy on flood risk considerations and guidance for each site allocation. Where appropriate allocate land to be used for flood risk managament purposes.

In clude the results of the Sequential Test (and Exception Test where appropriate) in the SA report. Use flood risk indicators and Core Output Indicators to measures the

Plans success.



Table 1-1 Flood Risk Policy and Guidance Documents

National Policy Documents

National Planning Policy Framework (para.

99-104)

https://www.gov.uk/government/publications/national-planning-

policy-framework--2

Planning Policy Guidance – Flood Risk and

Coastal Change


Flood and Water Management Act (2010) http://www.legislation.gov.uk/ukpga/2010/29/pdfs/ukpga_20100029

_en.pdf

Flood Risk Regulations (2009) http://www.legislation.gov.uk/uksi/2009/3042/pdfs/uksi_20093042_en.pdf

Environment Agency Standing Advice https://www.gov.uk/guidance/flood-risk-assessment-standing-

advice#vulnerable-developments-standing-advice

Regional Policy Documents

South Essex Catchment Flood Management

Plan

https://www.gov.uk/government/uploads/system/uploads/attachme

nt_data/file/288893/South_Essex_Catchment_Flood_Management

_Plan.pdf

Thames River Basin Management Plan https://www.gov.uk/government/publications/thames-river-basin-

district-river-basin-management-plan

Thames Flood Risk Management Plan https://www.gov.uk/government/publications/thames-river-basin-

district-flood-risk-management-plan

Thames Area Climate Change Allowances Guidance for their use in Flood Risk Assessments (Appendix G)

TE2100 https://www.gov.uk/government/publications/thames-estuary-2100-

te2100

Local Documents and Strategies

Thurrock Local Flood Risk Management

Strategy

http://democracy.thurrock.gov.uk/documents/s6554/Appendix%201

%20-

%20Thurrock%20Local%20Flood%20Risk%20Management%20St

rategy.pdf

Thurrock Core Strategy Policy CSTP27

Management and Reduction of Flood Risk

https://www.thurrock.gov.uk/sites/default/files/assets/documents/co

re_strategy_adopted_2011_amended_2015.pdf


River Thames




Addressing Climate Change



Tilbury Integrated Flood Strategy

Due for publish 2017/2018

1.4 User Guide

It is anticipated that the SFRA will have a number of end users, with slightly different requirements.

This Section describes how the SFRA should be used and how to navigate the report and mapping deliverables.

1.4.1 Strategic Planning and Policy

The chief purpose of the SFRA for Thurrock, in accordance with the NPPF, is to provide a strategic

overview of flood risk within the Borough to enable effective risk-based strategic planning for the

future through the preparation of the Local Plan. As part of the SFRA, a number of policy

recommendations and development management measures have been prepared to inform the development of the Thurrock Local Plan and in day-to-day decision making (Appendix A).





http://www.legislation.gov.uk/ukpga/2010/29/pdfs/ukpga_20100029_en.pdf

http://www.legislation.gov.uk/ukpga/2010/29/pdfs/ukpga_20100029_en.pdf

http://www.legislation.gov.uk/uksi/2009/3042/pdfs/uksi_20093042_en.pdf

http://www.legislation.gov.uk/uksi/2009/3042/pdfs/uksi_20093042_en.pdf

https://www.thurrock.gov.uk/sites/default/files/assets/documents/core_strategy_adopted_2011_amended_2015.pdf








1.4.2 Applying the Sequential Test

The NPPF sets strict tests to protect people and property from flooding which all LPAs are expected to

follow. The aim of the Sequential Test under the NPPF is to steer new development to areas with the

lowest probability of flooding. Section 3 and the supporting mapping in Appendix B provides the data

required to undertake the Sequential Test and Section 5 provides specific guidance on applying both the Sequential and where appropriate, Exception Tests.

1.4.3 Emergency Planning

Thurrock Council is a Category 1 Responder under the Civil Contingencies Act 20045 and therefore

has a responsibility, along with other organisations, for developing emergency plans, contingency plans and business continuity plans to help reduce, control or ease the effects of an emergency.

The SFRA deliverables, particularly Section 3, Appendix A and mapping of flood risk included in

Appendix B can be used by the Thurrock Emergency Planning team as a useful resource providing up to date information about flood risk.

1.4.4 Preparing site-specific Flood Risk Assessments

For those preparing site-specific Flood Risk Assessments (FRAs) for individual development sites, the strategic review provided by the SFRA provides a useful starting point for data gathering.

Section 5 provides guidance on the application of the Sequential Test for sites that have not been tested by the LPA, as well as details on when the Exception Test is required and how to apply it.

Section 6 provides guidance on flood risk mitigation and management measures that should be

considered for individual developments and Section 7 (also Appendix I) provides guidance for

preparing site-specific FRAs including when FRAs are required and what they should address depending on the scale of development and level of flood risk.

1.4.5 Assessing Planning Applications

Planning and development officers who are reviewing FRAs as part of the planning application

process should consult the SFRA mapping (Appendix B) to provide the background for flood risk and

suitability for SuDS measures. Sections 5 to 7 and Table 7-1 build on the guidance presented in the

PPG and Environment Agency Standing Advice and Appendix I can be used by those assessing applications as a checklist for issues that need to be addressed as part of site-specific FRAs.

1.5 Living Document

This SFRA has been developed building upon existing knowledge and updated breach and

overtopping modelling completed as part of this study. The Environment Agency review and update

the Flood Map for Planning (Rivers and Sea)6 on a quarterly basis and a rolling programme of detailed

flood risk mapping is underway. There are also several other model updates that might impact the outputs of this study and therefore need consideration:

The Environment Agency is concurrently developing a wider breach modelling scheme

around the Essex and Suffolk coast. Knowledge from this study should be shared so the breach model updates for Thurrock can be used in conjunction with the wider coastal study.

Hydraulic modelling and resulting Flood Zone maps for the Stanford Brook have been

recently updated by the Environment Agency and included within this SFRA. The River

Mardyke is due to be updated by the Environment Agency later in 2018. This will improve the

current knowledge of fluvial flood risk within the Borough, and may marginally alter predicted fluvial flood extents within parts of the Borough in the future.

The Tilbury Integrated Flood Strategy report is undergoing ‘final’ review and is due for

publication in 2018. This should be used in conjunction with this SFRA to assess the flood risk

5 HMSO 2004 Civil Contingencies Act 2004.

6 Refer to Section 3 for further detail.

http://www.legislation.gov.uk/ukpga/2004/36/contents



in Tilbury and the associated areas. The model outputs of this study have been included in the mapping provided in Appendices C-E Figure 8.



2. Methodology

2.1 Overview

Under Section 10 of NPPF, the risk of flooding from all sources must be considered as part of a

SFRA, including flooding from the sea (tidal), rivers (fluvial), land (overland flow and surface water), groundwater, sewers and artificial sources.

The methodology for the appraisal of flood risk from these sources is outlined below. Section 2.2

describes the approach to consultation and identifies the stakeholder organisations that have been

involved; Section 2.3 provides a description of the datasets used to assess the risk of flooding from each source.

2.2 Consultation

2.2.1 Duty to Cooperate

Under the Localism Act 20117, there is now a legal duty on LPAs to co-operate with one another,

County Councils and other Prescribed Bodies to maximise the effectiveness within which certain activities are undertaken as far as they relate to a ‘strategic matter’.

In complying with the duty to cooperate, Government Guidance recommends that LPAs ‘scope’ the

strategic matters of Local Plan documents at the beginning of the preparation process taking account

of each matters ‘functional geography’ and identify those LPAs and Prescribed Bodies that need to be constructively and actively engaged.

The Council prepared a Draft Sustainability Appraisal Scoping Report (2016)8 as part of the

background work required in preparing the Thurrock Local Plan. Flood risk is identified as a strategic

matter and specific engagement activities are proposed with a number of adjoining LPAs and Prescribed Bodies both in relation to the preparation of the SFRA and the Local Plan.

Table 2-1 SFRA Stakeholder Organisations and Roles

Stakeholder Organisation

Role with respect to the Thurrock SFRA

Thurrock Council as LPA

As a LPA Thurrock Council has a responsibility to consider flood risk in their strategic land use planning and the development of their Local Plan. The NPPF requires LPAs to undertake a SFRA and to use their findings, and those of other studies, to inform strategic land use planning including the application of the Sequential Test which seeks to steer development towards areas of lowest flood risk prior to consideration of areas of greater flood risk. During the preparation of the SFRA, Thurrock Council has provided access to available datasets held by the Council.

In addition, the SFRA will be used by the Thurrock Council Emergency Planning team to ensure that the findings are incorporated into their understanding of flood risk and the preparation of their flood plan.

Thurrock Council as LLFA and Highways Authority

As the LLFA, under the Flood and Water Management Act (FWMA) Thurrock Council has a duty to take the lead in the coordination of local flood risk management, specifically defined as flooding from surface water, groundwater and ordinary watercourses and to this end has prepared the Thurrock Council Local Flood Risk Management Strategy (LFRMS)

9.

Thurrock Council as LLFA is responsible for regulation and enforcement on ordinary watercourses and is a statutory consultee for future sustainable drainage systems (SuDS) for major developments following changes to the Town and Country Planning (Development Management Procedures) (England) Order 2015.

Thurrock Council is the Highways Authority and therefore has responsibilities for the effectual drainage of surface water from adopted roads insofar as ensuring that drains, including kerbs, road gullies and ditches and the pipe network which connect to the sewers, are maintained.

7 HMSO, 2011, Localism Act 2011.http://www.legislation.gov.uk/ukpga/2011/20/contents/enacted

8 Thurrock Council, 2016, Sustainability Appraisal Scoping Report (DRAFT)

https://www.thurrock.gov.uk/sites/default/files/assets/documents/localplan_sa_201602_draft_report.pdf 9 Thurrock Council, 2015, Thurrock Local Flood Risk Management Strategy

http://democracy.thurrock.gov.uk/documents/s6554/Appendix%201%20-%20Thurrock%20Local%20Flood%20Risk%20Management%20Strategy.pdf

http://www.legislation.gov.uk/ukpga/2011/20/contents/enacted



Stakeholder Organisation

Role with respect to the Thurrock SFRA

Environment Agency

The Environment Agency is responsible for managing the risk of flooding from Main Rivers and the sea and has a responsibility to provide a strategic overview for all flooding sources and coastal erosion.

The Environment Agency has a role to provide technical advice to LPAs and developers on how best to avoid, manage and reduce the adverse impacts of flooding. Part of this role involves advising on the preparation of spatial plans, sustainability appraisals and evidence base documents, including SFRAs as well as providing advice on higher risk planning applications.

The Environment Agency undertakes systematic modelling and mapping of fluvial flood risk associated with all Main Rivers in the study area, as well as supporting Lead Local Flood Authorities (LLFA) with the management of surface water flooding by mapping surface water flood risk across England. The Environment Agency has supplied available datasets for use within the SFRA.

The Environment Agency has been involved in the commissioning of the SFRA and has performed a technical review role of the draft project deliverables including the technical breach modelling methodology and positioning of updated breach locations.

Anglian Water Anglian Water (AW) is responsible for surface water drainage from development in the Anglian Basin District via adopted sewers and for maintaining public sewers into which much of the highway drainage connects. In relation to the SFRA, the main role that AW will play is providing data regarding past sewer flooding.

British Geological Survey (BGS)

BGS hold a number of datasets that have informed the SFRA, including superficial and bedrock geology, groundwater flooding potential and suitability of infiltration SuDS.

2.3 Data Collection

The following information and datasets have been made available by the stakeholder organisations and used to inform the assessment of flood risk from each of the sources of flood risk.

2.3.1 British Geological Survey

Appendix B Figures 3 and 4 contain BGS data on bedrock geology and superficial deposits. The

underlying geology governs subsurface groundwater movement, therefore understanding the geology

helps determine levels of groundwater flood risk across the Borough. Furthermore, the suitability of SuDS influenced by the underlying geology, therefore this information is valuable for developers.

2.3.2 LiDAR Topographic Survey

Appendix B Figure 2 shows the topography of the Borough based on LiDAR data and provides a useful basis for understanding local flood risk in the area.

Light Detection and Ranging (LiDAR) is an airborne mapping technique, which uses a laser to

measure the distance between the aircraft and the ground. Up to 100,000 measurements per second

are made of the ground, allowing highly detailed terrain models to be generated at spatial resolutions

of between 25cm and 2 metres. The data covering Thurrock has a spatial resolution of 2m. The

Environment Agency's LiDAR data archive contains digital elevation data derived from surveys carried out since 1998.

2.3.3 Detailed River Network

The Environment Agency ‘Detailed River Network’ dataset has been used to identify watercourses in the study area and their designation (i.e. Main River or Ordinary Watercourse).

2.3.4 ‘Flood Map for Planning (Rivers and Sea)’

The risk of flooding is a function of the probability that a flood will occur and the consequence to the

community or receptor as a direct result of flooding. The NPPF seeks to assess the probability of

flooding from rivers by categorising areas within the fluvial floodplain into zones of low, medium and

high probability, as defined in and presented on the Flood Map for Planning (Rivers and Sea)



available on the Environment Agency website. These Flood Zones have been presented in Appendix B Figure 7.

Table 2-2 Fluvial Flood Zones (extracted from the PPG, 2014)

Flood Zone Flood Zone Definition for River Flooding Probability of Flooding

Flood Zone 1 Land having a less than 1 in 1,000 chance of river flooding each year (0.1% annual probability). Shown as clear on the Flood Map – all land outside Flood Zones 2 and 3.

Low

Flood Zone 2 Land having between a 1 in 100 and 1 in 1,000 chance of river

flooding each year (between 1% and 0.1% annual probability).

Medium

Flood Zone 3a Land having a 1 in 100 or greater chance of river flooding each year (greater than 1% annual probability).

High

Flood Zone 3b Land where water has to flow or be stored in times of flood.

In the Environment Agency Flood Map for Planning (Rivers and Sea)

Flood Zone 3b is not separately distinguished as it is defined by the

LPA, not the EA. A description of Flood Zone 3b is included in

section 3.4.2, presented on Figure 7, Appendix B.

Functional Floodplain

The ‘Flood Map for Planning (Rivers and Sea)10

is a map showing the likelihood (annual chance) of

flooding from rivers and the sea in England, ignoring the presence of defences. The ‘Flood Map for

Planning (Rivers and Sea)’ dataset is available on the Environment Agency website and is the main reference for planning purposes as it contains the Flood Zones which are referred to in the NPPF.

The ‘Flood Map for Planning (Rivers and Sea)’ was first developed in 2004 using national generalised

modelling (JFLOW) and is routinely updated and revised using results from the Environment

Agency’s ongoing programme of river catchment studies. The studies can include topographic

surveys and hydrological and/or hydraulic modelling as well as incorporating information from recorded flood events. This data is replicated within Figure 7, Appendix B of this report.

Note; the Flood Zones shown on the Environment Agency’s Flood Map for Planning (Rivers and Sea)

do not take account the possible impacts of climate change and consequent changes in the future

probability of flooding. For further information on how climate change has been mapped within this SFRA, please refer to Chapter 4.

A second map, the Flood Risk from Rivers or the Sea is provided by the Environment Agency to

identify the risk of flooding including the effect of any flood defences present in the area. The mapped

results are not shown as flood zones, but as areas of high (>3.3% AEP), medium (between 1% and

3.3% AEP), low (between 0.1% and 1% AEP) and very low (<0.1% AEP) flood risk. This data can be

sought by accessing the ‘.Gov’ Flood Map for Planning Service11

however, for planning purposes the

‘Flood Map for Planning (Rivers and Sea)’ and associated Flood Zones remains the primary source of SFRA information.

Areas benefiting from flood defences are defined as those areas which benefit from formal flood

defences specifically in the event of flooding from rivers with a 1% AEP (1 in 100) chance in any given

year, or flooding from the sea with a 0.5% AEP (1 in 200) chance in any given year. If the defences

were not there, these areas would be flooded. An area of land may benefit from the presence of a

flood defence even if the defence has overtopped, if the presence of the defence means that the flood

water does not extend as far as it would if the defence were not there. Areas benefitting from flood defences are illustrated on Map 7 Appendix B.

10

Environment Agency ‘Long Term Flood Risk’ http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?topic=floodmap#x=237038&y=161974&scale=1 11

https://flood-map-for-planning.service.gov.uk/summary/497694/145364

http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?topic=floodmap#x=237038&y=161974&scale=1

http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?topic=floodmap#x=237038&y=161974&scale=1

https://flood-map-for-planning.service.gov.uk/summary/497694/145364



2.3.5 Risk of Flooding from Surface Water

The Environment Agency ‘Risk of Flooding from Surface Water’ dataset has been used to identify

areas at risk of flooding from surface water12

. This information has been supported through reference to the Thurrock Local Flood Risk Management Strategy

15 and Tilbury Integrated Flood Strategy.

2.3.6 Historical Records

Historic flood data has been provided from Thurrock Council and the Environment Agency. Flood

records from the Council13

largely include incidents attributed to surface water flooding, reported from

local residents and recorded within the Thurrock Local Flood Risk Management Strategy. These stem from minor drain blockages through to the flooding of entire roads.

The Environment Agency Historic Flood Map shows the maximum extent of all individual recorded

flood outlines from river, the sea and groundwater springs and shows areas that have previously been

subject to flooding in England. Records began in 1946 when predecessor bodies to the Environment

Agency started collecting detailed information about flooding incidents, although there are limited details about flooding prior to this date.

3. Assessing Flood Risk in Thurrock

3.1 Study Area

The study area is defined by the administrative boundary of Thurrock Council and is 163km2 in size. It

is adjacent to Greater London in the West (London Borough of Havering) and the Essex County (Brentwood, Basildon and Castle Point) in the north and east.

The River Thames forms the southern Borough boundary and Vange Creek flows from north to south

along the extent of the eastern boundary before discharging into the River Thames. The River

Thames forms 30km of tidally influenced riverfront adjacent to Thurrock. There are two other

significant Main Rivers: Mardyke, which flows into the Thames at Purfleet; and Stanford Brook which discharges in the Thames south of Stanford-Le-Hope.

Thurrock’s population was 168,400 in 201614

. The 2011 census recorded 62,353 households15

.

Metropolitan Green Belt covers 60% of the Borough; however, there still remains~200 ha of land

available for industrial use16

. The Borough forms part of the Thames Gateway regeneration area,

which is a corridor of opportunity identified by the government as an area with the greatest

development and commercial potential in the country. As such, much of the population and

commercial use is centred along the riverfront, this includes the Lakeside Shopping Centre and many

industrial and logistic sites, the ports of London Gateway and Tilbury with associated distribution

warehousing, a cruise liner terminal (Tilbury) and Purfleet Deep Wharf. There are several large landfill

sites located along the eastern extent of the Thames frontage that are coming to the end of operation

and the land is being restored.

Thurrock has good transport links due to its proximity to the River Thames and Greater London. The

M25 crosses the River Thames by bridge and tunnel between Dartford and Thurrock. Thurrock has

good east-west road connections with the A13 and A127 and a railway direct to London Fenchurch

Street that provides access to Central London. The Port of London Gateway and Port of Tilbury,

nearby connections to HS1 via Ebbsfleet and Stratford International Stations, and the airports of London City and Southend highlight that Thurrock is well placed in terms of international connections.

There are significant targets for new homes and jobs in Thurrock. The Thurrock Core Strategy

(adopted 2011) sets out a target for the Borough of 23,250 homes between 2001 and 2026 and

26,000 additional jobs. The 2017 published addendum to the Strategic Housing Market Assessment

12

https://flood-warning-information.service.gov.uk/long-term-flood-risk/map 13

Thurrock Borough Council (2015) Thurrock Local Flood Risk Management Strategy Available at: https://www.thurrock.gov.uk/sites/default/files/assets/documents/flood-risk-management-201512-v01.pdf 14

https://www.nomisweb.co.uk/reports/lmp/la/1946157204/report.aspx 15

Thurrock Borough Council (2015) Thurrock Joint Strategic Needs Assessment: Demographics and Population Change, Available at: https://www.thurrock.gov.uk/sites/default/files/assets/documents/jsna-demographics-population-v02.pdf 16

Available at: https://web.archive.org/web/20120514073519/http://thurrock.gov.uk/planning/strategic/content.php?page=factsheet_01

https://flood-warning-information.service.gov.uk/long-term-flood-risk/map

https://www.nomisweb.co.uk/reports/lmp/la/1946157204/report.aspx

https://www.thurrock.gov.uk/sites/default/files/assets/documents/jsna-demographics-population-v02.pdf



identified a housing need between 2014 - 2037 of up to 32,000 new dwellings in order to sustain the planned population growth and to provide housing to meet forecast job growth.

In addition, the government is planning a new road tunnel under the Thames Estuary which will link

the M25 near North Ockenden in Essex to the A2 near Shorne in Kent. The Lower Thames Crossing

aims to reduce the burden on the Dartford Crossing to the west and may lead to further growth across the study area.

Figure 3-1 Lower Thames Crossing Route

Source: Highways England 18th December 2017, http://roads.highways.gov.uk/lower-thames-crossing-in-my-area/

3.2 Topography

The River Thames flows eastwards along the southern Borough boundary where the land is low lying

with levels fluctuating around 0mAbove Ordnance Datum (AOD). Lower topography is also located in

the eastern Borough boundary, associated with Vange Creek and the western Borough associated

with the Mardyke where ground levels vary between 0mAOD and 5mAOD. In the centre of the

Borough at South Ockendon, Chafford Hundred and Orsett, the ground rises quickly away from the coast reaching 39m AOD in places. The highest elevation is ~109 m AOD at Westley Heights.

3.3 River Network

All watercourses in England and Wales are classified as either ‘Main Rivers’ or ‘Ordinary

Watercourses’. The difference between the two classifications is based largely on the perceived

‘importance’ of the watercourse with particular reference to its potential to cause significant and

widespread flooding. However, the watercourses classed as ordinary watercourses can still cause significant localised flooding.

The Environment Agency ‘Detailed River Network’ dataset has been used to identify watercourses in

the study area and their designation (i.e. Main River or Ordinary Watercourse). The Environment

Agency have duties and powers in relation to Main Rivers and the LLFA (Thurrock Council) have

duties and powers in relation to ordinary watercourses including ditches, dykes, rivers, streams and drains (not public sewers).

Light Detection and Ranging (LiDAR) data – Map 2 Appendix B

http://roads.highways.gov.uk/lower-thames-crossing-in-my-area/



The principal main river-designated watercourses within the Borough include: The River Mardyke,

Stanford Brook and Vange Creek. Additionally, there is an extensive network of arterial drainage

channels designated as Main River that drains Tilbury, the low-lying agricultural areas and tidal marshes.

3.3.1 River Thames

The Thames drains the whole of Greater London before discharging into the North Sea via the

Thames Estuary. It is tidally influenced for approximately 90km of its length up to Teddington in

Middlesex. The southern boundary of the Thurrock study area is formed by the River Thames which

has been heavily modified over time to include the construction of raised defences along its Thurrock

frontage. The defences are predominantly defined as ‘hard defences’ and largely provide a high

standard of defence, offering protection up to and in excess of 0.1% AEP (1 in 1000 year) level. Tidal

barriers have been constructed at the mouth of Tilbury Docks to protect this area, much of which is below sea level.

Extreme weather events are generated in the Thames Estuary when intense low pressure systems

over the North Sea artificially increase sea level due to the pressure gradient. This combined with

wind and wave action is referred to as a storm surge. The height of the storm surge typically becomes

greater as it moves south and the North Sea becomes narrower and shallower causing a funnelling

effect. The River Thames poses the greatest risk of flooding to Thurrock when storm surges coupled with high spring tides produce high tidal water levels in the Thames Estuary.

3.3.2 River Mardyke

The River Mardyke flows from the north to the west of the Borough, before discharging into the River

Thames at Purfleet. The river rises in the Brentwood Hills, north of the Borough border in the

neighbouring Borough of Brentwood. It drains a semi-rural catchment of ~112km2

and has an

approximate length of 18km from its source to the tideway of the Thames. There are two significant

tributaries, one of which flows east from Upminster and the other west from Langdon Hills. The

northern catchment is predominantly agricultural with clay soils giving a flashy flow regime with low baseline flows.

The south of the Mardyke catchment is more urbanised with residential and industrial uses. The

closest settlements are South Ockendon, North Stifford and Chafford Hundred. Downstream of Orsett

Fen the higher topography restricts the floodplain resulting in a greater risk of flooding to residents in Purfleet.

Modification of the Mardyke was undertaken as part of the 1980s land drainage scheme by the Essex

Rivers Authority. This included channel improvements, wash land storage and improved sluice

capacity to enhance land drainage within the catchment. The Mardyke discharges into the Thames at

Purfleet via Mardyke Sluice which prevents the tidal Thames from flowing up the Mardyke. The

Mardyke Sluice consists of double mitre gates and a guillotine gate set within concrete and masonry

abutments. There is an oval bypass culvert through the right hand abutment with two lines of defence formed by flap valves; there is a penstock at the upstream end.

3.3.3 Stanford Brook

Stanford Brook has a small catchment which drains south through Stanford-le-Hope and Mucking

Marshes before discharging into the Thames Estuary via Mucking Sluice. Victoria Road Brook joins

Stanford Brook in Stanford-le-Hope. Due to the steep surrounding topography and urbanised areas

the rivers responds rapidly during a rain event putting the surrounding population at risk of fluvial and surface water flooding.

3.3.4 Vange Creek

The eastern border of the Borough includes the marshes of Fobbing and Vange which drain into the

Vange Creek and Holehaven Creek, which are both Sites of Scientific Interest (SSSI). These creeks

River Network – Map 1 Appendix B



then flow to join the Thames at the Sea Reach section. Prior to the 1953 flood event, the Vange Creek

was navigable by sea. The Fobbing Horse tidal flood barrier was built on Vange Creek in the early

1980s as part of the wider Thames Tidal Defence Scheme to continue the primary defence line across

the creek from Fobbing to Bowers Marsh by limiting the passage of flood water up the creek. Three

gates drop from the roof of the structure into the channel to prevent water ingress when in operation, but also to retain a navigation function further up the creek (see section 3.11.4).

3.3.5 Arterial Drainage Networks

A network of drainage channels drain large areas of West Thurrock, Tilbury as well as northern areas

in the Mardyke catchment. Urban areas on the edge of the Thames Estuary generally have a

combination of gravity outfalls and pumps and low-lying areas around Tilbury have numerous

pumping stations to drain the marshlands which are below sea-level in places. The grazing marshes

have a system of irrigation channels to provide storage when gravitational outfalls are tide locked; this control of water level has an important influence on their habitat and landscape value.

The arterial drainage network may experience flooding as a result of several mechanisms, including:

High rainfall events in the local catchment,

Blocked channels,

Rainfall exceeding pump capacity at channel outlets, or

Pump failure are the downstream end of drainage channels which can cause out of bank

flows or the backing up of water behind defences at channel outlets

The responsibility for the maintenance of these Ordinary Watercourses falls to riparian owners who

own the land on either bank. Thurrock Council is only responsible for Ordinary Watercourses where land on either bank is in Council ownership or where historical agreements have been made.

3.4 Fluvial Flood Risk

Flooding from rivers occurs when water levels rise higher than bank levels causing floodwater to spill across adjacent land (floodplain). The main reasons for water levels rising in rivers are:

Intense or prolonged rainfall causing runoff rates and flows to increase in rivers, exceeding the capacity of the channel. This can be exacerbated by wet conditions and where there are significant groundwater base flows;

Constrictions in the river channel causing flood water to back up; and,

Constrictions preventing discharge at the outlet of the river, e.g. locked flood gates, or tide locking.

3.4.1 Hydraulic Modelling Studies

Table 3-1 provides a summary of completed hydraulic modelling studies in Thurrock which have been

used to inform the Environment Agency’s Flood Map for Planning (Flood Zone 1, 2 and 3a). The type of model (1D or 2D) is also specified, along with the corresponding available outputs for each model.

The scope of these modelling studies typically covers flooding associated with Main Rivers and

therefore Ordinary Watercourses that form tributaries to the Main Rivers may not always be included

in the model. Modelling of Ordinary Watercourses available on the Flood Map for Planning (Rivers

and Sea) may be the result of the national generalised JFLOW modelling carried out by the

Environment Agency and may need to be refined when determining the probability of flooding for an

individual site and preparing a site-specific FRA. The Thurrock Surface Water Management Plan should be referenced when addressing flood risk from surface water.



Table 3-1 Hydraulic models for Main Rivers in Thurrock (as of April 2018)

Watercourse Catchment Description Modelling Study

River Thames The River Thames defines the southern border of Thurrock and is tidally influenced at this location. The Thames Tidal Defences (TTD) protect these areas and therefore the risk of flooding to Thurrock is only if the defences fail (breach) or are exceeded (overtop).The tidal flood defences along the River Thames are mainly raised reinforced concrete walls, steel walls or earth embankments. The Environment Agency stated that defence height along the River Thames varies between 6.9mAOD and 7.2mAOD.

AECOM, 2016/ Level 1 Strategic Flood Risk Assessment Breach Modelling Technical Report. Updated breach modelling to include current terrain data and recommended allowances for climate change on extreme water levels in the Tidal Thames. The study area extends from Dartford to Fobbing, including the entire coastline within Thurrock.

Environment Agency, 2012 TE2100 Plan informs the residual Flood Zones 2 and 3 of the River Thames, which is based on national generalized modelling.

River Mardyke The catchment of the River Mardyke is approximately 102km

2. The catchment is low-

lying with an average elevation of 24mAOD; much of the catchment is below 10mAOD and is drained by numerous field drains.

The majority of the catchment is rural predominantly arable. Most of the urbanised areas are close to the downstream limit.

The outlet into the Thames Estuary is controlled by a set of mitre gates.

Further detail with regard to the River Mardyke and the hydraulic model used to inform this SFRA can be found from the Environment Agency.

JBA Consulting, 2011 Mardyke Flood Risk Study

Stanford

Brook

The catchment of Stanford Brook is relatively

low-lying.

Land use varies significantly from highly

urbanised to very rural with arable farming

accounting for most of the area.

Most of the watercourse is in a relatively

natural state; however, there are some hard

engineered schemes along its course as the

watercourse flows through Stanford-le-Hope.

Jacobs, 2017 Stanford Model Report.

Tilbury Tilbury is located on natural tidal floodplain

which has been reclaimed by the Thames flood

defences, therefore the topography is very flat

with ground levels around 0 m AOD.

The Tilbury Integrated Flood Strategy is an

integrated catchment model of the drainage

system in Tilbury and how the different

components interact during a storm event. The

study includes modelling of the Tilbury Flood

Storage Areas which was informed by the

Environment Agency’s previous Tilbury Flood

Storage Reservoir Study ISIS-TUFLOW model

(2015).

JBA Consulting, 2015 Tilbury Integrated Flood

Strategy

Un-named

Ordinary

Watercourses

There are a number of smaller drains, ditches

and ordinary watercourses which are ‘un-

modelled’ and have no Flood Zones defined.

Where data is un-available for these locations,

reference should be made to the Thurrock

SWMP and Environment Agency Risk of

Flooding from Surface Water.

URS Consulting, 2013, Thurrock SWMP

included TUFLOW direct rainfall modelling

including a standard ‘loss’ to account for water

entering the underground piped drainage

network.



3.4.2 Functional Floodplain (Flood Zone 3b)

The Functional Floodplain is defined in the NPPF as ‘land where water has to flow or be stored in

times of flood’. The Functional Floodplain (also referred to as Flood Zone 3b), is not separately

distinguished from Flood Zone 3a on the Environment Agency Flood Map for Planning. Rather the

SFRA is the place where LPAs should identify areas of Functional Floodplain in discussion with the Environment Agency.

For the purposes of this SFRA, existing hydraulic modelling data has been interrogated to identify

areas with an annual probability of 1 in 20 (5%) or greater flood extents to be delineated as Flood Zone 3b. Results have found:

There is no Flood Zone 3b associated with the River Thames due to the presence of formal flood defences providing protection to 1 in 1000 year (0.1% AEP);

Flood Zone 3b can be found on the Mardyke and its tributaries to the north of South Ockenden where the catchment becomes increasingly rural and the standard of protection is lower. There are lower flood defences upstream of Fobbing Barrier which only sees water up to the closure level of the barrier. Once the barrier is closed then levels do not rise any further.

The Stanford Brook is largely constrained as it flows through Stanford-le-Hope, however, Flood Zone 3b can be found to the south of the A13 and south of the urban envelope towards Mucking Marshes. Due to the steeper topography to the north, the watercourse is more restricted and hence has smaller floodplains.

Downstream of Fobbing Horse Barrier Vange Creek is protected by the Thames Tidal Defence System (TTD). Due to the presence of these formal defences the Standard of Protect is 1 in 1000 year (0.1% AEP) and therefore there is no Flood Zone 3b at this location.

Upstream of Fobbing Horse Barrier on Vange Creek there are no flood defences therefore it is possible that the surrounding marshland would flood in the 5% (1 in 20 yr.) scenario. There has been no hydraulic modelling of Flood Zone 3b (1 in 20 (5%) at this location, primarily due to its rural location.

Tilbury Flood Storage Area

Tilbury FSA area extent has also been added to the Flood Zone Map (Appendix B Figure 7). The FSA was engineered to store water in times of a flood, therefore the entire FSA area is shown as Flood Zone 3b, as it is functional floodplain.

Thames River Basin District Flood Risk Management Plan

The Thames River Basin District Flood Risk Management Plan provides policies on fluvial flood risk that are relevant to the study area. Further information on flood defence policy is available in Section 3.12.

3.5 Tidal Flood Risk

The Borough of Thurrock is bounded to the south by the River Thames and to the east by Vange Creek. The primary flood mechanisms associated with these tidally influenced watercourses are:

Daily tidal fluctuation, occurring when the freshwater Thames is met by the incoming tide from the North Sea;

Surge tides, which occur due to climatic conditions creating bands of low pressure in the Atlantic and North Sea. This causes a surge of water to move across the Atlantic, travelling southwards into the North Sea and becoming compressed as it travels towards and through the narrow English Channel, between Great Britain and mainland Europe. This causes a rapid rise in sea levels, which can be exacerbated by strong northerly winds; and

Environment Agency Risk of Flooding from Rivers and Sea – Map 7 Appendix B



The greatest overall flood risk from the Thames Estuary occurs when tidal surges coincide with

particularly high tide levels and/or fluvial flooding in the upper reaches of the catchment. As the flood

risk associated with fluvial mechanisms is relatively minor, compared to the tidal influence, the risk

from the River Thames is defined as tidal and addressed as such within this SFRA. Fluvial influences on this tidal risk have, however, been considered within breach modelling analysis.

3.5.1 Thames Tidal Breach Modelling

The Thames Tidal Defence system and Thames River Walls provide the Borough with a significant Standard of Protection (SoP) against tidal flooding; up to the 1 in 1000 year event (0.1% AEP) (see section 3.12 for further detail on flood defence infrastructure).

Whilst these defences provide a significant SoP to the Borough, it is essential to appreciate that they

are engineered structures which can only protect to a certain point, may malfunction and have a finite

design life. There will always therefore be a residual risk of flooding if defences breach due to

operational or structural failure. The likelihood of such residual risk is very small; however, the scale of

consequences from rapid inundation and deep water in heavily urbanised areas mean that these

residual risks must be considered. Equally defences may be overtopped if flood events exceed the design level of the defence (this is considered to be an actual risk).

As described above, the ‘Flood Map for Planning (Rivers and the Sea)’ provides information on the

areas of Thurrock that would flood if there were no flood defences or buildings i.e. this depicts the

“natural” floodplain. As indicated by the mapped Flood Zones, the areas at greatest risk of tidal

flooding in Thurrock (assuming no defences are present) include the London Gateway Port, Tilbury

and Grays. All of these areas are located within Flood Zone 3. It is important to recognise that the

flood risk identified along the Thames Frontage is a residual risk should flood defences fail or a design exceedance if defences were overtopped.

In order to better understand the residual flood risk, AECOM have been commissioned to update the

Thames Tidal Breach Modelling previously prepared to support the Thurrock SFRA in 2009/201017

.

This modelling simulates tidal breaches along the River Thames at a series of pre-determined breach

locations (21 in total along the Thurrock frontage). A review of breach locations previously assessed

was carried out during a workshop with an Environment Agency representative from the Partnership &

Overview team, Thurrock Council Project Manager, two representatives from the Environment Agency

Asset Performance Team and a representative from CH2M TEAM2100. Breach locations were

selected based on three main considerations: vulnerability to a breach; proximity to potential new development allocations; and, low points behind the defences.

As built drawings of required sluices and outfall structures have been provided by the Environment

Agency, these have also been used to inform the selection of breach widths. It was assumed that the

breach is ‘open’ for the duration of three tidal cycles (36 hours); this is the same duration of the previous SFRA breach models.

For the 2116 scenarios, the recommended climate change factors (UKCP09 medium emissions

95%tile) has been applied to generate the extreme water levels with allowance for sea level rise for

the 2116 scenarios. The climate change uplift has been applied to both the 1 in 200 (0.5%AEP) and 1 in 1000 year (0.1%AEP) tidal events.

Mapping to show the maximum depth and extent of flood water should a breach occur are mapped for

the 0.5% AEP (1 in 200 year) and 0.1% AEP (1 in 1000 year) scenarios. The modelling methodology

is included in Appendix J and Mapping within Appendix C (depth), D (hazard) and E (time to inundation).

3.5.2 Risk of Flooding from Tilbury Docks

The Port of Tilbury is located in the south of Thurrock on a loop of the River Thames southwest of

Tilbury. This part of the Thames lower reaches is characterised by vast areas of marshland. The port

17

Thurrock Borough Council, 2016 Level 1 Strategic Flood Risk Assessment Breach Modelling

Breach Modelling Mapped Results - Appendix C (depth), D (hazard) and E (time to inundation).



has been gradually evolving since the 1900s and now handles a variety of bulk cargo, timber cars and container traffic and remains one of Britain’s three major container ports.

The water levels in the Docks are controlled by a series of lock gates and the water level is

independent of water levels within the Thames, i.e. the water level does not rise and fall with the tide level.

There is a residual risk of a breach or failure of the lock gates during a tidal surge which could result

in overtopping of the dock walls and flooding of the surrounding area. This risk has been assessed

through breach modelling completed as part of this updated Level 1 SFRA. There are three breach

locations in proximity of the docks, being Til001 located at a pumping station to the west of the docks, Til002 located at Botney Sluice at the entrance to the docks and Til003, the Tilbury Barrier.

3.6 Surface Water Flood Risk

3.6.1 Thurrock Borough Council as LLFA

Overland flow and surface water flooding typically arise following periods of intense rainfall, often of

short duration, that is unable to soak into the ground or enter drainage systems. It can run quickly off

land and result in localised flooding. This source of flooding can be compounded when combined with

impermeable sub-soils, significant areas of development with associated hard standing areas or areas of open grassland.

Reference to the Thurrock SWMP and LFRMS; liaison with Thurrock Council and a representative

from the Environment Agency's Thames Estuary Asset Management (TEAM) 2100 programme, has identified areas with surface water flood problems.

The Thurrock LFRMS has identified 14 ‘Areas of Critical Drainage’ (AoCD), which are defined as

being ‘A discrete geographic area where multiple and/or interlinked sources of flood risk (surface

water, groundwater, sewer, main rivers and/or tidal) cause flooding in one or more Local Flood Risk Zones (LFRZ) during severe weather thereby affecting people, property or local infrastructure.’

The 14 AoCDs are spread across the Borough but mainly within urban areas. The locations covered by AoCDs include:

Purfleet Grays

Aveley

West Purfleet

Little Thurrock Marshes West Thurrock

West Thurrock

Tilbury

Stanford-le-Hope

Lakeside

East Tilbury

Bulphan

South Ockendon

Orsett

Information generated in the LFRMS has been used to create an action plan to reduce the risk and/or effects of surface water flooding, assisting Thurrock Council in their role as LLFA.

The 14 AoCD have been mapped in the Surface Water Flood Map included in Appendix B, for further detail on each AoCD please refer to the Thurrock Council LFRMS

18.

3.6.2 Environment Agency RoFSW

It should be noted that the NPPF also refers to areas with ‘critical drainage problems’ as notified by

the Environment Agency. However, these are not the same as critical drainage areas referred to

18

Thurrock Council (2015) Thurrock Local Flood Risk Management Strategy

Risk of Flooding from Surface Water Map – Map 8 Appendix B

Breach Modelling Mapped Results - Appendix C (depth), D (hazard) and E (time to inundation).



within the LFRMS and at the time of writing, the Environment Agency has confirmed that there are no ‘areas with critical drainage problems for the purposes of the Development Management Procedure Order’ within Thurrock.

The Environment Agency has undertaken detailed modelling of surface water flood risk at a national

scale and produced mapping identifying those areas at risk of surface water flooding during three probability events:

3.33% annual probability (1 in 30 year),

1% annual probability (1 in 100 year),and

0.1% annual probability (1 in 1,000 year).

The latest version of the mapping is referred to as the ‘Risk of Flooding from Surface Water’ (RoFSW)

and the extents can be freely accessed as GIS layers through the Environment Agency Geostore or accessed on their website

19.

3.6.3 Tilbury Integrated Flood Strategy20

Tilbury is at risk of flooding from surface water through a number of routes including surface water

runoff collecting in the low lying marshland, pumped outfalls, gravity systems and their tidal interaction and the underground sewer network.

Thurrock Council has completed the Tilbury Integrated Flood Strategy (Jan 2017) which includes

hydraulic modelling designed to better understand the relationship between the different sources of

flooding and their response to different rainfall events. The aim of the study is to inform the

understanding of asset performance amongst project partners particularly where flooding is shown to be caused by their interaction of assets owned by multiple partners.

19

Environment Agency Flood Risk from Surface Water Map http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?&topic=ufmfsw#x=357683&y=355134&scale=2 20

JBA Consulting (2017) Tilbury Integrated Flood Strategy

Risk of Flooding from Surface Water Map - Map 8 Appendix B

http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?&topic=ufmfsw#x=357683&y=355134&scale=2

http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?&topic=ufmfsw#x=357683&y=355134&scale=2



Figure 3-2 Tilbury Integrated Flood Strategy Modelled Area

Source: Tilbury Integrated Flood Strategy, January 2017

The output from the study includes mapped deliverables as well as an Action Plan for project partners

to implement over time. The Action Plan outlines where action is required and who is responsible, tying into the Thurrock Local Flood Risk Management Strategy and Environment Agency guidance.

3.7 Geology and Groundwater flood risk

3.7.1 Groundwater Flooding

Groundwater flooding occurs when water levels in the ground rise above surface elevations.

Groundwater flooding may take weeks or months to dissipate, as groundwater flow is much slower than surface water flow therefore water levels take much longer to recede.

Groundwater flooding is usually associated with chalk and limestone catchments that allow

groundwater to rise to the surface through the permeable subsoil following long periods of wet

weather. Groundwater flooding can also occur in areas where Made Ground has been deposited above impermeable subsoils, typically during ground raising or levelling works.

Local geology adjacent to the Thames Estuary is Solid Chalk; to the north there is a band of geology comprising the Solid Thanet Group and Lambeth group, beyond this to the north of the A13 is the London Clay Formation.

The Chalk bedrock is the principle underlying aquifer in the area. Rainfall percolates into the aquifer and recharges it. The London Clay prevents infiltration of rainfall in the northern part of the study area and therefore encourages the flow of surface water. The River Mardyke responds rapidly to heavy rainfall, which is linked to the impermeable London Clay in the upper catchment.

The Drift geology consists of Alluvium in the south of the Borough adjacent to the Thames Estuary. Alluvium is also present within the floodplain of the River Mardyke in the northern part of the study area. Alluvium consists of clays, silts, sands and gravels of which the permeability can be highly variable depending on the exact composition of the material. Since this material has been deposited



in riverbeds, it tends to be relatively impermeable. In between these two areas of Alluvium, there runs a band of undifferentiated river terrace deposits.

Information regarding the Solid and Drift geology within the Borough has been obtained from BGS

datasets and mapped in Appendix B. Additionally, the Groundwater Vulnerability map has been

supplied by BGS which confirm the presence of groundwater flood risk. These maps provide an

overview of the geology in the Borough and therefore an indication of the probability of groundwater flood issues.

It is unlikely that groundwater flooding will pose a significant flood risk within northern Thurrock, due to

the presence of clay, which creates a highly impermeable layer and restricts the movement of water both from the surface to the ground as well as the ground to the surface.

The presence of Chalk geology in southern parts of Thurrock around Aveley and Purfleet, covered by

permeable alluvial deposits, sand and gravel, indicates that this area could be susceptible to

groundwater flooding. The problem is exacerbated by the low-lying nature of the land, which is between 0-5m AOD.

The South Essex CFMP draws attention to the impact commercial chalk quarrying may have on

groundwater levels within Thurrock. During extraction of the chalk, the quarried areas become de-

watered. Since manufacturing came to an end and with it the de-watering activities, groundwater

levels have risen by approximately 60mm a year. Continued increases in groundwater levels could

lead to local flooding or structural problems for development located in close proximity to former quarries where restored ground levels may be lower than natural ground levels.

Despite this, it is considered unlikely that groundwater flooding will pose a significant flood risk within

Thurrock on a strategic scale, as the presence of London Clay will generally prevent groundwater

rising to the surface. Nonetheless, groundwater investigations should be carried out as part of site-

specific FRAs. This is particularly important for potential development sites near former quarried areas

and developments in which basement areas are proposed; it must be demonstrated that the site does

not lie on a key groundwater flow route such that introducing a flow barrier within the system would increase the risk of groundwater flooding elsewhere.

3.8 Sewer Flood Risk

During heavy rainfall, flooding from the sewer system may occur if:

1) The rainfall event exceeds the capacity of the sewer system/drainage system:

Sewer systems are typically designed and constructed to accommodate rainfall events with an annual

probability of 3.3% (1 in 30 chance each year) or greater. Therefore, rainfall events with an annual

probability less than 3.3% would be expected to result in surcharging of some of the sewer system.

While AW, as the sewerage undertaker recognises the impact that more extreme rainfall events may

have, it is not cost beneficial to construct sewers that could accommodate every extreme rainfall event.

Furthermore, as urban areas expand to accommodate growth, the original sewer system is rarely

upgraded proportionately and so becomes overloaded. This problem is compounded by climate

change which is forecast to result in milder wetter winters and increased rainfall intensity in summer months.

2) The system becomes blocked by debris or sediment:

Over time there is potential that road gullies and drains become blocked from fallen leaves, build-up of sediment and debris (e.g. litter).

3) The system surcharges due to high water levels in receiving watercourses:

Within the study area there is potential for surface water outlets to become submerged due to high

river levels. When this happens, water is unable to discharge. Once storage capacity within the sewer

Geology and Groundwater Flood Risk Map 3, 4 & 9 Appendix B



system itself is exceeded, the water may overflow into streets and potentially into houses. Where the

local area is served by ‘combined’ sewers i.e. containing both foul and storm water, if rainfall entering

the sewer exceeds the capacity of the combined sewer and storm overflows are blocked by high

water levels in receiving watercourses, surcharging and surface flooding may again occur but in this instance floodwaters will contain untreated sewage.

Anglian Water (AW) has provided data from their DG5 database to inform this study. The data consists of two registers: the ‘overloaded register’ and the Flood Management System (FMS).

I. The overloaded register is a database of incidents where Anglian Water has investigated properties with potential sewer flooding.

II. The Flood Management System is a register of any properties that have flooded due to sewer

overload. It should be noted that these are flood incidents that have been reported to AW by

the home owners. There are obviously incidents that don’t get reported and therefore will not show on the register.

The DG5 dataset has identified that there has been four sewer flood investigations carried out by AW,

with two of these investigations designated as high sewer flood risk and noted on the FMS database.

These both occurred in January 2017, one on Runnymede Road in Stanford-le-Hope and the other on the High Street in Aveley.

3.9 Risk of Flooding from Reservoirs

The Environment Agency dataset ‘Risk of Flooding from Reservoirs’ identifies areas that could be

flooded if a large21

reservoir were to fail and release the water it holds. This mapping identifies that

areas around Tilbury could be at risk of reservoir flooding if the Tilbury Flood Storage Area were to

fail. The mapping also shows areas along the River Mardyke at risk from reservoir flooding associated with The Sticking Hill Reservoir.

The failure of raised reservoirs could result in rapid inundation of the surrounding area with little to no

warning. The NPPG encourages LPAs to identify any impounded reservoirs and evaluate how they

might modify the existing flood risk in the event of a flood in the catchment it is located within, and / or whether emergency draw-down of the reservoir will add to the extent of flooding.

Reservoirs in the UK have an extremely good safety record. The Environment Agency is the

enforcement authority for the Reservoirs Act 1975 in England and Wales. All large reservoirs must be

inspected and supervised by reservoir panel engineers. It is assumed that these reservoirs are

regularly inspected and essential safety work is carried out. These reservoirs therefore present a minimal risk.

Thurrock Council is responsible for working with members of the Thames Valley Local Resilience

Forum (LRF)22

to develop emergency plans for reservoir flooding and ensuring communities are well prepared.

Any development plans within the risk of flooding from reservoirs will need to confirm with the Environment Agency the source of this reservoir flood risk.

3.9.1 Tilbury Flood Storage Area

The area north of Tilbury is classified as washlands and has been defined by the Environment Agency

as a Flood Storage Area. It is also registered under the Reservoirs Act (1975) and will be maintained

and operated as a category C Reservoir and Flood Storage Area (FSA) with capacity to store surface

21

A large reservoir is one that holds over 25,000 cubic metres of water, equivalent to approximately 10 Olympic sized swimming pools. 22

http://thamesvalleylrf.org.uk/

Sewer Flooding Incidents Map 6 Appendix B

Risk of Flooding from Reservoirs – Map 10 Appendix B



water floodwaters during a 0.1% AEP (1 in 1000 year) event. In 2012 the Environment Agency ran a

scheme to ensure that the FSA was compliant with the Matters for Safety outlined by the Inspecting

Engineer under the Reservoirs Act 1975. This involved the raising of embankments along sections of

the eastern and western parts of the FSA to ensure that it can withstand a 0.1% AEP (1 in 1000 year) flood event.

For the purpose of planning, this area is designated as functional floodplain (Flood Zone 3b) and

therefore nearly all types of development are inappropriate at this location. It is essential that the

Environment Agency is consulted before development plans are planned for sites within this area.

Figure 3.3 below is an extract from the Tilbury Integrated Flood Strategy23

showing the surface water drainage outfalls from the Tilbury Flood Storage Area.

Figure 3-3 Tilbury Integrated Flood Storage Area – Drainage Outfalls

Source: Tilbury Integrated Flood Strategy, January 2017

3.10 Historic Flood Events

3.10.1 Environment Agency Historic Flood Map

The Environment Agency Historic Flood Map shows the combined extents of known flooding from

rivers, the sea and groundwater. The Environment Agency does not generally map or model this kind

of flooding. However, where flooding from groundwater has occurred historically, and where the

Environment Agency have information on the extent of this flooding, the Environment Agency include it in the Historic Flood Map it in order that the information may be more widely available.

Caution should be applied when using historical records. It should be noted that as with all historic

flooding records, this information is largely anecdotal and does not always include a record of the

23

Tilbury Integrated Flood Strategy, JBA for Thurrock Council, January 2017



antecedent conditions giving rise to the flooding (therefore typically not attributed to a flood source) or reference to a flood return period.

3.10.2 Thurrock Council Recorded Flood Incidents

Thurrock Council has provided a database of incidents across the Borough from 2007-2014. From

this, the records involving flooding have been filtered and a GIS layer created. This has also been

added to the Historic Flood Map included in Appendix B. According to this data, there have been

upward of 450 flood incidents from multiple sources within this timeframe. The incidents recorded

range in magnitude of severity; some are small localised floods as a result of blocked/damaged gullies with others more widespread.

3.10.3 Tidal Flood Events

Historically South Essex and Thurrock has experienced tidal flooding on a large scale, due to its location on the Thames Estuary. The largest of these flood events were in 1897 and 1953.

Following the 1953 tidal surge, and subsequent local repairs and minor raising works, the 1972

Thames Barrier and Flood Protection Act was passed to construct the Thames Barrier - originally

designed to give a 0.1% AEP (1:1000 year) standard of protection to central London until 2030". Local

works were commissioned based upon the provisions of this Act, which resulted in the raising of tidal

defences within the Borough (and the rest of the Thames estuary) from Purfleet to Vange Creek. Tidal

barriers were also built at the entrance to Tilbury Docks and across Vange Creek. All major works were completed to give an effective defence line for the winter of 1982/83.

In addition, the Storm Tides Warning Services was established within the Met Office which provides a

forecast for the development and progression of Atlantic storms up to five days ahead and detailed, accurate information on the height of the surge and wave overtopping predictions two days ahead.

The risk of tidal flooding is therefore greatly reduced. Further detailed accounts of the tidal flood

events of 1897 and 1953 prior to the construction of existing flood defences can be found in the Thurrock Council Flood Warning Plan.

3.10.4 Fluvial Flood Events

There have been two significant fluvial flood events associated with Stanford Brook (September 1958)

and the River Mardyke (September 1968). During the 1958 Stanford Brook flood event 76mm of

rainfall fell in 2 hours resulting in 500 houses flooded above floorboard level in Stanford-le-Hope. The 1968 Mardyke affected the Fenchurch Street rail line and 2,400 acres of farmland flooded.

Since these events, conveyance/storage systems controlled by gravity outfalls subject to tide-locking

have been implemented and recent modelling studies have shown the benefit they have during a 1%

AEP (1 in 100 year) flood event for both the River Mardyke and Stanford Brook (Figure 7, Appendix

B). The presence of these defences decreases the likelihood of similar flood events occurring in the

future. However, the modelling shows the protection up to the 1 in 100 year only, therefore it is possible that flooding would occur in these areas during the 1 in 1000 year flood event.

3.10.5 Surface Water Flood Events

There have been numerous surface water flood events across the Borough, mainly in the urban parts

of Thurrock where impermeable surfaces dominate, including: Grays, Tilbury, Stanford-le-Hope and South Ockendon.

Thurrock Council has provided maps showing areas of previous surface water flooding. The incidents

have been digitalised and added to a GIS layer and displayed in the Flood Risk from Surface Water map (Map 8 Appendix B).

3.10.6 Sewer Flood Events

During the September 1968 event the East Dock Sewer in Tilbury caused significant flooding to the

area. In Tilbury alone the flooding affected 1km2

of the marshes and 1.25km2 of agricultural land.



1,750 houses were flooded and a further 950 affected by the event and Dock Road was closed for 4 days.

Historically, sewer flooding had been a particular problem in Stanford-le-Hope, Purfleet and Tilbury

due to inadequate maintenance of the sewer infrastructure which led to blockages or systems being

overwhelmed by the quantity of discharge24

. Anglian Water was involved in investigating schemes to

reduce the number and frequency of sewer floods and surface water drainage incidents. As shown by the DG5 register the number of sewer flood incidents have decreased.

3.11 Flood Risk Management Infrastructure

There are two main categories of flood defences, formal and informal (de facto). Formal defences are

specifically constructed to control floodwater. Informal defences include structures that have not

necessarily been constructed for this purpose but do have an impact on retaining flood water, such as railway and road embankments or other linear infrastructure such as boundary walls and buildings.

Information on flood defences has been provided by the Environment Agency from the Asset

Information Management System (AIMS). The AIMS provides details of the asset reference, location,

type of defence, level of protection provided by the structure and the geographical extent of the

defence or structure. Details of all AIMS flood defences in the study area are presented as a GIS layer.

Almost all the flood defences in Thurrock are maintained by the Environment Agency aside a few

privately owned defences, including: the raised defence at the pumping station at Aveley Marsh in

Purfleet, a culverted channel owned by Network Rail north of Tilbury and an earth embankment in Fobbing Marsh, which is not officially classified as a flood defence structure.

The majority of flood defences are Grade 2 or 3 (Grade 1 being the best classification and Grade 5 being the worst).

3.11.1 Thames Tidal Defences (River Walls)

The primary flood defences within the Borough are the River Thames defences, which in Thurrock are

mainly raised reinforced concrete walls, steel walls, or earth embankments which are recorded as

providing protection up to a 0.1% AEP (1 in 1000 year) tidal flood event. The Environment Agency

stated that the defence height along the Thames Estuary in Thurrock varies between 6.9m AOD and 7.2m AOD.

3.11.2 River Mardyke Defence System

Along the River Mardyke there are approximately 10km of maintained channels, including the

channels in close proximity to the Mardyke sluice and Stifford gauging station. These provide a

standard of protection in the upper catchment to South Ockenden to the 5% AEP (1 in 20 year) fluvial

flood event. In the lower catchment, between Purfleet and South Ockenden defences largely offer a

0.1% (1 in 1000 year) standard of protection. Defences along the fluvial channel are maintained by the Environment Agency.

3.11.3 Thurrock Sluices

There are multiple sluice gates in the Borough which act to prevent tidal waters propagating up

connecting rivers. This includes: Botney, Gobians, Mardyke, Mucking, St. Cleres, Stonehouse, West Thurrock and Worlds End Sluices.

24

Thurrock Borough Council (2009) Strategic Flood Risk Assessment

Risk of Flooding from Rivers and the Sea identifies flood defence lines and

areas benefitting from flood defences - Appendix B, Figure 7

Records of sewer flooding – Map 6 Appendix B



3.11.4 Flood Barriers

Flood Barriers are further important flood infrastructure reducing the flood risk in Thurrock. There is a

new flood gate at the entrance of Tilbury Docks. Fobbing Horse Flood Barrier controls water levels on

Vange Creek and protects the surrounding area from a 0.1% AEP (1 in 1000 year) tidal flood event. Upriver of the Fobbing Horse Barrier are embankments along Vange Creek.

Figure 3-4 Fobbing Horse Tidal Barrier (Source: South Essex CFMP)25

3.11.5 Tilbury Flood Storage Area

Tilbury Flood Storage Area, as described in Section 3.9.1, will store surface water during the 0.1% AEP (1 in 1000 year) event. The location of the flood storage area is identified in Figure 3.5 below.

Figure 3-5 Tilbury Flood Storage Area (source: Environment Agency 2009)

25

Environment Agency (2009) South Essex Catchment Flood Management Plan



3.12 Flood Defence Policy

3.12.1 Environment Agency TE2100

The Environment Agency has recently completed a comprehensive strategy referred to as Thames

Estuary 2100 (TE2100), to establish the best approach to manage flood risk in the estuary throughout the 21th century, taking into consideration various Climate Change scenarios.

Within the TE2100 Plan Thurrock is covered under four Action Zones and one Policy Unit within each

Zone as follows:

Action Zone 4 – East London downstream of Thames Barrier

Policy Unit - Rainham Marshes (Policy Approach P4)

The recommendation for this policy unit is to take further action to sustain the current level of

flood risk into the future (responding to the potential increases in risk from urban development, land use change and climate change).

Rainham Marshes & Mardyke policy unit forms the westernmost end of the Borough and is

part of the Thames Gateway regeneration area and is covered by Thames Strategy East in addition to the Thames Gateway Parklands vision.

This policy unit can provide important green space in the middle of an otherwise heavily

developed area. Redevelopment is planned for other parts of this policy unit, particularly the Channel Tunnel Rail Link.

Action Zone 5 – Middle Estuary

Policy Unit – Purfleet, Grays & Tilbury (Policy Approach P4)

The recommendation for this policy unit is to take further action to keep up with climate and

land use change so that flood risk does not increase.

Measures along Mardyke are not included as the flood risk from this source is classed as low.

Drainage system in Purfleet, West Thurrock and Tilbury areas will require upgrading as sea

level rises and storm rainfall increased. Mitigation measures could include improved outfalls

and drainage channels, additional pumping capacity, additional flood storage and new or improved local flood defences.

There is likely to be a limit to the number of times the new Tilbury Dock flood gate can be

closed because of interference with shipping, therefore raising the quay edges could be a mitigation option.

Action Zone 6 – Lower Estuary Marshes

Policy Unit – East Tilbury& Mucking Marshes (Policy Approach P3)

The recommendation for this policy unit is to continue with existing or alternative actions to

manage flood risk. Flood defences will be maintained at their current level, accepting that the likelihood and/or consequences of a flood will increase because of climate change.

It is likely that current defences will not be wholly replaced in future due to the low value of the

assets behind. However, local secondary defences for important assets and key infrastructure and residential areas, such as East Tilbury, may be more appropriate.

Managed realignment is planned at Mucking in association with the new London Gateway Port

to provide replacement intertidal area and saltmarsh.

Fluvial flood risk on the marshes is likely to increase as the sea level rises and fluvial flows

increase. Potential mitigation could include outfall improvements, flood storage and local flood defences.

Action Zone 7 – Lower Estuary,Urban/industrial Marshland

Policy Unit – Shell Haven & Fobbing Marshes (Policy Approach P3)



The recommendation for this policy unit is to continue with existing or alternative actions to

manage flood risk. Flood defences will be maintained at their current level accepting that the

likelihood and/or consequences of a flood will increase because of climate change. This policy will be supplemented with improved defences to protect key sites such as Coryton.

The Fobbing Horse Barrier may not be appropriate for future flood risk management. Removal

of the barrier would result in gradual overtopping of the existing tidal defences into the marsh

land, allowing the marshes at Fobbing and Vange to become more brackish, hence supporting

natural change. If removed, this will alter management arrangements for the secondary defences on Vange Creek.

The drainage systems on Fobbing and Vange Marshes will require upgrading as the sea level

rises and rainfall increases; this will mainly consist of improvements to channels and outfalls

as the need arises. There could be issues of saline intrusion and siltation at outfalls as there is

heavy siltation in Vange and Holehaven Creeks. Previously outfalls have been abandoned and reconstructed elsewhere as a result of this process.

3.12.2 Integrating TE2100 with Flood management in Thurrock

Thurrock Council is committed to working with the Environment Agency and others to ensure the

recommendations of the TE2100 Plan are implemented in new and existing developments, to keep

communities safe from flooding in a changing climate and improving the local environment. The

implications for local policy on development in Thames waterside areas are detailed further within Appendix A.3: Flood Defence.

An ongoing programme of inspection, maintenance, repair and replacement of defences will be

required in Thurrock in the future (see Appendix A.3). The current Environment Agency estimates of financial investment required to maintain and improve defences to 2050 are as follows;

Fixed flood defences – maintenance and repair £40 million

Fixed flood defences –major repairs and replacements £280 million

Flood barriers and outfalls: £50 million

After 2050 it is anticipated large scale raising of defences will be required based on current sea-level

rise predictions. Any financial investment in Thurrock’s flood defences will be subject to Defra’s Flood

and coastal resilience partnership funding policy statement whereby financial contributions will be

required from partners (including Thurrock Council, Environment Agency, landowners and other key stakeholders) to attract the maximum amount of FCERM funding.

Safeguarding land for future flood protection

Ensuring protection from coastal flooding into the future will mean land must be safeguarded both for

access and maintenance to current defences and to allow for expansion of defence footprints as a

greater degree of protection is required. While most hard defences could be raised within existing

footprints, embankments such as those in the Rainham Policy Unit, parts of East Tilbury and

Shellhaven and Fobbing Marshes Policy Unit north of the Fobbing Horse Barrier would require widening to accommodate increased height.

It must also be considered that whilst hard defences could potentially be raised within existing

footprints, the structures would be tall, unattractive and restrict public access. Additional space will be

needed for construction works and vehicle access during defence-raising. Furthermore, land would be

required for maintaining, replacing and improving flood defences along the Thames. Corridors of land

along existing defence lines need to be safeguarded. Land requirements will vary by site and should be discussed and agreed with the Environment Agency.

An option for a future flood barrier is identified at Long Reach within Thurrock Council’s boundary.

Thurrock Council and the Environment Agency are considering possible options to safeguard land for future construction of the barrier and permanent ‘on-shore’ facilities associated with it.



Areas have also been identified within Thurrock where managed realignment of defences could

achieve landscape, development, public amenity and environmental enhancements. Significant

improvements can be made as part of integrated riverside design. Any such designs must accommodate existing flood defence crest levels and allow for them to be raised in the future.

For further information, reference should be made to the TE2100 Plan which can be found here: https://www.gov.uk/government/publications/thames-estuary-2100-te2100.

3.12.3 Flood Alleviation Schemes

In addition to fluvial and tidal flood defences, a number of flood alleviation schemes have been

completed or are in the appraisal process. These range from localised SuDS schemes, to more strategic regional infrastructure solutions, as listed in Table 3-2.

https://www.gov.uk/government/publications/thames-estuary-2100-te2100



Table 3-2 Thurrock Flood Alleviation Schemes

Flood Alleviation Schemes

Description Status

Tilbury Integrated Flood Strategy

The project was led by Thurrock Council who worked in partnership with AW and the Environment Agency to carry out this study.

Tilbury, Essex, is at risk of flooding thought to be a result of surface water runoff that is unable to drain away adequately. Tilbury is served by separate sewer system with the surface water discharging to the designated ‘Main River’ watercourses which themselves drain into the Thames Estuary either by gravity outfalls or pumps. Consequently, the surface water drainage is vulnerable to flooding when water levels in the designated ‘Main River’ watercourses are elevated. Previous studies have investigated flood risk for the fluvial, surface water and sewer systems, with different parts of the system coming under different ownership, but they interact and affect each other. As a result, the Tilbury catchment required a modelling approach that considered the interaction and interdependencies of the full drainage arrangement to understand the relationship between the different sources of flooding and their response to different rainfall events.

The study objectives were as follows: ─ construct and verify an integrated catchment model of the entire piped and open-channel drainage system in Tilbury;

─ produce flood risk maps for Tilbury for a range of design storms, including an allowance for climate change;

─ produce an operational plan highlighting local drainage problems and concerns;

─ consider outline options appraisal of flood mitigation options for Tilbury in the short, medium and long term; and,

─ produce an action plan setting out the maintenance activities and the flood mitigation options investigated, with timescales and owners for implementation.

This project was completed in 2017. The report identified there was a lack of capacity in the AW sewer system and there was a need to address this. The key recommendation was to the link the eastern and the western sewer network to create additional capacity, helping to reduce surface water flooding at key locations.

Flooding has been reported in the areas within Tilbury which triggered the modelling work, and Thurrock Council are working with Essex County Council to deliver a pilot Property Level Resilience scheme to select properties in the town.

Complete

Pump Street Flood Alleviation Scheme

Properties on Pump St, Horndon on the Hill, had previously recorded internal flooding to 3 properties in 2002/03. After this event significant local drainage and maintenance was undertaken which appeared to alleviate the flooding with only minor recurrences thereafter. Unfortunately in December 2013 and January 2014 internal flooding to 4 properties occurred and persistent garden flooding has occurred on numerous occasions since. Results of an interim s19 flood investigation report into the flooding identified that recent flooding has been caused by out of bank flows from the Pump Street Brook. In times of heavy rainfall the watercourse is unable to get beyond Pump Street due to an undersized culvert, intensified by lack of maintenance to the watercourse downstream, causing an obstruction to flow. A project was delivered and completed in 2015 by Thurrock Council to alleviate surface water flood risk to 4 cottages located along Pump Street at a cost of £4k, £20k of which was contributed from the Anglian Eastern RFCC Local Levy. The 96m-long culvert on Pump Street Brook was upsized to a 300 x 1000mm box culvert and a flood wall installed to the rear curtilage of the properties. The combination of the measures manages flood risk to the properties from a flood with a 1% chance of occurring in any one year including an allowance for an increase in peak flows anticipated due to climate change.

Complete




Description Status

Thames Estuary Asset Management 2100 programme (TEAM2100)

TEAM2100 is the first multi-year programme to be implemented from the TE2100 Plan and is one of the Government’s top 40 infrastructure projects, valued at £308 million. TEAM2100 is a pathfinder programme including new and more efficient ways of working, using a long term contract with a single delivery partner and establishing a co-located, integrated delivery team of Environment Agency and their delivery partner, CH2M.

Current work and planned for 2017/18 within the Thurrock Council area includes the following which totals to approximately £1million: ─ Design work for Flood Gate refurbishment or decommissioning throughout the area;

─ Appraisal of the major drainage outfalls including Mardyke, Stonehouse, West Thurrock Main, Botney and Mucking Sluices;

─ Appraisal and refurbishment of pumps and gravity outfalls at Worlds End Pumping Station, Tilbury;

─ Initial Assessment of tidal defences at Harrisons Wharf, Purfleet;

─ Appraisal of and design work for tidal defences at Tilbury Docks, Cruise Terminal, Fort and Power Station; and,

─ Appraisal of tidal defences at East Tilbury and also Shellhaven.

Due

Stanford-le-Hope Integrated Flood Alleviation Scheme

An initial project led by Thurrock Council appraised various options upstream of Stanford-le-Hope (SLH) to intercept surface water runoff and store/slow water from releasing into the urbanised area of SLH. Modelling identified a range of potential viable options (4). The project ceased to progress to deliver an Outline Business Case (OBC) as Thurrock were unable to secure the necessary funding. The Environment Agency have recently completed an update to the Stanford Brook fluvial catchment model and based upon this evidence base, and the prior work completed by Thurrock Council, are now developing an Integrated Flood Alleviation Scheme to investigate and appraise solutions to manage flood risk to people, property and infrastructure in the catchment from a combination of fluvial and surface water sources. Thurrock Council are in support of this approach, which is included in the FCRM capital investment programme.

Pending

Tilbury Barrier - Dual Function Lock Gate Installation

The Environment Agency are working with the Port of Tilbury on a £14 million project to replace the existing flood defence barrier with a new dual function lock gate at the Port of Tilbury in Essex that will also act as a flood defence. The existing barrier built in1981 forms part of the Thames defences that reduce flood risk to over 9000 homes in the Purfleet, Grays and Tilbury area. The barrier itself protects over 5000 properties. The partnership project with the Port of Tilbury is due to complete in 2019/20.

Due

Linford, Gobians Sewer Surface Water Study

The study, led by Thurrock Council, has been included in the Environment Agency’s Business Case Package. Linford is identified as an area at potential risk from surface water flooding in Thurrock Council’s Surface Water Management Plan (SWMP). On behalf of Thurrock Council, CH2M have carried out an Initial Assessment stage to identify outline flood alleviation options and confirm if there is viability to progress the study into a project. The study is considered multiple sources of potential flood risk, including surface water, fluvial and other contributing factors.

This project was completed in autumn 2017. The outcome of the Initial Assessment stated a low Benefit to Cost ratio, and further work will need to be undertaken to determine the schemes viability.

Complete

Grays Park Surface Water Study

The study, led by Thurrock Council, has been included in the Environment Agency’s Business Case Package. The Grays Park area is identified as an area at potential risk from surface water flooding in Thurrock Council’s Surface water Management Plan (SWMP). The Initial Assessment stage has been completed and has identified there is limited justification to progress the study further at this time. Whilst a positive benefit to cost ratio was identified, further work is required to more accurately determine the viability of the scheme, which proposed to develop a flood storage area within Grays Park. Recommendations from the study have identified the need to collect and verify flood records going forward to further strengthen the case for change and to progress a project. Thurrock Council will take these recommendations forward as well as to work closely with partner authorities to build upon the existing information.

Complete




Description Status

Milehams Yard Scheme

Milehams Yard is a small site allocated to industrial use in Purfleet, Thurrock, located on Tank Hill Road, with Access from New Tank Hill Road, and is bounded by the C2C Purfleet Branch line and HS1. Following earth works to develop the then Channel Tunnel Rail Link (CTRL) now referred to as High Speed 1 (HS1), remedial measures were incorrectly implemented, resulting in surface water unable to drain away sufficiently. Milehams Yard sits at the lowest point, and is therefore susceptible to surface water flooding, as water is unable to drain away into the Mardyke river. Thurrock Council has investigated additional works to help drain water away, and is in the process of determining if the proposed drainage route is viable. Works will also include a twin culvert under A1306 Arterial Road in Purfleet, ditch clearance, and re-profiling of a ditch. To enable drainage into the Mardyke. Cost profiles are in the region of £30k. AECOM has completed preliminary works.

Thurrock Council has investigated the financial viability of making improvements to the Milehams Yard site. Results presented by AECOM has resulted in the scheme no longer becoming viable for the Council to deliver without external assistance. Thurrock Council are reviewing alternative solutions. Cost profiles are currently in the region of £120k.

Ongoing

Property Level Resilience Pilot

Thurrock Council has been in liaison with Essex County Council to expand on their scheme delivering Property Level Resilience to individual homes which have experienced surface water flooding within the dwelling. As this is a pilot study, only a handful of properties have been invited to participate (eight). Homes will be contacted by Essex County Council on Thurrock Council’s behalf, inviting them to participate. A grant of up to £5,000 can be awarded to individual homes to install devices which prevent water from entering the property, such as one-way valves and air bricks, as well as the installation of flood doors. The home will be visited by an auditor to determine what is required, and if the resident agrees, these recommendations will be installed. Where a property is determined to be in a high flood risk area, or the property has been identified by AW as having had surface water flooding in the past, these schemes may be funded by these organisations.

The scheme is expected to be completed by April 2018.

Ongoing



4. Impact of Climate Change

The NPPF and supporting practice guide sets out how the planning system should help minimise

vulnerability and provide resilience to the impacts of climate change. This includes demonstrating

how flood risk will be managed now and over the developments lifetime, taking climate change into account.

In previous SFRAs and site specific Flood Risk Assessments an allowance of 20% was added to the 1% AEP (1 in 100 year) return period to account for increases in flood risk due to climate change.

In February 2016, the Environment Agency published revised guidance on climate change allowances

26 including predictions of anticipated change for:

Peak river flow by river basin district

Peak rainfall intensity

Offshore wind speed and extreme height

The guidance reflects an assessment completed by the Environment Agency between 2013 and 2015

using United Kingdom Climate Projections 2009 (UKCP09) data to produce more representative climate change allowances across England.

4.1 Peak River Flow

Climate change allowances applicable to Thurrock Council (Thames River Basin District) are set out in Table 4.1 below.

Table 4-1 Peak River Flow Allowances for Thames River Basin District

River Basin

District

Allowance

Category

Total potential

change anticipated

for the ‘2020’s

(2015 to 2039)

Total potential

change anticipated

for the ‘2050’s

(2040 to 2069)

Total potential

change anticipated

for the ‘2080’s

(2070 to 2115)

Thames Upper End 25% 35% 70%

Higher Central 15% 25% 35%

Central 10% 15% 25%

4.1.1 Strategic Planning

For the purposes of strategic planning, Thurrock Council will primarily refer to the Environment

Agency Flood Zones 1, 2, 3a and 3b. However, although the Environment Agency Flood Zones are

used as a basis for strategic planning and application of the Sequential Test, the potential impact of

climate change from all sources must be considered throughout the planning process to ensure for

example that a site currently within Flood Zone 2 will not fall into Flood Zone 3 when future climate change is taken into account.

For the purposes of strategic planning and completion of the sequential test, Thurrock Council are

advised to apply the ‘2070 to 2115’ 100 year development lifetime outlined in Table 4-1 relating to

residential development. For more vulnerable, residential development this correlates to a climate change range of impacts of between + 25% and + 70% on the 1% AEP (1 in 100 year) return period.

River Thames - Hydraulic breach modelling along the Thurrock River Thames frontage has been

updated as part of this SFRA update. Flood outlines are based on the 0.5% (1 in 200 year) and 0.1%

(1 in 1000 year) AEP 2116 scenarios, the recommended climate change factors (UKCP09 medium

emissions 95%tile) have been applied to generate the extreme water levels with allowances for sea level rise for the 2116 scenarios.

26





River Mardyke - Hydraulic modelling provided by the Environment Agency for this watercourse was

prepared in 2011 and therefore the climate change projection is based on the +20% climate

allowance. For the purpose of this SFRA the updated climate change allowances have not been

provided. However, in the absence of model outputs for the updated climate change allowances on

the Mardyke, the 1 in 1000 year (0.1%) AEP has been used as a proxy for the 1% (1 in 100 year) plus

climate change for use when mapping climate change flood outlines and completing Sequential

Testing. This approach has been agreed with the Environment Agency. Further details on the method can be found in Appendix H.

The River Mardyke interacts with four main settlements: Bulphan, South Ockenden, Aveley and

Purfleet. Tidal flood defences have a standard of protection up to the 0.1% AEP (1 in 1000 year),

protecting from tidal flood risk from the Thames Estuary. The same standard of protection is not

provided for fluvial flood risks from the Mardyke and there are no formal fluvial defences on the

Mardyke system. Aveley is north of the A13 and therefore is unlikely to be affected by the

watercourse. Bulphan, however, is undefended so there is a potential for climate change to affect this

location. Any development in a flood zone here will require hydraulic modelling to represent climate change within the site-specific FRA to assess the flood risk appropriately.

Stanford Brook - The Environment Agency have recently completed new hydraulic modelling for

Stanford Brook which includes allowances for the new climate change guidance. These extents have been included in mapping of fluvial flooding in Appendix B Map 7A & 7D.

4.2 Peak Rainfall Intensity

Increased rainfall affects river levels and land and urban drainage systems, Table 4-2 below shows

the anticipated changes in extreme rainfall intensity in small and urban catchments. For site specific

flood risk assessments, both the central and upper end allowances should be applied to understand the range of impact.

Table 4-2 Peak rainfall intensity allowance in small and urban catchments (use 1961 to 1990 baseline)

Applies across all of

England

Total potential change

anticipated for the

‘2020s’ (2015 to 2039)


anticipated for the

‘2050s’ (2040 to 2069)


anticipated for the

‘2080s’ (2070 to 2115)

Upper End 10% 20% 40%

Central 5% 10% 20%

4.2.1 Site Specific Flood Risk Assessments

When considering peak river allowances for use in site specific flood risk assessments, the NPPF

flood zone and flood risk vulnerability classification needs to be considered to confirm which range of climate change allowances should be assessed. This is set out in Table 4-3 below.

Tidal Flood Risk including climate change - Appendix C, D & E for breach

modelling mapped results and Appendix J for modelling methodology.



Table 4-3 NPPF Flood Zone and Vulnerability

Flood Zone Vulnerability River Flow Allowances

Flood Zone 2 Essential Infrastructure Higher Central and Upper End

Highly Vulnerable Higher Central and Upper End

More Vulnerable Central and Higher Central

Less Vulnerable Central

Water Compatible None of the allowances

Flood Zone 3a Essential Infrastructure Upper End

Highly Vulnerable Development should not be permitted

More Vulnerable Higher Central and Upper End

Less Vulnerable Central and Higher Central

Water Compatible Central

Flood Zone 3b Essential Infrastructure Upper End

Highly Vulnerable Development should not be permitted

More Vulnerable Development should not be permitted

Less Vulnerable Development should not be permitted

Water Compatible Central

In order to determine which allowance category to use, the development lifetime should be

considered. This should be judged based on the characteristics of development and applicants should be able to justify the chosen lifetime.

Typically:

Residential developments should apply a minimum lifetime of 100 years, unless there is

specific justification for considering a shorter period;

Non- Residential developments should apply a 75 year lifetime.

Therefore, in this locality, if a residential (more vulnerable/100 year lifetime) development were

proposed within Flood Zone 3a an allowance of between 35% and 70% should be applied typically

to the 1% AEP ( 1 in 100 year) to account for the potential impacts of climate change on peak river flows.

As noted above, currently there is no hydraulic modelling available for the River Mardyke that includes

allowances for climate change. Until a time when this data is available, there will be greater emphasis

on site specific FRAs to include additional hydraulic modelling to determine future flood risk to development sites. Reference should be made to Environment Agency Technical Note ‘Thames Area Climate Change Allowance: Guidance for their use in flood risk assessments’.



5. Avoiding Flood Risk – Risk Based Approach to Planning

The NPPF approach aims to ensure that flood risk is considered at all stages of the planning process,

and to avoid inappropriate development in areas of greatest flood risk; steering development towards areas of lower risk.

Development is only permissible in areas at risk of flooding in exceptional circumstances where it can

be demonstrated that there are no reasonably available sites in areas of lower risk, the sustainability

benefits outweigh flood risks and, the development will be safe for its lifetime without increasing flood

risk elsewhere. Such development is required to include mitigation/management measures to minimise risk to life and property should flooding occur.

Building on these principles, the NPPF and Technical Guidance have established a process for the

assessment of flood risk, with each stage building upon the previous assessment with a refinement of

the evidence base. Utilising a Source – Pathway – Receptor approach, the source of flooding, the

spatial distribution of flood risk and the vulnerability of development types are assessed to inform

decision making through each of the key stages of the Flood Risk Management Hierarchy, as outlined in the Technical Guidance and shown in Table 5.1 below.

Table 5-1 Flood Risk Management Hierarchy and the SFRA process

5.1 Sequential Approach

This Section guides the application of the Sequential Test and Exception Test in the plan-making and

planning application processes. Not all development will be required to undergo these tests, as

described below, but may still be required to undertake a site specific FRA, guidance about which is included in Section 7.

The sequential approach is a decision-making tool designed to ensure that sites at little or no risk of

flooding are developed in preference to sites at higher risk. This will help avoid the development of

sites that are inappropriate on flood risk grounds. The subsequent application of the Exception Test

where required will ensure that new developments in flood risk areas will only occur where flood risk is clearly outweighed by other sustainability drivers.

The sequential approach can be applied at all levels and scales of the planning process, both

between and within Flood Zones. All opportunities to locate new developments (except Water

Compatible) in reasonably available areas of little or no flood risk should be explored, prior to any decision to locate them in areas of higher risk.

5.2 Applying Sequential Test – Plan-Making

It should be demonstrated that a range of possible sites have been considered in conjunction with the

Flood Zone and vulnerability information from the SFRA, applying the Sequential Test, and where

necessary, the Exception Test, in the site allocation process. Figure 5.1 illustrates the approach for

applying the Sequential Test that Thurrock Council should adopt in the allocation of sites as part of the

preparation of the Thurrock Local Plan. The Sequential Test should be undertaken by Thurrock Council and accurately documented to ensure decision processes are consistent and transparent



The Sequential Test requires an understanding of the Flood Zones in the study area and the

vulnerability classification of the proposed developments. Flood Zone definitions are provided in

Table 2-2 and mapped in Figure 7, Appendix B (and the Flood Map for Planning (Rivers and Sea) on

the Environment Agency website). Flood risk vulnerability classifications, as defined in the NPPG are presented in Table 5-2.

The flow diagram presented in Figure 5-1 illustrates how the Sequential Test process should be applied to identify the suitability of a site for allocation, in relation to the flood risk classification.

Figure 5-1 Application of the Sequential Test for the Plan Making Process



Table 5-2 Flood Risk Vulnerability Classification (PPG, 2014)

Vulnerability Classification

Development Uses

Essential Infrastructure

Essential transport infrastructure (including mass evacuation routes) which has to cross the area at risk.

Essential utility infrastructure which has to be located in a flood risk area for operational reasons, including electricity generating power stations and grid and primary substations; and water treatment works that need to remain operational in times of flood.

Wind turbines.

Highly Vulnerable Police stations, ambulance stations and fire stations and command centres and telecommunications installations required to be operational during flooding.

Emergency dispersal points.

Basement dwellings.

Caravans, mobile homes and park homes intended for permanent residential use.

Installations requiring hazardous substances consent. (Where there is a demonstrable need to locate such installations for bulk storage of materials with port or other similar facilities, or such installations with energy infrastructure or carbon capture and storage installations, that require coastal or water-side locations, or need to be located in other high flood risk areas, in these instances the facilities should be classified as “essential infrastructure”).

More Vulnerable Hospitals.

Residential institutions such as residential care homes, children’s homes, social services homes, prisons and hostels.

Buildings used for dwelling houses, student halls of residence, drinking establishments, nightclubs and hotels.

Non–residential uses for health services, nurseries and educational establishments.

Landfill and sites used for waste management facilities for hazardous waste.

Sites used for holiday or short-let caravans and camping, subject to a specific warning and evacuation plan.

Less Vulnerable Police, ambulance and fire stations which are not required to be operational during flooding.

Buildings used for shops, financial, professional and other services, restaurants and cafes, hot food takeaways, offices, general industry, storage and distribution, non–residential institutions not included in “more vulnerable”, and assembly and leisure.

Land and buildings used for agriculture and forestry.

Waste treatment (except landfill and hazardous waste facilities).

Minerals working and processing (except for sand and gravel working).

Water treatment works which do not need to remain operational during times of flood.

Sewage treatment works (if adequate measures to control pollution and manage sewage during flooding events are in place).

Water-Compatible Development

Flood control infrastructure.

Water transmission infrastructure and pumping stations.

Sewage transmission infrastructure and pumping stations.

Sand and gravel working.

Docks, marinas and wharves.

Navigation facilities.

MOD defence installations.

Ship building, repairing and dismantling, dockside fish processing and refrigeration and compatible activities requiring a waterside location.

Water-based recreation (excluding sleeping accommodation).

Lifeguard and coastguard stations.

Amenity open space, nature conservation and biodiversity, outdoor sports and recreation and essential facilities such as changing rooms.

Essential ancillary sleeping or residential accommodation for staff required by uses in this category, subject to a specific warning and evacuation plan.



NPPF acknowledges that some areas will (also) be at risk of flooding from sources other than fluvial.

All sources must be considered when planning for new development including: flooding from land or surface water runoff; groundwater; sewers; and artificial Sources.

If a location is recorded as having experienced repeated flooding from the same source this should be acknowledged within the Sequential Test.

Table 5-3 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (PPG, 2014)

Flood Risk Vulnerability Classification

Essential Infrastructure

Highly Vulnerable

More Vulnerable

Less Vulnerable

Water Compatible

Flo

od Z

one

1

2 Exception test Required

3a Exception Test Required

Exception Test Required

3b *1

Exception Test Required*

*

- Development is appropriate - Development should not be permitted

* In Flood Zone 3b (functional floodplain) essential infrastructure that has to be there and has passed

the Exception Test, and water-compatible uses, should be designed and constructed to:

- remain operational and safe for users in times of flood;

- result in no net loss of floodplain storage;

- not impede water flows and not increase flood risk elsewhere.

The recommended steps in undertaking the Sequential Test are detailed below. This is based on the Flood Zone and Flood Risk Vulnerability table and is summarised in Figure 5-1.

5.2.1 Recommended stages for LPA application of the Sequential Test in Plan-Making

The information required to address many of these steps is provided in the accompanying maps

presented in Appendix B. When preparing their Local Plan, a database of the potential allocation

sites across Thurrock Council will be generated and information for each site populated using the GIS

layers presented in maps accompanying this report. This database can be used by Thurrock Council when applying the steps below:

1. Assign potential developments with a vulnerability classification (Table 5-2). Where

development is mixed, the development should be assigned the highest vulnerability class of the developments proposed.

2. The location and identification of potential development should be recorded.

3. The Flood Zone classification of potential development sites should be determined based on

a review of the Flood Map for Planning (Rivers and Sea). Where these span more than one Flood Zone, all zones should be noted, preferably using percentages.

4. The design life of the development should be considered with respect to climate change:

100 years – up to 2117 for residential developments; and

75 years – up to 2092 for commercial / industrial developments, or other time horizon

specific to the non-residential use proposed.

5. Identify existing flood defences serving the potential development sites. However, it should be

noted that for the purposes of the Sequential Test, Flood Zones ignoring defences should be used.



6. Highly Vulnerable developments to be accommodated within the Borough should be located

on those sites identified as being within Flood Zone 1. If these cannot be located in Flood

Zone 1, because the identified sites are unsuitable or there are insufficient sites in Flood Zone

1, sites in Flood Zone 2 can then be considered. If sites in Flood Zone 2 are inadequate then

additional sites in Flood Zones 1 or 2 may need to be identified to accommodate development or opportunities sought to locate the development outside the Borough.

7. Once all Highly Vulnerable developments have been allocated to a development site,

consideration can be given to those development types defined as More Vulnerable. In the

first instance More Vulnerable development should be located on sites in Flood Zone 1.

Where these sites are unsuitable or there are insufficient sites remaining, sites in Flood Zone

2 can be considered. If there are insufficient sites in Flood Zone 1 or 2 to accommodate More

Vulnerable development, sites in Flood Zone 3a can be considered. More Vulnerable developments in Flood Zone 3a will require application of the Exception Test.

8. Once all More Vulnerable developments have been allocated to a development site,

consideration can be given to those development types defined as Less Vulnerable. In the

first instance Less Vulnerable development should be located on sites in Flood Zone 1,

continuing sequentially with Flood Zone 2, then 3a. Less Vulnerable development types are not appropriate in Flood Zone 3b – Functional Floodplain.

9. Essential Infrastructure that has to be there is appropriate in FZ3b however, alternative options should always be considered first.

10. Water Compatible development has the least constraints with respect to flood risk and it is

considered appropriate to allocate these sites last. The sequential approach should still be

followed in the selection of sites; however it is appreciated that Water Compatible development by nature often relies on access and proximity to water bodies.

11. On completion of the Sequential Test, consideration will be given to the risks posed to a site

within a Flood Zone in more detail as part of the Level 2 SFRA. By undertaking the Exception

Test, this more detailed study should consider the detailed nature of flood hazard to allow a

sequential approach to site allocation within a Flood Zone. Consideration of flood hazard within a flood zone would include:

a. flood risk management measures,

b. the rate of flooding,

c. flood water depth,

d. flood water velocity.

e. Windfall Sites

12. Windfall sites are those which have not been specifically identified as available in the Local

Plan process. In cases where development needs cannot be fully met through the provision

of site allocations, a realistic allowance for windfall development should be assumed, based

on past trends. It is recommended that the acceptability of windfall applications in flood risk

areas should be considered at the strategic level through a policy setting out broad locations

and quantities of windfall development that would be acceptable or not in Sequential Test terms.

5.3 Applying Sequential Test – Planning Applications

It is necessary for developers to undertake a sequential test for a planning application if both of the following apply:

1. The proposed development is in Flood Zone 2 or 3.

2. A sequential test hasn’t already been completed for a development of the type you plan to carry out on your proposed site (check with Thurrock Council).

http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change/flood-zone-and-flood-risk-tables/table-1-flood-zones/



The Environment Agency publication ‘Demonstrating the flood risk Sequential Test for Planning

Applications27

’ sets out the procedure for applying the sequential test to individual applications as follows:

Identify the geographical area of search over which the test is to be applied; this could be the

Borough area, or a specific catchment if this is appropriate and justification is provided (e.g. school catchment area or the need for affordable housing within a specific area).

Identify the source of ‘reasonably available’ alternative sites; usually drawn from evidence

base / background documents produced to inform the Local Plan.

State the method used for comparing flood risk between sites; for example the Environment

Agency Flood Map for Planning, the SFRA mapping, site-specific FRAs if appropriate, other mapping of flood sources.

Apply the Sequential Test; systematically consider each of the available sites, indicate

whether the flood risk is higher or lower than the application site, state whether the alternative

option being considered is allocated in the Local Plan, identify the capacity of each alternative site, and detail any constraints to the delivery of the alternative site(s).

Conclude whether there are any reasonably available sites in areas with a lower probability of flooding that would be appropriate to the type of development or land use proposed.

Where necessary, as indicated Table 5-3, apply the Exception Test.

Apply the Sequential approach to locating development within the site.

Ultimately, after applying the Sequential Test, Thurrock Council (taking advice from the Environment

Agency) needs to be satisfied in all cases that the proposed development would be safe and not lead

to increased flood risk elsewhere. This needs to be demonstrated within a FRA and is necessary regardless of whether the Exception Test is required.

5.3.1 Sequential Test Exemptions

It should be noted that the Sequential Test does not need to be applied in the following circumstances:

Individual developments proposed on sites which have been allocated in development plans

through the Sequential Test.

Minor development, which is defined in the NPPF as:

o Minor non-residential extensions: industrial / commercial / leisure etc. extensions with a footprint <250m

2.

o Alterations: development that does not increase the size of buildings e.g. alterations to external appearance.

o Householder development: for example; sheds, garages, games rooms etc. within the

curtilage of the existing dwelling, in additional to physical extensions to the existing

dwelling itself. This definition excludes any proposed development that would create

a separate dwelling within the curtilage of the existing dwelling e.g. subdivision of houses into flats.

Change of Use applications, unless it is for a change of use of land to a caravan, camping or

chalet site, or to a mobile home site or park home site.

Development proposals in Flood Zone 1 (land with a low probability of flooding from rivers or

the sea) unless the SFRA, or other more recent information, indicates there may be flooding issues now or in the future (for example, through the impact of climate change).

27

Environment Agency, April 2012, ‘Demonstrating the flood risk Sequential Test for Planning Applications’, Version 3.1



Redevelopment of existing properties (e.g. replacement dwellings), provided they do not

increase the number of dwellings in an area of flood risk (i.e. replacing a single dwelling within an apartment block).

5.4 Exception Test

The purpose of the Exception Test is to ensure that, following the application of the Sequential Test,

new development is only permitted in Flood Zone 2 and 3 where flood risk is clearly outweighed by

other sustainability factors and where the development will be safe during its lifetime, considering climate change.

The Exception Test provides a method of managing flood risk while still allowing necessary

sustainable development to occur. The test is only appropriate for use when there are large areas in

Flood Zones 2 and 3a where the Sequential Test alone cannot deliver acceptable sites, but where

some continuing development is necessary for wider sustainable development reasons. The flow

chart presented in Figure 5-1 demonstrates the methodology to determine whether an Exception Test is required for proposed site allocations.

In order to pass the Exception Test, the NPPF Technical Guidance identifies two elements that need to be demonstrated/fulfilled to the satisfaction of the LPA:

1. The development provides wider sustainability benefits to the community that outweigh flood risk, informed by a SFRA where one has been prepared; and

2. A site-specific flood risk assessment (FRA) must demonstrate that the development will be

safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, reducing flood risk overall.

Satisfying the Exception Test involves consideration of the reasons behind the selection of the site for

development, from the sustainability appraisal, as well as consideration in planning and design, such that the site will remain safe and operational in the event of flooding. This may involve demonstrating:

A sequential approach is taken to development site layout, such that within the site, the most

vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location:

Buildings are designed to be appropriately flood resilient and resistant, with essential services

remaining functional in the event of flooding, and quick recovery following a flood;

Provision of safe means of access and egress during a flood event;

Emergency evacuation procedures are developed, to be utilised following receipt of a flood warning;

Priority is given to the use of sustainable drainage systems

In considering this, breach modelling results included within this SFRA should be taken into account

to determine the variation in flood depth and hazard within Flood Zone 3a. This will confirm whether more appropriate locations maybe available within Flood Zone 3a, with a lower hazard rating.



6. Managing and Mitigating Flood Risk through Spatial

Planning and Development Management

6.1 Overview

The NPPF appreciates that it may not always be possible to avoid locating development in areas at

risk of flooding. This section builds on the findings of the SFRA to provide guidance on the range of

measures that could be considered on site in order to manage and mitigate flood risk. These

measures should be considered when preparing a site-specific FRA as described in Section 7.1 Appendix A outlines the recommendations for policy and practice that Thurrock Council should adopt

in relation to flood risk planning policy and development management decisions.

6.2 Development Layout and Sequential Approach

Flood risk should be considered at an early stage in deciding the layout and design of a site to provide

an opportunity to reduce flood risk within the development. Most large development proposals

include a variety of land uses of varying vulnerability to flooding. The sequential approach should be

applied within development sites to locate the most vulnerable elements of a development in the

lowest risk areas (considering all sources of flooding) e.g. residential elements should be restricted to

areas at lower probability of flooding whereas parking, open space or proposed landscaped areas can

be placed on lower ground with a higher probability of flooding. Reference should be made to breach

modelling included within this study to provide further detail of fluvial and tidal flood risk within Flood Zones.

6.3 Finished Floor Levels

Where developing in Flood Zone 2 and 3 is unavoidable, the recommended method of mitigating flood

risk to people, particularly with More Vulnerable (residential) and Highly Vulnerable land uses, is to ensure internal floor levels are raised a freeboard level above the design flood level.

In certain situations (e.g. for proposed extensions to buildings with a lower floor level or conversion of

existing historical structures with limited existing ceiling levels), it could prove impractical to raise the

internal ground floor levels to sufficiently meet the general requirements. In these cases, the

Environment Agency and/or Thurrock Council should be approached to discuss options for a

reduction in the minimum internal ground floor levels provided flood resistance measures are implemented up to an agreed level.

There are also circumstances where flood resilience measures should be considered first. These are

described further below. For both Less and More Vulnerable developments where internal access to

higher floors is required, the associated plans showing the access routes and floor levels should be included within any site-specific FRA.

A sequential approach to site planning should be applied within new development sites

For the purposes of informing a site specific FRA, More Vulnerable and Highly

Vulnerable development within Flood Zones 2 and More Vulnerable development within

Flood Zones 3 should set Finished Floor Levels 300mm above the known or modelled

1% AEP (1 in 100 year) fluvial flood level and 0.5% AEP (1 in 200 year) tidal flood level

inclusive of climate change. For more vulnerable single-storey uses, ground floor

levels should be provided 300mm above the 0.1% AEP (1 in 1000 year) flood level, inclusive of climate change.



6.4 Safe Access/ Egress

Safe access and egress is required to enable the evacuation of people from the development, provide

the emergency services with access to the development during times of flood and enable flood defence authorities to carry out any necessary duties during periods of flood.

A safe access/egress route should allow occupants to safely enter and exit the buildings and be able

to reach land outside the flooded area (e.g. within Flood Zone 1) using public rights of way without the

intervention of emergency services or others during design flood conditions, including climate change allowances.

In all these cases, a ‘dry’ access/egress is a route located above the 1% AEP flood level (1 in 100 year) including an allowance for climate change.

6.5 Safe Refuge

In exceptional circumstances, dry access above the 0.1% AEP (1 in 100 year) fluvial flood level

including climate change and 0.5% AEP (1 in 200 year) tidal flood level including climate change may

not be achievable. In these circumstances the Environment Agency and Thurrock Council should be

consulted to ensure that the safety of the site occupants can be satisfactorily managed. This will be

informed by the type of development, the number of occupants and their vulnerability and the flood

hazard along the proposed egress route. For example, this may entail the designation of a safe place

of refuge on an upper floor of a building, from which the occupants can be rescued by emergency

services. It should be noted that sole reliance on a safe place of refuge is a last resort, and all other

possible means to evacuate the site should be considered first. Provision of a safe place of refuge will not guarantee that an application will be granted.

6.6 Surface Water Management

Sustainable Drainage Systems (SuDS) should be used to reduce and manage surface water runoff to

and from proposed developments as near to source as possible in accordance with the requirements

of the Technical Standards and supporting guidance published by DCLG and Department for the

Environment, Food and Rural Affairs (DEFRA)28.

In line with the Thurrock Council Core Strategy,

SuDS must be implemented for sites in Flood Zone 2 and 3. SuDS must be considered for sites in Flood Zone 1.

28

Sustainable drainage systems: non-statutory technical standards - https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory-technical-standards; PPG Flood Risk and Coastal Change - http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change/reducing-the-causes-and-impacts-of-flooding/why-are-sustainable-drainage-systems-important/

All major developments and other development should not result in an increase in

surface water runoff, and where possible, should demonstrate betterment in terms of rate and volumes of surface water runoff.

For developments located in areas at risk of fluvial and tidal flooding safe access / egress must be provided for new development as follows in order of preference:

Safe dry route for people and vehicles.

Safe dry route for people.

If a dry route for people is not possible, a route for people where the flood hazard

(in terms of depth and velocity of flooding) is low and should not cause risk to people.

If a dry route for vehicles is not possible, a route for vehicles where the flood

hazard (in terms of depth and velocity of flooding) is low to permit access for emergency vehicles. However the public should not drive vehicles in floodwater.

https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory-technical-standards

https://www.gov.uk/government/publications/sustainable-drainage-systems-non-statutory-technical-standards



6.7 Recommendations for Policy and Practice

Further recommendations for policy and practice across Thurrock Council are contained within Appendix A of this report including:

Strategic planning;

Development management;

Emergency planning;

Flood Defences, and;

SuDS.



7. Guidance for Developers

7.1 What is a Flood Risk Assessment?

A site-specific FRA is a report suitable for submission with a planning application which provides an

assessment of flood risk to and from a proposed development, and demonstrates how the proposed

development will be made safe, will not increase flood risk elsewhere and where possible will reduce

flood risk overall in accordance the NPPF/PPG and Thurrock’s Core Strategy adopted in 201529

. A

FRA must be prepared by a suitably qualified and experienced person and must contain all the information needed to allow Thurrock Council to satisfy itself that policy requirements have been met.

7.2 When is a Flood Risk Assessment required?

The NPPF states that a site-specific FRA is required in the following circumstances:

Proposals for new development (including minor development30

and change of use) in Flood

Zones 2 and 3.

Proposals for new development (including minor development and change of use) in an area

within Flood Zone 1 which has critical drainage problems (as notified to the LPA by the Environment Agency)

31.

Proposals of 1 hectare or greater in Flood Zone 1.

Where proposed development or a change of use to a more vulnerable class may be subject to other sources of flooding.

7.3 How detailed should a FRA be?

The PPG states that site-specific FRAs should be proportionate to the degree of flood risk, the scale

and nature of the development, its vulnerability classification and the status of the site in relation to

the Sequential and Exception Tests. Site-specific FRAs should also make optimum use of readily

available information, for example the mapping presented within this SFRA and available on the

Environment Agency website, although in some cases additional modelling or detailed calculations will need to be undertaken

Table 7-1 presents the different levels of site-specific FRA as defined in the CIRIA publication C62432

32 and identifies typical sources of information that can be used.

29

Thurrock Council (2015) Core Strategy and Policies for Management of Development 30

According to the PPG, minor development means: minor non-residential extensions: industrial / commercial / leisure etc. extensions with a footprint <250m

2.

alterations: development that does not increase the size of buildings e.g. alterations to external appearance. householder development: for example; sheds, garages, games rooms etc. within the curtilage of the existing dwelling, in addition to

physical extensions to the existing dwelling itself. This definition excludes any proposed development that would create a separate dwelling within the curtilage of the existing dwelling e.g. subdivision of houses into flats 31

There are no critical drainage areas / problems as notified by the Environment Agency within Thurrock Council at the time of writing- this position should be reviewed by applicant when submitting FRAs. 32

CIRIA, 2004, Development and flood risk – guidance for the construction industry C624.



Table 7-1 Levels of Site-Specific Flood Risk Assessment

Description

Level 1 Screening study to identify whether there are any flooding or surface water management issues related

to a development site that may warrant further consideration. This should be based on readily available existing

information. The screening study will ascertain whether a FRA Level 2 or 3 is required.

Typical sources of information include:

Thurrock Council SFRA

Flood Map for Planning (Rivers and Sea)

Environment Agency Standing Advice

NPPF Tables 1, 2 and 3

Level 2 Scoping study to be undertaken if the Level 1 FRA indicates that the site may lie within an area that is at

risk of flooding, or the site may increase flood risk due to increased run-off. This study should confirm the

sources of flooding which may affect the site. The study should include:

An appraisal of the availability and adequacy of existing information;

A qualitative appraisal of the flood risk posed to the site, and potential impact of the development on flood risk elsewhere; and

An appraisal of the scope of possible measures to reduce flood risk to acceptable levels.

The scoping study may identify that sufficient quantitative information is already available to complete a FRA

appropriate to the scale and nature of the development.

Typical sources of information include those listed above, plus:

Local policy statements or guidance.

Thames Catchment Flood Management Plan.

Data request from the Environment Agency to obtain result of existing hydraulic modelling studies relevant to the site and outputs such as maximum flood level, depth and velocity.

Consultation with EA/Thurrock/sewerage undertakers and other flood risk consultees to gain information and to identify in broad terms, what issues related to flood risk need to be considered including other sources of flooding.

Historic maps.

Walkover survey to assess potential sources of flooding, likely routes for floodwaters, the key features on the site including flood defences, their condition.

Site survey to determine general ground levels across the site, levels of any formal or informal flood defences

Level 3 Detailed study to be undertaken if a Level 2 FRA concludes that further quantitative analysis is required

to assess flood risk issues related to the development site. The study should include:

Quantitative appraisal of the potential flood risk to the development;

Quantitative appraisal of the potential impact of the development site on flood risk elsewhere; and

Quantitative demonstration of the effectiveness of any proposed mitigations measures.

Typical sources of information include those listed above, plus:

Detailed topographical survey.

Detailed hydrographic survey.

Site-specific hydrological and hydraulic modelling studies which should include the effects of the proposed development.

Monitoring to assist with model calibration/verification.

Continued consultation with the LPA, Environment Agency and other flood risk consultees.



7.4 What needs to be addressed in a Flood Risk Assessment?

The PPG states that the objectives of a site-specific flood risk assessment are to establish:

Whether a proposed development is likely to be affected by current or future flooding from

any source;

Whether it will increase flood risk elsewhere;

Whether the measures proposed to deal with these effects and risks are appropriate;

The evidence for the local planning authority to apply (if necessary) the Sequential Test, and;

Whether the development will be safe and pass the Exception Test, if applicable.

Flood Risk Assessment Checklist

Appendix I provides a checklist for site-specific FRAs including the likely information that will likely

need to be provided along with references to sources of relevant information. The exact level of detail

required under each heading will vary according to the scale of development and the nature of the flood risk.

7.5 Pre-application Advice

At all stages, Thurrock Council, and where necessary the Environment Agency and/or the Statutory

Water Undertaker may need to be consulted to ensure the FRA provides the necessary information to fulfil the requirements for planning applications.

The Environment Agency and Thurrock Council each offer pre-application advice services which should be used to discuss particular requirements for specific applications.

Thurrock Council: https://www.thurrock.gov.uk/pre-application-advice/apply-for-pre-application-advice

Environment Agency:

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/297018/LIT_9015_c2822b

.pdf

The following government guidance sets out when LPAs should consult with the Environment Agency on planning applications https://www.gov.uk/flood-risk-assessment-local-planning-authorities.

https://www.gov.uk/flood-risk-assessment-local-planning-authorities



8. Summary

8.1 Overview

The NPPF and accompanying Guidance emphasise the responsibility of LPAs to ensure that flood risk

is understood and managed effectively and sustainably throughout all stages of the planning process.

This SFRA aims to facilitate this process by identifying the spatial variation in flood risk across the

Borough, allowing an area-wide comparison of future development sites with respect to flood risk considerations.

The study area is bounded to the South by the River Thames and to the East by Vange Creek. There

are two other significant Main Rivers in the Borough: Stanford Brook and the River Mardyke, in

addition to a vast network of Ordinary Watercourses including those associated with the Tilbury Flood

Storage Area. Whilst the tidal Thames poses a potential risk of flooding to the Borough, the TTD

provide a substantial standard of protection, up to the 1% AEP (1 in 1000 year event) for the majority

of the Thames frontage. This includes linear walls, flood gates and barriers upstream of connecting

tributaries. The standard of protection offered to the Mardyke and Stanford Brook catchments is

slightly lower in the upper reaches which are proportionate to the amount of urban development in the surrounding areas.

A potential risk of flooding from other (non-river related) sources exists throughout the Borough,

including sewer surcharge, and surface water flooding as a result of heavy rainfall and limited

capacity of drainage infrastructure. Geological indicators also suggest that certain areas of the

Borough may be susceptible to elevated groundwater levels, which may additionally interact with and

exacerbate these sources of flood risk. It is expected that changing climate patterns will have a substantial impact on the level of flood risk from all sources within the Borough.

This SFRA identifies the floodplain areas associated with the River Thames, River Mardyke and

Stanford Brook and presents Flood Zone Maps that delineate the flood zones outlined in the NPPF.

These maps provide the necessary information to facilitate the NPPF risk-based approach to

planning. This process determines the compatibility of various types of development within each flood zone, subject to the application of the Sequential Test and the Exception Test when required

Given the position of the Borough adjacent to the River Thames, it is highly reliant on the TTD system.

Ongoing maintenance of these defences is critical, and priority should be given to safeguarding the standard of protection provided by defences over the lifetime of any development.

It is further recommended that policy options are expanded to include greater emphasis on floodplain

management to complement flood defence infrastructure, by promoting appropriate use of the

floodplain and making space for water. Existing corridors of land along the river frontage should be

safeguarded and opportunities taken to set back development to enable sustainable and cost effective

flood risk management, including upgrading of river walls and embankments. Flood awareness and

robust emergency planning and response will additionally be critical to sustainable ongoing flood risk management.



Appendix A Recommendations for Policy and Practice

Adopting a holistic approach to flood risk management should help ensure that flooding is taken into

account at all stages of the planning process. To aid this holistic approach, it is recommended that all

key recommendations set out in this report are considered and incorporated into the emerging Thurrock Local Plan.

Thurrock is bordered by the River Thames and is therefore highly reliant on flood defences. Where

these defences protect valuable assets ongoing maintenance of these defences is critical, and priority

should be given to safeguarding the standard of protection provided by defences over the lifetime of

any development. However, redevelopment rates along the waterfront in some areas of the Borough

are very high and may additionally offer the opportunity to reduce the current risk and the reliance on

flood defences. This includes making the urban environment more resilient and with a layout that

offers added options for managing future flood risk and the impacts of climate change. As such, it is

recommended that policy options are expanded to include greater emphasis on active floodplain

management, in addition to flood defence maintenance. This may include promoting more appropriate

use of floodplain areas (Flood Zone 3), making space for water, improved flood preparedness and enhanced emergency planning and response measures.

Whilst in other areas along the Thames water front, such as Fobbing Marshes, the alternative action

is to maintain flood defences at their current level accepting the likely consequences of flood increase

as a result of climate change. In some cases it may be appropriate to completely remove flood

defences, for example, the Fobbing Horse Barrier, and allow the surrounding marshes to become

more brackish, hence supporting natural change. This form of floodplain management is known as

managed realignment and is planned at Mucking in association with the new London Gateway Port to create replacement intertidal saltmarshes.

A.1 Strategic Planning

When considering strategic spatial planning across the Borough, flood risk should be an early and

primary consideration. A sequential approach should be taken to allocating strategic development

areas in regions of lowest flood risk, taking into account vulnerability of land use. Consideration

should also be given to strategic allocation of open space and preserving and expanding river corridors to create space for flooding to be managed effectively.

In particular, the following specific recommendations are made:

Ensure the Sequential Test is undertaken for all strategic land allocations and check that the

vulnerability classification of the proposed land use is appropriate to the Flood Zone classification;

Pursue potential opportunities to move existing development from within the floodplain to

areas with a lower risk of flooding. This should include consideration of the vulnerability of

existing developments and whether there is potential for land swap with lower vulnerability uses.

Identify opportunities to create space for water through appropriate location, layout and

design of development, in order to accommodate climate change and assist in managing

future flood risk. This can be achieved by restoring floodplain and flood flow pathways and by

identifying, allocating and safeguarding open space for storage. Equally, existing flood

storage areas should be identified, conserved and protected against loss through redevelopment.

Safeguard existing corridors of land along the River Thames, River Mardyke, Stanford Brook

and tributaries and promote the setting back of development to enable sustainable and cost

effective flood risk management, including upgrading of river walls and embankments. As a

minimum, an 8 m and 16 m buffer strip should be maintained along fluvial and tidal river corridors, respectively.

Promote managed realignment or set back defences and improve the riverside frontage to

provide amenity space and environmental enhancement. A combination of defence



realignment and floodplain management could reduce the impact of flooding to existing

properties and other assets located in the floodable areas on the river side of realigned defences (similar to the approach used around the Tate Modern at Bankside).

The consultation and initial investigation associated with detailed site specific flood risk

assessments should be undertaken at an early stage for major development locations to

ensure opportunities to reduce flood risk are identified early and maximised wherever possible.

Ensure that developments at residual risk of flooding are designed to be flood compatible

and/or flood resilient and maximise the use of open spaces within these developments to

make space for water during times of flooding. Opportunities should be sought to identify a

safe route for any exceedance flow of floodwaters and a suitable storage or discharge location, to avoid any risk to people.

Strategic development allocations should specifically consider the issues of water supply and

drainage infrastructure to service development proposed, taking into account regional

constraints. An early and integrated approach should be taken to holistically assessing and

planning for the flood risk, water supply and drainage requirements and constraints in these

areas. This is likely to be an issue of particular importance in growth areas where limited drainage capacity may create challenges for strategic development.

A.2 Development Management

In consulting on and determining development applications, Thurrock Council must ensure that all

new developments have considered flood risk management from the planning stage. In general, this means that:

Development is located in the lowest risk area where possible;

New development is flood-proofed to a satisfactory level/standard and does not increase flood

risk elsewhere; and

Surface water is managed effectively on site using the SuDS hierarchy and the latest

guidance and best practice.

When a proposed development is located within an area perceived to be at risk of flooding, then a

suitably detailed FRA should determine the actual level of risk to the development and identify options

to mitigate the flood risk to the development, site users and surrounding area. In particular,

development located adjacent to flood defences is required to demonstrate that these defences will

be safe over the lifetime of the development. The requirements for site specific flood risk assessments

and their contents are further detailed in Chapter 5. Planning applications should be considered and

assessed in line with the sequential approach detailed in Section 5.1. Specific recommendations and considerations for development planning are provided below:

If development is to be constructed with less vulnerable uses on the ground level, conditions

need to be put in place to prevent future alteration of these areas to ‘more vulnerable’ uses without further consideration of the associated flood risk.

Single storey residential dwellings or flats should not be considered in high flood risk areas as

they offer no opportunity for safe refuge.

NPPF does not permit basement dwellings to be located within Flood Zone 3a, and as such

these should not be permitted in any areas at risk of flooding. This would include the excavation of basements under existing dwellings.

A safe means to escape via internal access to higher floors 300mm above the 1% annual

probability (1 in 100 year) flood level including an allowance for climate change should be provided for all basement dwellings.

Basement development may affect groundwater flows, and even though the displaced water

will find a new course around the area of obstruction this may have other consequences for

nearby receptors e.g. buildings, trees. Emerging evidence shows that even where there are a



number of consecutively constructed basement developments, the groundwater flows will find a new path.

Residual flood risk should be managed through emergency planning, site design and

protection measures. The key residual flood risks within Thurrock are the overtopping or breach of the River Thames.

Where development within flood risk areas is necessary due to wider

sustainability/regeneration objectives, flood resistance and resilience practices should be followed in the construction and operation of the buildings to minimise the impact of flooding.

Finished floor levels of all residential accommodation should be raised above the 1 in 100

years (1% AEP) plus Climate Change and 1 in 200 year (0.5% AEP) plus Climate Change

defended level, with an allowance for freeboard (300 mm). For properties within the tidal flood

zone associated with the River Thames, floor levels should be above the anticipated 2100

breach levels. For properties associated with the flood zone of the River Mardyke and

Stanford Brook, floor levels should be raised above the 1 in 100 year flood level, taking into

account the updated climate change allowances. Potential access and egress routes should

also be considered and recommendations made for emergency response by occupants in the event of a breach occurring.

Flood risk from all sources should be considered when identifying the perceived level of flood

risk affecting a site. Robust consideration of surface water flood risk is particularly important in

certain regions of the Borough, particularly in the low-lying flat regions, which can be below sea level in places making surface drainage more difficult.

Existing flood storage areas within development areas should be identified, conserved and protected against loss through redevelopment.

An 8 m and 16 m buffer strip should be maintained along fluvial and tidal river corridors,

respectively, to ensure maintenance of the channel can be undertaken. As such, any new

development should be avoided in existing buffer areas. A pragmatic approach should be

adopted for existing development in these areas and opportunities pursued for small scale set

back of development from river walls to enable these structures to be modified, raised and maintained as needed.

For developments adjacent the River Thames, particular consideration should be given to

facilitating the recommendations of the TE2100 plan and Thames CFMP in maintaining, enhancing and replacing flood defences, and safeguarding riverside land.

A.3 Flood Defences

The TE2100 plan has highlighted four action zones and four policy units within Thurrock, which includes two policies:

P4: to take further action to keep up with climate and land use change so that flood risk does not increase.

P3: to continue with existing or alternative actions to manage flood risk. Flood defences will be

maintained at their current level, accepting that the likelihood and/or consequences of a flood will increase because of climate change.

In order to abide with P4 and keep up apace climate change it will be necessary to maintain and

improve flood defences in some areas. This should be done by those responsible for maintaining

flood defences in that area (i.e. riparian land owners, EA). Any development located adjacent to flood

defences is required to demonstrate that these defences will be safeguarded and maintained over the lifetime of the development.

In particular, the future sustainability of the Borough is dependent to a large degree upon the retention

and ongoing maintenance of the TTD infrastructure. However, decisions surrounding investment of

this nature in future years cannot be predicted with any certainty. Additionally, the exact impact of

climate change, and the interaction of the resulting hydrological effects with operational and wider



issues is still uncertain. Consequently other means of reducing the risk of fluvial flooding from the

River Thames may have to be sought in the future. It is therefore imperative that planning decisions

are taken with a clear understanding of the potential risks posed to property and life should things

ultimately go wrong. As such, redevelopment must ensure that residual flood risk is reduced in areas benefiting from flood defence measures through prevention and effective mitigation.

As discussed, management of defences within the Borough will include routine inspection,

maintenance, repair and replacement, in addition to eventual raising of levels in specified areas to

allow for the impact of climate change. Defences along the Thames will need to be raised by up to 0.5

m before 2065 and an additional 0.5 m before 2100. However, raising the level of defences on the

current footprint may introduce visual barriers and will not achieve any wider sustainability objectives.

Therefore, opportunities should be pursued for subsequent improvement of the riverside through

integrated design, considering public access and connectivity, amenity, landscaping and environmental enhancement.

As such, where fluvial defences require replacement, consideration should be given to flood defence

adaptation rather than like-for-like replacement, utilising a combination of flood storage, river defences and floodplain attenuation.

Where new development is proposed adjacent to the TTD, consideration should be given to the

specific recommendations of the TE2100 plan, in requiring reduction of current and future flood risk through:

Raising existing flood defences to the required levels in preparation for future climate

change impacts or otherwise demonstrate how tidal flood defences can be raised in the future, through submission of plans and cross-sections of the proposed raising;

Demonstrating the provision of improved access to existing flood defences and

safeguarding land for future flood defence raising and landscape, amenity and habitat improvements;

Maintaining, enhancing or replacing flood defences to provide adequate protection for the lifetime of the development;

Where opportunities exist, re-aligning or setting back flood defence walls and improving the

river frontage to provide amenity space, habitat, access and environmental enhancements; and

Securing financial contributions towards the anticipated costs of flood risk management

infrastructure required to protect the proposed development over its lifetime.

In more general consideration of flood risk management infrastructure, local policy should continue to

maintain and expand assets that are effective in managing current and future flood risk and promote wider sustainability.

A.4 Sustainable Drainage Systems

Developers, designers and consultants looking for information on how to design SuDS within Thurrock should refer to the Essex SuDS Design Guide

33 for guidance on surface water drainage schemes.

The following documents will also provide advice on how best to design sustainable drainage schemes in Thurrock:

Non-statutory technical standards for sustainable drainage systems

The CIRIA SuDS Manual (C753)

BS8582 Code of practice for surface water management for development sites.

As the LLFA, Thurrock Council specifies34

that planning applications should include a detailed drainage design for all major development proposals, including:

33

http://www.essex.gov.uk/Environment%20Planning/Environment/local-environment/flooding/View-It/Documents/suds_design_guide.pdf

http://www.essex.gov.uk/Environment%20Planning/Environment/local-environment/flooding/View-It/Documents/suds_design_guide.pdf

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/415773/sustainable-drainage-technical-standards.pdf

http://www.ciria.org/Memberships/The_SuDs_Manual_C753_Chapters.aspx

http://shop.bsigroup.com/ProductDetail/?pid=000000000030253266



10 or more houses

A site over 0.5 hectares where the number of houses is unknown

A building greater than 1000 square metres

A site over 1 hectare

Planning applications including those requiring drainage information should be submitted to Thurrock

Council (LPA) with all the relevant documentation. Any drainage information submitted as part of any

outline or full planning application should comply with the Essex County Council checklists for outline drainage design and detailed drainage design, outlined below.

The following checklists should be completed by the applicant and submitted as part of the relevant

planning application in order to demonstrate that the necessary information has been supplied to

assess the suitability of the proposed sustainable drainage system, in line with Paragraphs 103 and 109 of the National Planning Policy Framework (NPPF).

Failure to provide any of the information requested below may result in the Lead Local Flood Authority

(LLFA) making recommendation for refusal of the planning application on grounds of insufficient information.

Outline drainage design checklist

1. Demonstrate an understanding of the natural drainage characteristics within and adjoining the site.

2. Provide an outline assessment of existing geology, ground conditions and permeability through

desk-based research e.g. a review of geology maps and catchment information and site visit observations. Infiltration tests should be carried out at this stage wherever possible.

3. Prepare a Conceptual Drainage Plan to show the above together with:

A. The proposed 'management train'

B. Indicative location and type of source control

C. Site controls with storage locations

D. Conveyance and exceedance routes

E. The destination of runoff.

4. Provide a Conceptual SuDS Design Statement describing:

A. The SuDS Design Criteria applicable to the site

B. Reasoning for inclusion of the selection of SuDS features

C. Indicative runoff rate calculations and attenuation volumes for the lifetime of the development

D. Integration with landscape design

E. Any phasing plan for the development

F. Management of health and safety risks

G. Explanation of land use decision and how they impact drainage

H. Proposed method of flow control

34

http://flood.essex.gov.uk/new-development-advice/how-to-design-suds-in-essex/



I. Information regarding the proposed treatment stages to be applied to each element of the site

J. Demonstration that surface water/groundwater entering the development from adjacent land has been taken into account.

For further advice about the information requested in this checklist please contact Essex County Council using the following email address [email protected].

Detailed drainage design checklist

1. An assessment of suitability for infiltration based on soil types and geology, which should account for:

A. The presence of constraints that must be considered prior to planning infiltration SuDS

B. The drainage potential of the ground

C. Potential for ground instability when water is infiltrated

D. Potential for deterioration in groundwater quality as a result of infiltration.

Evidence of infiltration tests, particularly at the location of any intended infiltration device, and groundwater level monitoring is also required.

2. A Detailed Drainage Plan identifying:

A. The proposed ‘management train’ and total land take

B. Location and type of source control

C. Site controls with storage locations

D. Conveyance and exceedance flow routes

E. The destination of runoff and any runoff rate restrictions

3. A Detailed SuDS Design Statement covering:

A. Final SuDS to be incorporated and final discharge points where relevant

B. How the drainage design satisfies SuDS techniques in terms of water quality and attenuation and discharge quantity for the lifetime of the development

C. Proposals, where relevant, for integrating the drainage system into the landscape or required publicly accessible open space and providing habitat and social enhancement

D. Calculations showing the pre- and post-development peak runoff flow rate for the critical rainfall event.

E. Description of overland flow routes and safeguarding of properties from flooding

F. Management of health and safety risks in relation to feature design.

G. The process for information delivery and community engagement to relevant stakeholders

H. System valuation (including capital costs, operation and maintenance costs, cost contributions) and a demonstration of long term economic viability

I. Provision of drainage for large storm events, including protection for SuDS systems

mailto:[email protected]



J. Preferred point of connection.

K. Proposed method of flow control

L. Reason for changes to any previously submitted drainage scheme

4. A Method Statement detailing how surface water arising during construction will be handled.

5. Confirmation of land ownership of all land required for drainage and relevant permissions.

6. A SuDS Management Plan, which provides:

A. Details of which body will be responsible for vesting and maintenance for individual aspects of the drainage proposals

B. A management statement to outline the management goals for the site and required maintenance

C. Description of maintenance schedule

D. A site plan including access points, easements and outfalls.

7. Foul drainage proposals

8. Where required for major developments or phasing of minor developments a plan showing each

development plot (e.g. a development block of houses) which shows the allocation of volume storage and discharge rate given to that plot as part of a wider SuDS strategy.

For further advice about the information requested in this checklist please contact the LLFA, Essex County Council, using the following email address [email protected].

A.5 Emergency Planning

Thurrock Council Emergency Planning Team prepares contingency plans for incidents and risks

across Thurrock to ensure adequate preparation and response during flood events. There are also

several groups which support emergency planning across Essex. Where a new development or

change of land use is proposed, flood evacuation plans should be developed through liaison with the emergency planners and the emergency services.

Additionally, following production of this SFRA, it is recommended that emergency planning strategies

should be reviewed to determine the suitability of refuge centres and evacuation routes based on the updated flood risk mapping produced.

Emergency Planning can be broadly split into three phases, all of which should be considered in managing flood risk across the Borough:

1. Before a flood – raising flood awareness, ensuring no inappropriate use of the floodplain/flow

paths, preparing suitable flood emergency plans and communicating them to the wider community;

2. During a flood – Flood alerts and communication, rescuing occupants, providing safe refuge and alternative accommodation;

3. After the flood – providing support to help people recover and return to their homes and businesses.

Consideration of emergency planning is even more critical when it relates to vulnerable sites and essential infrastructure, as further described below.



Vulnerable Sites

Emergency service authorities responsible for hospitals, ambulance, fire and police stations as well as

prisons should ensure that emergency plans, in particular for facilities in flood risk areas, are in place

and regularly reviewed so that they can cope in the event of a major flood. These plans should put in place cover arrangements through other suitable facilities, if deemed needed.

The NPPF classifies police stations, ambulance stations, fire stations and command centres as Highly

Vulnerable buildings. It is essential that all establishments related to these services are located in the

lowest flood risk zones to ensure that in the event of an emergency those services vital to the rescue

operation are not impacted by flood water. Furthermore, development management policies should

seek to locate more vulnerable uses such as schools and care homes in areas at the lowest risk of flooding to minimise the impact of a flood on their vulnerable users.

Allied to this, nominated rest and reception centres should also be identified within the study area and

compared with the outputs of this SFRA to ensure that these centres are not at risk of flooding, so that

evacuees will be safe during a flood event. Developments that would be suitable for such uses would include leisure centres, churches, schools and community centres.

On occasions where development of vulnerable sites within flood risk areas is unavoidable, necessary measures should be implemented to ensure the site is as safe as possible.

Critical Infrastructure

In the event of a flood incident, it is essential that the evacuation and rescue routes to and from any

proposed development remain safe. Floodplain management and emergency response activities must

have a focus on key infrastructure and any properties that are below sea level. Essential infrastructure

located in Flood Zone 3a or 3b must be operational during a flood event to assist in the emergency evacuation process.

Relevant transport authorities and operators should examine and regularly review their infrastructure

including their networks, stations, and depots, for potential flooding locations and to identify the need

for any flood risk reduction measures. For large stations and depots, solutions should be sought to store or disperse rainwater from heavy storms in a sustainable manner.

Emergency Planning Teams

Thurrock Council Emergency Planning Team prepares contingency plans for incidents and risks

across Thurrock. There are also several groups which support emergency planning across Essex, these are listed below:

1. Crisis Support Team for Essex

2. Essex Resilience Forum

3. Community Risk Register

A.6 Water Environment

A key objective of the WFD is the requirement to prevent deterioration in the current status of water

bodies, whilst Heavily Modified Water Bodies (HMWBs) must achieve good ecological potential within

a set deadline. If an activity has the potential to impact on the ecology or morphology of a water body, the risk of causing deterioration in the status must be assessed.

Thurrock is covered by the Thames River Basin Management Plan (RBMP), which identifies the

current quality of water bodies in the Borough and sets objectives for making further improvements to the ecological and chemical quality.

Within Thurrock Council, the Mardyke is generally not designated as a Heavily Modified Water Body

(HMWB) and has an overall status of moderate under the WFD. However, the Mardyke (West

Tributary) and Mardyke (East Tributary) have a poor overall status and poor ecological status,

although it is not designated as a HMWB. The Mardyke and Fobbing water body is designated as a HMWB and has moderate ecological potential under the WFD.

http://www.crisissupportessex.org/index.html

http://www.essexprepared.co.uk/



The section of Thames south of Thurrock extending east to Stanford-le-Hope is classed as the

‘Thames Middle’ water body, and is designated as a HMWB, with a current overall potential of

moderate. The Thames Lower water body runs east from Stanford-le-Hope and is also designated as a HWMB, with an ecological and overall status of moderate.

Actions identified in the LFRM Flood Strategy have the potential to balance social, economic and

environmental aims and objectives to achieve wider environment benefits. The implementation of

sustainable flood risk management options and measures provides a good opportunity to improve the

environment across Thurrock. The Local Flood Risk Management Flood Strategy will contribute to the achievement of wider environmental objectives through the following actions:

a. As flood risk management projects, schemes and initiatives identified within the

Programme and Strategic Investment Plan are developed, Thurrock Council will

ensure compliance with wider environmental objectives and targets (e.g. those set

out by WFD and the RBMP) by ensuring water bodies and protected areas are

suitably protected and that the implementation of any scheme does not cause any deterioration of waterbodies.

b. Enhancement of biodiversity and habitat creation within any future capital schemes.

c. Improvement of water quality through use of source control measures such as SuDS.

d. Working with key partners to ensure sustainable land use planning and safeguarding green open spaces to help reduce flood risk.

It is anticipated that growing population numbers and changing climate patterns will place increased

pressure on water resources across the Thames Basin. New development can assist in alleviating this

water scarcity by incorporating water efficiency measures such as grey water recycling, rainwater

harvesting and water use minimisation technologies. This will also have a substantial benefit on the

sewer system which will receive less wastewater from properties, potentially freeing up capacity during flood events.

Consultation and Coordination

For future flood risk management within the Borough to be successful, it is essential that relevant

partners and stakeholders, who have responsibility for flood risk management assets, work collaboratively to reduce flood risk.

In particular, Thurrock Council should continue to work with the Environment Agency and others to

ensure ongoing maintenance and improvement of the River Thames Defences. This will include

ensuring that the recommendations of the TE2100 Plan are implemented in new and existing

developments, to keep communities safe from flooding in a changing climate and improving the local environment.

Opportunities should be sought to reduce the risk of flooding from surface water and sewer surcharge

through consultation with Anglian Water, to determine key areas for maintenance and locations that would benefit from flood alleviation schemes.

It is further recommended that Thurrock Council continues to collaborate with stakeholders to

maintain and expand upon the existing understanding of flood risk across the Borough and, in

particular, to confirm the impact of revised climate change allowances on understanding of fluvial flood risk.



Appendix B Mapping

Map Number Map Title

Map 001 River Network

Map 002 Topography

Map 003 Superficial Geology

Map 004 Bedrock Geology

Map 005 Historic Fluvial Flood Map

Map 006 Records of Sewer Flooding

Map 007 Risk of Flooding from Rivers and Sea

Map 008 Risk of Surface Water Flooding

Map 009 Susceptibility to Groundwater Flooding

Map 010 Risk of Flooding from Reservoirs

Map 011 Infiltration SuDS Suitability

Map 012 Environment Agency Flood Warning Areas



Appendix C Breach Modelling Flood Depth Mapping



Appendix D Breach Modelling Flood Hazard Mapping



Appendix E Breach Modelling Time to Inundation Mapping



Appendix F Techniques for SuDS in Thurrock



Appendix G Guidance for Thames Area Climate Change

Allowances



Appendix H Climate Change Analysis for River Mardyke



Appendix I FRA Checklist

What to Include in the FRA Source(s) of Information

1.Site Description

Site address - -

Site description - -

Location plan Including geographical features, street names, catchment areas,

watercourses and other bodies of water

SFRA Appendix B

Site plan Plan of site showing development proposals and any structures which

may influence local hydraulics e.g. bridges, pipes/ducts crossing

watercourses, culverts, screens, embankments, walls, outfalls and

condition of channel

OS Mapping

Site Survey

Topography Include general description of the topography local to the site. Where

necessary, site survey may be required to confirm site levels (in

relation to Ordnance datum).

Plans showing existing and proposed levels.

SFRA Appendix B,

Site Survey

Geology General description of geology local to the site. SFRA Appendix B

Ground Investigation Report

Watercourses Identify Main Rivers and Ordinary Watercourses local to the site. SFRA Appendix B

Status Is the development in accordance with the Council’s Spatial Strategy? Seek advice from Thurrock

Council if necessary

2. Assessing Flood Risk

The level of assessment will depend on the degree of flood risk and the scale, nature and location of the proposed

development. Refer to Table 5-1 regarding the levels of assessment. Not all of the prompts listed below will be relevant for

every application.

Flooding from Rivers Provide a plan of the site and Flood Zones.

Identify any historic flooding that has affected the site, including

dates and depths where possible.

How is the site likely to be affected by climate change?

Determine flood levels on the site for the 1% annual probability (1 in

100 chance each year) flood event including an allowance for

climate change.

Determine flood hazard on the site (in terms of flood depth and

velocity).

Determine the flood level, depth, velocity, hazard, rate of onset of

flooding on the site.

SFRA Appendix B

Environment Agency Flood Map

for Planning (Rivers and Sea).

Environment Agency Products

1-7.

New hydraulic model (where

Environment Agency data not

available)

Flooding from Land Identify any historic flooding that has affected the site.

Review the local topography and conduce a site walkover to

determine low points at risk of surface water flooding.

Review the Risk of Flooding from Surface Water mapping & SWMP

report.

SFRA Appendix B

Topographic survey.

Site walkover.

Risk of Flooding from Surface

Water mapping (EA website).

Flooding from

Groundwater

Desk based assessment based on high level BGS mapping in the

SFRA.

Ground survey investigations.

Identify any historic flooding that has affected the site.

SFRA Appendix B

Ground Investigation Report




Flooding from Sewers Identify any historic flooding that has affected the site.

SFRA Appendix B.

Where appropriate an asset

location survey can be provided

by Anglian Water

http://www.anglianwater.co.uk/d

evelopers/locateasset.aspx

Reservoirs, Docks and

other artificial sources

Identify any historic flooding that has affected the site.

Review the Risk of Flooding from Reservoirs mapping and

Environment Agency breach modelling for the Docks

Risk of Flooding from

Reservoirs mapping

(Environment Agency website).

Updated Thames Breach

Modelling data

3. Proposed Development

Current use Identify the current use of the site. -

Proposed use Will the proposals increase the number of occupants / site users on

the site such that it may affect the degree of flood risk to these

people?

-

Vulnerability

Classification

Determine the vulnerability classification of the development. Is the

vulnerability classification appropriate within the Flood Zone?

SFRA Table 5-2

SFRA Table 5-3

4. Avoiding Flood Risk

Sequential Test Determine whether the Sequential Test is required.

Consult Thurrock Council to determine if the site has been included

in the Sequential Test.

If required, present the relevant information to Thurrock Council to

enable their determination of the Sequential Test for the site on an

individual basis.

SFRA Section 5

Exception Test Determine whether the Exception Test is necessary.

Where the Exception Test is necessary, present details of:

Part 1) how the proposed development contributes to the

achievement of wider sustainability objectives as set out in the

Thurrock Council Sustainability Appraisal Scoping Report.

(Details of how part 2) can be satisfied are addressed in the

following part 5 ‘Managing and Mitigating Flood Risk’.)

SFRA Section 5

Refer to Thurrock Council

sustainability objectives

5. Managing and Mitigating Flood Risk

Section 6 of the SFRA presents measures to manage and mitigate flood risk and when they should be implemented. Where

appropriate, the following should be demonstrated within the FRA to address the following questions:

How will the site/building be protected from flooding, including the potential impacts of climate change, over the development’s

lifetime?

How will you ensure that the proposed development and the measures to protect your site from flooding will not increase flood

risk elsewhere?

Are there any opportunities offered by the development to reduce flood risk elsewhere?

What flood-related risks will remain after you have implemented the measures to protect the site from flooding (i.e. residual

risk) and how and by whom will these be managed over the lifetime of the development (e.g. flood warning and evacuation

procedures)?

Development Layout

and Sequential

Approach

Plan showing how sensitive land uses have been placed in areas

within the site that are at least risk of flooding.

SFRA Section 5.2




Finished Floor Levels Plans showing finished floor levels in the proposed development in

relation to Ordnance Datum taking account of indicated flood

depths.

SFRA Section 5.3

Flood Resistance Details of flood resistance measures that have been incorporated

into the design. Include design drawings where appropriate.

Flood Resilience Details of flood resilience measures that have been incorporated

into the design. Include design drawings where appropriate.

Safe Access / Egress Provide a figure showing proposed safe route of escape away from

the site and/or details of safe refuge. Include details of signage that

will be included on site.

Where necessary this will involve mapping of flood hazard

associated with river flooding. This may be available from

Environment Agency modelling, or may need to be prepared as part

of hydraulic modelling specific for the proposed development site.

SFRA Section 5.4

Flow Routing Provide evidence that proposed development will not impact flood

flows to the extent that the risk to surrounding areas is increased.

Where necessary this may require modelling.

Riverside

Development Buffer

Zone

Provide plans showing how a buffer zone of relevant width will be

retained adjacent to any Main River or Ordinary Watercourse in

accordance with requirements of the Environment Agency and

Thurrock Council

Surface Water

Management

Details of the following within FRA for all other developments

located within Flood Zones 2 and 3:

Calculations (and plans) showing areas of the site that are

permeable and impermeable pre and post-development.

Calculations of pre and post-development runoff rates and volumes

including consideration of climate change over the lifetime of the

development.

Details of the methods that will be used to manage surface water

(e.g. permeable paving, swales, wetlands, rainwater harvesting).

Where appropriate, reference the supporting Outline or Detailed

Drainage Strategy for the site.

Information on proposed management arrangements

SFRA Appendix B

Flood Warning and

Evacuation Plan

Where appropriate reference the Flood Warning and Evacuation

Plan or Personal Flood Plan that has been prepared for the

proposed development (or will be prepared by site owners).



Appendix J Thurrock SFRA Hydraulic Breach Modelling

Methodology



Appendix K Maintaining the SFRA



Maintaining the SFRA &

AECOM Infrastructure & Environment UK Limited

Midpoint

Alencon Link

Basingstoke

Hampshire RG21 7PP

UK

T: +44(0)1256 310200

aecom.com

Thurrock Council - Level 1 Strategic Flood Risk Assessment ...

Documents

Transcript of Thurrock Council - Level 1 Strategic Flood Risk Assessment ...