Rye Stage 1 Surface Water Management Plan

Final Report

June 2015

East Sussex County Council

County Hall

St Anne's Crescent

LEWES

East Sussex

BN7 1UE

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JBA Project Manager Jennifer Hill 35 Perrymount Road Haywards Heath West Sussex RH16 3BW

Revision History

Revision Ref / Date Issued Amendments Issued to

Draft Report v1 / May 2015 N/A Tom Schindl (East Sussex County Council)

Final Report v2 / June 2015 Address comments from the steering group

Tom Schindl (East Sussex County Council)

Final Report v3 / July 2015 Address comments from Rother District Council

Nick Claxton (East Sussex County Council)

Contract This report describes work commissioned by Tom Schindl, on behalf of East Sussex County Council, by an email dated 06/08/2014. East Sussex’s representative for the contract was Tom Schindl. Jenny Hill and Robert Waygood of JBA Consulting carried out this work.

Prepared by .................................................. Jennifer Hill BSc MSc

Analyst

Reviewed by ................................................. Rachel Huitson MSc CEnv MCIWEM C.WEM

Director

Purpose This document has been prepared as a Final Report for East Sussex County Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared.

JBA Consulting has no liability regarding the use of this report except to East Sussex County Council.

Acknowledgements JBA would like to acknowledge and thank Rother District Council, Romney Marshes Internal Drainage Board, Southern Water, the Environment Agency, East Sussex County Council and REACT for all their assistance during this project.

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Executive Summary A Surface Water Management Plan (SWMP) is a study to understand the flood risk that arises from local flooding, which is defined by the Flood and Water Management Act 2010 as flooding from surface runoff, groundwater, and ordinary watercourses.

SWMPs are led by a partnership of flood risk management authorities who have responsibilities for aspects of local flooding, including the County Council, Local Authority, the Environment Agency, Sewerage Undertaker, Internal Drainage Boards and other relevant authorities.

East Sussex County Council as Lead Local Flood Authority (LLFA) has led the production of the Rye Stage 1 SWMP in partnership with Rother District Council, the Environment Agency, Southern Water, Romney Marshes Area IDB and REACT. This steering group was established as part of the SWMP process. It is proposed that the monitoring and reporting of the implementation of the action will be undertaken locally and it is expected that partners will take forward actions independently, and convene as and when appropriate.

Rye is a town in the Rother district in East Sussex. Expansion of the town is constrained by the Walland Marshes to the east and the High Weald Area of Outstanding Natural Beauty to the west. As a result, growth of the town has been restricted and the population has remained around 4,500 for the last 60 years.

Relatively impermeable geological formations coupled with a high soil saturation creates conditions for high surface water flood risk in Rye.

To better understand flood risk in Rye the SWMP has strived to collate all the available incident records of flooding along with any modelling of flood risk. This data has been supplied by the project partners.

In attempting to understand the flood risk, a Source-Pathway-Receptor model was applied. The application of such a model facilitates flood risk mitigation by potentially addressing the source (often very difficult), blocking or altering the pathway and even removing the receptor e.g. navigate development away.

Priority areas have been identified where there are repeated flood incidents and/or multiple flood mechanisms along with areas of predicted flood risk. The priority areas identified are:

The Strand;

The Tilling Green Estate, which includes the sub area of Tilling Green School;

North Salts; and

The Grove.

The flood history and risk data has been used to draw up three action plans to manage the local flood risk. Each of these action plans operate at a different scale, with the generic action plan relevant to all of Rye the priority area action plan relevant to the identified priority areas and the incident specific action plan relating to individual flood incidents reported.

Prioritised actions in Rye include

commissioning a study to understand the flood mechanisms operating at the Strand;

targeting highway gully maintenance on North Salts; and

undertaking investigation works to understand the culvert condition under The Old Brickyard.

There is the potential for future developments to be at risk of flooding and/or exacerbate the existing problem. Consequently, it is recommended that Rother District Council incorporate the SWMP findings into its development plans.

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List of Figures Figure 1-1: A map to identify the location of all the watercourses in Rye ................................ 8

Figure 1-2: Conceptualisation of the integration of flooding mechanisms. ............................... 9

Figure 1-3: A map of Rye, the underlying geology ................................................................... 10

Figure 3-1: Flood history in Rye................................................................................................ 16

Figure 3-2: Main River flood risk ............................................................................................... 17

Figure 3-3: uFMfSW in Rye ...................................................................................................... 18

Figure 3-4: Frism output for the number of residential receptors affected by surface water flooding at a 1 in 1000 year return period ................................................................ 19

Figure 3-5: Groundwater flood risk in Rye ................................................................................ 20

Figure 3-6: Priority areas identified in Rye ............................................................................... 21

Figure 3-7: The Grove priority area .......................................................................................... 22

Figure 3-8: Tilling Green Estate priority area ............................................................................ 23

Figure 3-9: RY18 potential development site ........................................................................... 24

Figure 3-10: The Strand priority area ....................................................................................... 25

Figure 3-11: North Salts priority area ....................................................................................... 26

Figure 4-1: Strategic development areas identified in Rye. ...................................................... 27

Figure 5-1: Action plan for The Strand ..................................................................................... 31

Figure 5-2: Action plan for Tilling Green estate ........................................................................ 32

Figure 5-3: Action plan for Tilling Green School development site .......................................... 33

Figure 5-4: Action plan for North Salts ..................................................................................... 33

Figure 5-5: Action Plan for The Grove ...................................................................................... 34

List of Tables Table 2-1: Partners involved in the SWMP process ................................................................. 12

Table 2-2: Catchment data and data supplier .......................................................................... 13

Table 2-3: Flood risk modelling data and supplier .................................................................... 13

Table 2-4: Data quality scoring system .................................................................................... 14

Table 2-5: Received data and allocated quality score .............................................................. 14

Table 3-1: Number of receptors in Rye at risk from surface water flooding ............................. 19

Table 3-2: The Grove Source-Pathway-Receptor model ......................................................... 22

Table 3-3: Source-Pathway-Receptor for Tilling Green Estate ................................................. 23

Table 3-4: Source-Pathway-Receptor for Tilling Green School ............................................... 24

Table 3-5: Source-Pathway-Receptor for the Strand ............................................................... 25

Table 3-6: Source-Pathway-Receptor for North Salts .............................................................. 26

Table 4-1: Strategic development areas allocated in Rye ......................................................... 28

Table 5-1: Action plans ............................................................................................................. 29

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Abbreviations AONB .............................. Area of Outstanding Natural Beauty

AStGWF .......................... Areas Susceptible to Ground Water Flooding

AStSWF .......................... Areas Susceptible to Surface Water Flooding

BGS ................................ British Geological Survey

CAM ................................ Condition Assessment Manual

CFMP .............................. Catchment Flood Management Plan

CIL .................................. Community Infrastructure Levy

DAP ................................. Drainage Area Plan

DRN ................................ Detailed River Network

ESCC .............................. East Sussex County Council

FRA ................................. Flood Risk Assessment

FMfSW ............................ Flood Map for Surface Water

IDB .................................. Internal Drainage Board

LLFA ............................... Lead Local Flood Authority

LFRMS ............................ Local Flood Risk Management Strategy

NPPF .............................. National Planning Policy Framework

NRD ................................ National Receptors Database

RFCC .............................. Regional Flood and Coastal Communities

RMA ................................ Risk Management Authority

SAB ................................. SuDS Approving Body

SAC……………………….Special Areas of Conservation

SFRA .............................. Strategic Flood Risk Assessment

SHLAA……………………Strategic Housing Land Availability Assessment

SPA……………………….Special Protection Areas

SSSI……………………....Sites of Special Scientific Interest

SuDS ............................... Sustainable Drainage Systems

SWMP ............................. Surface Water Management Plan

uFMfSW .......................... updated Flood Map for Surface Water

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Executive Summary ................................................................................................................. 2

List of Figures .......................................................................................................................... 3

List of Tables ............................................................................................................................ 3

Abbreviations ........................................................................................................................... 4

1 Introduction ................................................................................................................. 6

1.1 What is a surface water management plan .................................................................. 6 1.2 Summary of aim and objectives ................................................................................... 6 1.3 Stages of SWMP development ..................................................................................... 7 1.4 Sources of flood risk ..................................................................................................... 7 1.5 Study area .................................................................................................................... 9

2 Preparation .................................................................................................................. 12

2.1 Partnership approach ................................................................................................... 12 2.2 Data collation and review.............................................................................................. 12

3 Strategic assessment ................................................................................................. 15

3.1 Flood history ................................................................................................................. 15 3.2 Flood risk ...................................................................................................................... 16 3.3 Priority areas ................................................................................................................. 20

4 Planning ....................................................................................................................... 27

4.1 Local Development Framework .................................................................................... 27 4.2 Development areas in priority areas ............................................................................. 28

5 SWMP action plan ....................................................................................................... 29

5.1 Monitoring the action plan............................................................................................. 29 5.2 Communicating the action plan .................................................................................... 29 5.3 Generic action plan ....................................................................................................... 29 5.4 Priority areas ................................................................................................................. 31 5.5 Incident specific actions ................................................................................................ 34 5.6 Way forward .................................................................................................................. 35

Appendices............................................................................................................................... 36

A Appendix - Data Quality Score .................................................................................. 36

B Appendix – Flood History Table ................................................................................ 36

C Appendix – Quantifying Surface Water Flood Risk ................................................ 37

D Appendix – Using the GeoPDF .................................................................................. 38

E Appendix - Incident specific action plan .................................................................. 40

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1 Introduction

1.1 What is a surface water management plan

A Surface Water Management Plan (SWMP) is a study to understand the flood risk that arises from local flooding, which is defined by the Flood and Water Management Act 2010 as flooding from surface runoff, groundwater, and ordinary watercourses.

SWMPs are led by a partnership of flood risk management authorities who have responsibilities for aspects of local flooding, including the County Council, District Council, Sewerage Undertaker, Internal Drainage Boards and other relevant authorities.

Rye has been identified as an area potentially at risk of local flooding in the East Sussex Local Flood Risk Management Strategy (LFRMS).

The purpose of a SWMP is to identify what the local flood risk issues are, what options there may be to prevent them or the damage they cause and who should take these options forward. This is presented in an action plan which lists the partners who are responsible for taking the various options forward. The action plan, which will be reviewed periodically, is agreed by all project partners to tackle the flood risks that are identified.

This SWMP was commissioned by East Sussex County Council (ESCC) to investigate the local flood risks across the urban centre of Rye as part of its remit for strategic oversight of local flood risk management in East Sussex, under the Flood and Water Management Act 2010.

1.2 Summary of aim and objectives

The aims and objectives of the Rye Stage 1 SWMP are as follows:

1. Establishment of a local partnership

2. The consolidation of a comprehensive flood history for all relevant local flood risk sources

3. The identification, collation and mapping of all available flood data and its availability for future use, including an assessment of the reliability of the data

4. The identification, where possible from the available data, of flood-prone areas

5. The identification of areas where existing data may be missing, compromised or unreliable as a consequence of inappropriate local assumptions, additional local features (such as flood barriers) or for any other reason together with options to improve confidence in the overall outcome

6. The identification of areas where flood risk originates from a combination of sources (for example from rivers and highway run-off)

7. Identification of any proposed or allocated developments within the study area together with the likely impact on flood risk that they may have

8. The preparation of source pathway receptor models for all known incidents, risks, sources and flood-prone areas that have been identified

9. Where appropriate, the identification of any “easy win” opportunities that may become apparent without further detailed risk assessment

10. To provide the relevant local planning authorities with data in a form to support the review of strategic flood risk assessments

11. To provide a clear plan for further work that may be considered necessary to manage or improve clarity of the flood risks identified in the report. These should include, but are not limited to, ownership of the actions required for risk mitigation, a timescale for these actions together with indicative capital costs

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1.3 Stages of SWMP development

The SWMP has been prepared across a series of three phases, as follows:

Preparation: Building a partnership approach to local flood risk management through integrated working between the risk management authorities (RMAs). Gathering evidence of and information about flooding

Risk Assessment: An initial assessment to determine the highest risk locations and the key issues upon which the action plan should focus. We will be using publicly available datasets in combination with local records of flooding to inform this assessment

Action Plan: Preparation of an action plan that recommends a range of actions for the reduction of flood risk across the SWMP area. The action plan will:

o outline the actions required and where and how they should be undertaken;

o set out which partner(s) or stakeholder(s) is/are responsible for implementing the actions and who will support them; and

o identify priorities.

1.4 Sources of flood risk

One of the purposes of a SWMP is to identify what the local flood risk issues are, and to summarise the flood history and predicted flood risk to the area. Flood risk can arise from a number of sources, as listed within this section.

1.4.1 Watercourses

Main river

A main river is any watercourse which is designated as such on the Environment Agency's main river map, and for which the Environment Agency has responsibilities and powers. Main rivers are generally the larger arterial watercourses but smaller watercourses can be designated if they pose a significant flood risk. Where fluvial or tidal flooding from main rivers is the sole source of flooding, it is the responsibility of the Environment Agency. Actions to mitigate fluvial flooding from main river are outside the scope of a SWMP, and are addressed in a Catchment Flood Management Plan, or other local more detailed studies. However, consideration of main river flooding should be made in SWMPs to examine how fluvial flooding interacts with other, local flood sources.

Rye is situated two miles from the sea, at the confluence of the three main rivers: Tillingham, Brede and Rother. The three main rivers at Rye have are tidally influenced. Naturally, each of these watercourses would receive tidal ingress at Rye. However, a sluice on the River Brede prevents tidal ingress upstream of Harbour Road and a sluice on the River Tillingham prevents tidal ingress upstream of Winchelsea Road. The tidal Brede benefits from flood defences.

Ordinary watercourse

An ordinary watercourse is a statutory type of watercourse in England and Wales. They include rivers, streams, ditches and drains which do not form part of a main river. ESCC and Romney Marshes Area Internal Drainage Board1 has permissive powers to carry out works on ordinary watercourses and also has responsibilities in relation to consenting and enforcement.

In Rye there is a network of ordinary watercourses which drain to the aforementioned main rivers. These include the Rye harbour sewer and Northpoint sewer referenced in Figure 1-1. Many of the ordinary watercourses within the Rye study boundary are maintained by the Romney Marshes Area IDB.

1 An Internal Drainage Board’s permissive power pertain to those ordinary watercourses within their boundaries

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Figure 1-1: A map to identify the location of all the watercourses in Rye

1.4.2 Sewers

Sewers describe the below ground infrastructure for the conveyance of waste water. They are categorised by the type of waste water they remove. The categories include:

Foul sewer

Surface Water sewer

Combined sewer

Foul sewers convey wastewater. Public surface water sewers take runoff from domestic

premises, yards and roofs, also under agreement highway drainage and combined sewers convey a mix of both foul water and surface water.

Southern Water is responsible for the public sewer networks in this area. As a partner in the SWMP process, Southern Water has provided records of their assets in Rye. The town is served by Rye wastewater water treatment works (WTW) situated between Rye and Rye Harbour. The historic town centre is served by a combined network whereas the newer developments to the north of the railway line have largely separate sewerage systems, with a foul network to convey trade and household wastewater and a surface water sewer system to convey runoff.

For the purpose of this study, the surface water sewer network is the main emphasis. The performance of this drainage network relates directly to the proportion of rainfall which forms pluvial runoff and the inflow to ordinary watercourses from drainage networks discharging.

Sewer flooding from the foul water network is the responsibility of Southern Water. However, foul water flooding due to hydraulic overload has been considered in the SWMP to examine interactions between foul sewer surcharge and other, local flood sources. A storm response on a foul water sewer network is often caused by flooding of manholes or misconnections from the surface water network. Therefore, by addressing the surface water issues in the catchment this, in some cases, can help relieve problems on the foul water network. In some cases, Southern Water asset maps show a foul system when it was actually originally designed as combined. Further investigation could identify these areas and the asset map should be updated accordingly.

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It should be noted that a spill of wastewater sewage presents a potential local water quality issue. Despite water quality not being the principal driver for this project, a SWMP could provide a framework for improving the quality of water. Actions resulting from this SWMP such as SuDS could result in an improvement in water quality.

1.4.3 Surface water

Surface water flooding occurs when rainfall fails to infiltrate to the ground or enter the drainage system. Ponding generally occurs at low points in the topography. The likelihood of flooding is dependent on not only the rate of runoff but also the groundwater level and the condition of the surface water drainage system (i.e. surface water sewers, ESCC highway authority drains and gullies, open channels, ordinary watercourses and SuDS).

1.4.4 Integrated flood risk

In an urban environment such as Rye, flooding mechanisms are often closely integrated. The flood mechanisms that operate in Rye and how they interact has been conceptualised in Figure 1-2.

Figure 1-2: Conceptualisation of the integration of flooding mechanisms.

1.5 Study area

Rye is a historic market town in the eastern half of the Rother district. It is the main service and employment centre in the area2. Expansion of the town is limited by the High Weald Area of Outstanding Natural Beauty (AONB) to the west which contains several Sites of Special Scientific Interest (SSSI), Special Areas of Conservation (SACs), Special Protection Areas (SPAs), and Sites of Nature Conservation Importance, and the Walland Marsh to the east. As a result, growth around the periphery of Rye has been limited and the population has remained relatively static over the last 60 years. The development which has occurred has predominately been infill on available land.

The underlying bedrock geology of the area is the Wealden Group; the Wealden Group comprises of interbedded sandstones, siltstones, mudstones, clay and limestones. A large proportion of the study area’s bedrock geology however is overlain by superficial deposits. Superficial deposits include; alluvium and undifferentiated raised marine deposits at Rye Harbour. This geology has mixed permeability properties and surface runoff rates are likely to vary depending on localised soils and geology. Due to the alluvium deposits, it is likely that the initial soil moisture content will have a significant impact on runoff during a rainfall event. A map of the study area, describing the geology and area covered is shown in Figure 1-3.

2 Rother District Council (2014) Rother Local Plan: Core Strategy

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Figure 1-3: A map of Rye, the underlying geology

Currently, no hydrological analysis or hydraulic modelling has been undertaken for any of the ordinary watercourses in Rye.

1.5.1 National mapping

The Environment Agency has undertaken a number of national scale modelling and mapping projects to understand relative flood risk across England and Wales.

Fluvial

The flood map of fluvial flood risk in England and Wales was originally created on a national scale for all the main rivers. The mapping is continually updated as more detailed, local flood mapping studies are undertaken by the Environment Agency. As discussed in section 1.4.1, flooding from fluvial (main river) sources alone is not within the scope of a SWMP, but this mapping can be useful to examine integration between fluvial flooding and flooding from local sources. As there are three main rivers in Rye, the fluvial flood maps are applicable to this SWMP.

Surface water

The sources of information available from the Environment Agency relating to the identification of potential surface water flood risk in Rye are the:

Areas Susceptible to Surface Water Flooding (AStSWF) - Since July 2009, these maps have been available to Local Resilience Forums and Local Planning Authorities, and provided a starting point in understanding the broad areas where surface water flooding is likely to cause problems.

Flood Maps for Surface Water (FMfSW) - these followed on from the AStSWF maps and provide a more realistic representation than the AStSWF maps in many circumstances.

Updated Flood Maps for Surface Water (uFMfSW) – The Environment Agency have produced an updated version of the previous Flood Maps for Surface Water (FMfSW) dataset. The uFMfSW is the result of a more refined modelling methodology which aims

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to provide a more accurate representation of surface water flood risk across England and Wales.

As the updated Flood Map for Surface Water is the most up to date and detailed dataset available, this will form the basis of our surface water flood risk assessment.

Groundwater

Two sources of data were provided by ESCC relating to the identification of potential groundwater flood risk in Rye. This included data from Areas Susceptible to Ground Water Flooding (AStGWF) and ESI Groundwater Flood Risk Map.

AStGWF are identified in a 1 kilometre square grid of England and Wales. It shows the proportion of each grid square where the geological and hydrogeological conditions show that groundwater might emerge3.

The ESI Groundwater Flood Risk Map provides classification of groundwater flooding risk in four categories in a 50 metre grid of England and Wales. The risk classifications of negligible, low, moderate and high represent the likelihood and severity of flooding resulting from extreme groundwater levels within an estimated 1 in 200 year return period.

The ESI Groundwater Flood Risk Map has been used in this SWMP as it the most detailed dataset available.

3 Environment Agency (2012) Areas Susceptible to Ground Water Flooding - available at

http://www.geostore.com/environment-agency/WebStore?xml=environment-agency/xml/dataLayers_ASGWF.xml

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2 Preparation

2.1 Partnership approach

Within Rye, flood risk is managed by multiple agencies, including the County Council, the District Council, the Environment Agency and Southern Water. Often, urban flooding is caused by multiple mechanisms, which fall under the jurisdiction of different agencies. Therefore, a holistic approach is required to solve a flooding issue. As such partnership working is a key emphasis in East Sussex's SWMP process.

To fully understand flood risk in Rye the SWMP has strived to collate all the available records of flood history and modelling of flood risk. This data has been collected from the project partners. Using this data, an action plan has been drawn up which attributes specific project partners as owners of the action. Again, the importance of partner engagement is crucial here so that agreed actions are followed through to completion.

The partnership approach also enables effective resource allocation and efficiencies to be achieved by sharing common duties between co-operating agencies.

2.1.1 Project partners

For the purpose of this project, partners are defined as organisations with responsibility for the decision that needs to be taken to manage flood risk. The partners involved in the Rye SWMP are listed in Table 2-1.

Organisation Representative(s)

East Sussex County Council Nick Claxton, Tom Schindl and Fiona Hartland

Rother DC Drainage Engineer Alan Dodge

Rother DC Emergency Planner Kevin Wallis

ESCC Highway Authority Nathan Morton-Clarke and Tom Crawshaw

Environment Agency Peter Amies

Southern Water Mike Tomlinson

Romney Mashes IDB Nick Botting

REACT Anthony Kimber

Table 2-1: Partners involved in the SWMP process

The project partners have supplied the data to inform this SWMP and have been attributed as action owners in Section 5; the SWMP action plan. The Rye Emergency Action Community Team (REACT) have been involved throughout the preparation of this SWMP. REACT have supported the production of the SWMP by passing on their detailed local knowledge of flood incidents that have occurred in Rye and explaining the impact of flooding on the community.

In addition to the above, the Rother District Council (RDC) Planning department was also involved in the SWMP. RDC as the local planning authority is not directly responsible for managing flood risk but it does hold information useful to the SWMP. Furthermore, as the authority responsible for setting local planning policy, it sets the development strategy for the area. Development Manager Richard Wilson represented the Rother planning policy team.

2.2 Data collation and review

Collectively, East Sussex County Council and JBA Consulting received data from each key partner in various forms.

The majority of the data was supplied as GIS points with associated attributes. As mapping is an effective method for communicating the risk, it was decided to keep the data in this format and add to the records with new data collected from other sources. The geo-spatial element of the data allowed for sensibility checking; for example, if fluvial flooding points are located near a watercourse.

The quality of this data was summarised according to a scoring system which is based on the scoring from the SWMP technical guidance. A full list of data and its associated score is located in Appendix A. In summary, catchment data has been provided by East Sussex County Council and the Environment Agency. A list of catchment data is displayed in Table 2-2 below.

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East Sussex County Council Environment Agency

Bedrock and superficial deposits geology (under licence from BGS)

National Receptors Database (NRD)

Main river centreline

Gully point locations

Detailed River Network (DRN)

Aquifer designation

Table 2-2: Catchment data and data supplier

Flood risk maps based on national scale modelling have been provided by the Environment Agency. A list of flood risk mapping data sources is shown in Table 2-3.

Environment Agency East Sussex County Council

Areas susceptible to ground water flooding

ESI Groundwater Flood Risk Updated flood map for surface water: 30, 100 and 1000 year return periods

Fluvial flood map: 100 year and 1000 year return period

Table 2-3: Flood risk modelling data and supplier

East Sussex County Council as LLFA maintains a flood incident register outlining the location, date and description of reported flooding across the County. This data was utilised in the preparation of this SWMP. In addition, flood history records were provided to East Sussex County Council by the project partners. Data included, but was not limited to: East Sussex County Council Highways Public Enquiry Manager (PEM) register and Southern Water's Sewer SWMP summary abstract from the Sewer Incident Report Form (SIRF) register.

A list of all the data received during the Rye SWMP is available in Appendix A.

2.2.1 Data quality scoring

Uncertainty can arise throughout any risk assessment and risk management process. Types of uncertainty can include:

Model - models may not be accurate or complete

Environmental - natural variability may not represent conceptual model assumptions

Knowledge – scientific data may be incomplete

Sample - sample measurements may be inaccurate or the validity may be queried

Data - data may be extrapolated or interpolated from other sources

Scenario - scenarios might not fully describe the problem

Understanding the uncertainty is an important part of the SWMP process, as decisions are made based on the findings. It is important that all project partners and stakeholders are clear about what the limitations of the findings are before making decisions on the level of investment (resources and funding) that may be needed in the future.

The SWMP technical guidance emphasises the importance of understanding the quality of the data used to inform an SWMP. The guidance presents a scoring system to rank the data according to its quality. For Rye Stage 1 SWMP, this scoring system has been modified. The modified scoring system (in Table 2-4) was required because the majority of the data received a quality score of 2 and assumptions made with the data scored 3. The result was not being able to distinguish between the value of these data sources. Therefore, a refined scoring system was developed to provide a more informative data score.

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Data Quality Score

Description Sub-category

1 Best possible, no better data available

N/A

2 Data with known deficiencies

2a) the known deficiencies are missing or duplicated data

2b) the known deficiencies are missing and duplicated data

3 Assumption based on available data

3a) Assumptions confirmed with local data

3b) Assumed data confirmed by cross referencing with other records

3c) Assumed data based on a single dataset

4 Educated guess based on experience N/A

Table 2-4: Data quality scoring system

Under this scoring system all supplied data receives a data quality scoring system of 1 or 2. Information that has been assumed from the data received scores of 3 or 4. The sub-categorisation of the data score distinguishes the relative quality of the data.

This confidence scoring system can be applied to the received data, the source-pathway-receptor model and the selected priority areas.

The flood history data used to inform this SWMP has been scored according to the data which was provided, and that which was missing. Table 2-5 lists the data provided to the Rye SWMP and the data quality score associated with it.

Data Data Quality Score

ESCC records of flooding 1

Highways PEM register 2a

Southern Water SIRF 1

Fire and Rescue 2b

Table 2-5: Received data and allocated quality score

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3 Strategic assessment The Stage 1 SWMP for Rye provides a high level assessment of the local flood risk within the study area. This risk assessment details the level of risk across the study area, allowing for the identification of areas most susceptible and vulnerable to flooding. The assessment utilises flood incident records, together with flood risk maps.

3.1 Flood history

Flood incident data provided geographical information on where flooding had been recorded. The data provided by the partners was standardised using the Source-Pathway-Receptor model. A full list of the collated flood history, including a map to illustrate locations is available in Appendix B.

3.1.1 Source-Pathway-Receptor model

The Source-Pathway-Receptor model is a concept that can provide an understanding of all sources of flood hazard. It is particularly useful in this context as it can be used to generalise the data gathered from numerous sources.

Source - the origin of flood water

Pathway - a route or means by which a receptor can be affected by flooding

Receptor - something that can be adversely affected by flooding

Having applied the Source-Pathway-Receptor model it is possible to mitigate the flood risk by addressing the source (often very difficult), block or alter the pathway and even remove the receptor e.g. steer development away.

3.1.2 Applying the Source-Pathway-Receptor model

The information contained within each flood history table varies between sources of data. Data collected by East Sussex County Council and Southern Water contain specifics on the flood source, the pathway and the receptor. In these instances applying the Source-Pathway-Receptor model can be informed completely from recorded data and requires no assumptions.

Data from ESCC Highway Authority PEMs reports always document the receptor and includes a description which often (but not always) explains the flood source and pathway. Whereas data from the emergency services lists the receptor and occasionally the flood source but not the flood pathway. Applying the source-pathway-receptor model to these data requires an element of assumption. Assumptions can be made based on the location of the flood point.

Cross referencing missing data with local, complete data can reduce the uncertainty surrounding assumptions. As a result, the confidence in assumptions can vary.

3.1.3 Historic flood sources

The flood history showed that the most common cause of flooding recorded in Rye was attributed to highway drainage related issues. The location of these incidents are distributed across the town, but there are a number of issues reported in the North Salts area of Rye, to the north east of the study area. It is likely that the infrastructure related to the flooding incidents have subsequently been cleaned or replaced in most cases.

Surface water flooding due to pluvial runoff is the following most common flood source recorded in Rye. Often pluvial flooding is reported in areas where other surface water incidents have also been reported and in areas where flooding from the foul sewerage network has been reported. In extreme rainfall events, drainage infrastructure is likely to be overwhelmed. In these instances pluvial runoff needs to be managed to steer it away from vulnerable receptors.

There are also a number of combined sewer flooding incidents in Rye. The sewer flooding event data provided by Southern Water are attributed specifically to hydraulic overload, where flooding has occurred as a result of insufficient capacity; pipes have a finite capacity and all sewers will likely be overwhelmed depending on the storm return period. Foul water (sewer) flooding as a result of blockage or asset failure are not included as these are considered to be a Southern Water-only issue. Sewer flooding due to hydraulic overload is in response to rainfall. In Rye, there are large areas of combined sewers. These networks can become overwhelmed during heavy rain, producing hydraulic overload and subsequent flooding.

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Many of the outfalls from Southern Water surface water sewers and consented overflows in Rye use flap valves to prevent ingress of fluvial or tidal water into the sewerage system. When flap valves on outfalls are missing or damaged water can enter the system, which can cause overload and flooding. In addition, cracked or otherwise damaged pipework may allow groundwater into the system, where groundwater levels (see section 3.2.5) permit, which can reduce the capacity of the sewerage system. Flood mechanisms are complex and likely integrated, with sewer flooding occurring together with surface water flooding or high groundwater levels.

The final common source of flooding is attributed to “unknown” sources. This is symptomatic of a flood report where no additional information has been recorded. To enhance our understanding of flood risk in Rye, it is recommended that the recording of future flood reports include details of the flood source.

3.1.4 Mapping the flood history

Records of each recorded flood incident are depicted by coloured points in Figure 3-1. The Source-Pathway-Receptor model was applied to each point and the total number of repeated flood incidents was tallied. This enabled the point to be thematically mapped. The colour of the flood point depicts the flood source and asset affected, whereas the size of the flood point depicts the frequency of the flood incidents recorded at that location, from the same source.

Figure 3-1: Flood history in Rye

The recorded incidents of flooding highlights that Winchelsea Road, The Grove, Tilling Green Estate and North Salts to be areas particularly susceptible to flooding. Analysis of the data reveals that flooding infrequently results from a single source. Rather, flooding appears to be the result of a number of sources, which highlights the integrated nature of flooding in Rye.

3.2 Flood risk

The assessment of flood risk utilised the Environment Agency’s existing risk mapping as local flood risk modelling was beyond the scope of this Stage 1 Surface Water Management Plan. The flood risk considered includes flooding from main rivers, surface water and groundwater.

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3.2.1 Main river

Environment Agency, Flood Zone data for Zones 2 and 3 was utilised in the analysis (Figure 3-2).

The main river flood risk in Rye is concentrated along the Rivers Tillingham, Brede and Rother. The tidal flood risk within the study area is significant. However, it should be noted that much of Flood Zone 3 benefits from defences.

Main river flooding from the three tidal rivers running through Rye pose a flood risk to people and property. However, main river risk is outside the scope of a SWMP, and therefore no detailed assessment of this risk has been made. Nevertheless, it is important to consider that fluvial flooding could interact with other, local flood sources at this location.

Figure 3-2: Main River flood risk

3.2.2 Surface water

As there is no local detailed modelling available for Rye, the data used to inform this analysis was the updated Flood Map for Surface Water (Figure 3-3).

The uFMfSW was not designed to assess the risk associated with ordinary watercourses or drainage channels. However by highlighting low points and valleys in the topography some risk from ordinary watercourses is indirectly accounted for.

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Figure 3-3: uFMfSW in Rye

The surface water flood risk in Rye is most noticeable around the Tilling Green Estate, North Salts and The Grove. The number of receptors predicted to be at risk has been calculated in section 3.2.3.

3.2.3 Quantifying surface water flood risk

Using JBA's impact analysis software, Frism (Flood Risk Metrics), we have quantified the predicted surface water flood risk to property in Rye. The analysis has been based on the updated Flood Map for Surface Water (uFMfSW) which is national scale mapping. The analysis includes all the available return periods which are 1 in 30 year, 1 in 100 year and 1 in 1000 year. This analysis follows the methodology used for the Extended Flood Risk Pack for East Sussex County Council, which JBA completed in 2012.

3.2.4 Quantifying surface water flood risk in Rye

The analysis covers all of the study area, split into a 250 metre grid. The receptors were extracted from the National Receptor Database (NRD). Table 3-4 displays the receptor count at risk from surface water in Rye as a whole. The receptors have been divided into dwellings, critical infrastructure and emergency responders. In this instance, critical infrastructure receptors include but are not limited to; educational institutions, care homes and vital services such as electricity sub-stations and water treatment works whereas emergency responders include ambulance stations, fire stations and police stations. For the full list see Appendix C.

Table 3-1 displays the receptor count at risk from surface water in the town of Rye as a whole.

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Return Period Critical Infrastructure

(NRD)

Dwellings (NRD)

Emergency responders

(NRD)

Total

30 1 3 0 4

100 1 8 0 9

1000 2 28 0 30

Table 3-1: Number of receptors in Rye at risk from surface water flooding Analysis indicates the majority of the risk is to residential dwellings with 28 homes predicted to flood during a 1000 year event. All of these dwellings are classified as ground floor properties, but there is no information available on the threshold of the building. There is at least 1 critical infrastructure receptor predicted to flood at all return periods and this rises to 2 in a 1000 year return period event. However, no emergency responders are predicted to flood during any of the return periods examined.

Whilst the assessment appears to indicate that surface water flood risk to properties is low across Rye, records and on site investigations highlight major flooding concerns. These concerns are explored further in subsequent sections of the report.

Figure 3-4 shows the surface water flood risk to dwellings in a 1 in 1000 year return period event. In this figure, purple and dark blue colours represent a greater concentration of receptors predicted to be at risk.

Figure 3-4: Frism output for the number of residential receptors affected by surface water

flooding at a 1 in 1000 year return period

Figure 3- 4 highlights three distinct areas where surface water flood risk affects properties within the 250 metre cells. According to this analysis the areas with greatest surface water flood risk to properties are Winchelsea Road, Rye Harbour, Tilling Green Estate and North Salts. The greatest concentration of risk is at North Salts where there are 12 residential receptors at risk in a 1 in 1000 year return period event.

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The designation of the flooding priority areas have been informed in part by the outcome of this assessment.

3.2.5 Groundwater

Figure 3-5 indicates that most of Rye is at very limited risk of groundwater flooding. This is due to the bedrock geology having limited potential for storing water. However, there is some potential along the River Rother and Tillingham where the superficial deposits have the potential to store water and the water table is elevated along the corridor of the watercourse.

Figure 3-5: Groundwater flood risk in Rye

3.3 Priority areas

The flood history points have been overlaid with predicted flood risk mapping. Together, the reported flood incidents and predicted flood risks identify flooding clusters where the risk is concentrated. These priority areas are shown in Figure 3-6.

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Figure 3-6: Priority areas identified in Rye

The priority areas often highlight areas where flood mechanisms are integrated. This demonstrates the importance of considering how flood pathways interact. Therefore, considering one flood mechanism in isolation may result in a limited understanding of the interactions of flooding from different sources and pathways.

3.3.1 The Grove priority area

This priority area covers the residential area and Rye Primary School in the north of Rye as shown in Figure 3-7.

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Figure 3-7: The Grove priority area

At The Grove, highway flooding has been reported from surface water and sewers. In addition, the school and sport centre car parks have flooded from surface water. The Source-Pathway-Receptor model for The Grove is shown in Table 3-2.

Source Sewers and surface water

Pathway Sewer exceedance and pluvial ponding due to limited drainage

Receptor Highway, public car parks

Table 3-2: The Grove Source-Pathway-Receptor model

A watercourse runs east to west across the priority area draining into the River Tillingham either under gravity or via a pump owned by Rye Primary School. Onsite inspection identified that the watercourse is heavily vegetated and sedimented in places, specifically outside of the Scout hut. Flow into this watercourse is thought to be throttled by a highway culvert under The Grove. Blockage on this culvert is reported to have caused flooding in the upstream field, which is acting as a flood storage area. Any future development in this area should consider improving the sites’ drainage network. Future plans for the school site includes buying additional land and re-landscaping; this provides a significant opportunity for optimising the drainage arrangement.

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3.3.2 Tilling Green Estate priority area

The Tilling Green Estate sits along the banks of the River Tillingham north east of Rye town centre. The estate is built upon reclaimed marsh land and is low lying with a high water table. Natural drainage in the area via infiltration is minimal and surface water ponding is an issue; this is highlighted by the pluvial ponding flooding points shown in Figure 3-8.

Figure 3-8: Tilling Green Estate priority area

The flood risk and flood history show that highways of the Tilling Green estate are susceptible to surface water. The flooding issue at Tilling Green estate has been improved by recent renovation of the Southern Water surface water pumping station on Marley Road. The Source-Pathway-Receptor model for Tilling Green is shown in Table 3-3.

Source Pluvial runoff, foul water and highway drainage

Pathway Predominately pluvial ponding, with some foul exceedance

Receptor Low trafficked roads

Table 3-3: Source-Pathway-Receptor for Tilling Green Estate

Recently, Southern Water has undertaken renovation works to the pumping station, after flooding in this area. Consequently, it is felt that this work has helped managed the flood risk as the January 2015 rainfall event only resulted in minimal flooding.

During a site inspection, subsidence was observed along the highways in the estate. Such subsidence may cause damage to the sewer network in the estate and allow for groundwater ingress. The estate is susceptible to subsidence as result of being built on reclaimed marsh land.

Development site sub-area

The Tilling Green School site (RY18 in Figure 3-9) is now being developed for housing. According to the updated Flood Map for Surface Water there could be an overland flow route south to west which intercepts and ponds at the site.

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Figure 3-9: RY18 potential development site

This site has an existing surface water flood risk and there is a potential flood risk from the culverted watercourse under the Old Brickyard. The current receptor is a school field but under current plans this could be developed to 32 properties. The Source-Pathway-Receptor model for this site is shown in Table 3-4.

Source Pluvial runoff and potential exfiltration from culverted watercourse

Pathway Overland flow from the south west and potential through flow from the south

Receptor Currently a school field, proposed 32 dwellings and a community centre

Table 3-4: Source-Pathway-Receptor for Tilling Green School

There is a culverted watercourse which runs along the southern boundary of the site. This watercourse flows east to west and discharges to an open channel at Gibbets Marsh. It is an ordinary watercourse and has not been adopted by the IDB. As such, management of the watercourse is remains with the riparian land owners. This culvert has been locally attributed to a reoccurring flood issue at Tilling Green School. As a result, both the Environment Agency and the IDB have undertaken investigative works to better understand the flood mechanism. The Environment Agency undertook CCTV survey of the culvert. This survey discovered that the downstream section has no flow running through it but the upstream section has been shown to do so. However, the CCTV survey is incomplete due to limited access, so around 30 metres of culvert remains un-surveyed. During this survey, the cause for the loss of flow was not identified. Following this investigation, the IDB undertook dye tracing to attempt to understand where the flow observed at the upstream end of the culvert was routing to. This test was inconclusive as the dyed water could not be located.

It has been speculated that damage to the culvert is allowing exfiltration from the pipe, with the water percolating into the surrounding soils. If exfiltration is occurring it could cause damage to future development in the area. Further CCTV surveying and/or dye tracing should be utilised to ascertain where the culvert contents are going and the location of any possible damage. Development produces the opportunity to create an open bypass channel along the northern side of the current culverted watercourse.

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3.3.3 The Strand priority area

The Strand priority area covers the residential and commercial area in the centre of Rye (see Figure 3-10).

Figure 3-10: The Strand priority area

Winchelsea Road, locally known as The Strand, has experienced frequent and widespread flooding from the combined sewer network. In addition, pluvial ponding from highway runoff exacerbates the flooding issue at this location. Flooding to highways has reached recorded depths of around 30 centimetres. There are residential properties to the north of the Strand that have thresholds below the road level but these residents have protected themselves with sandbags which has thus far prevented flood water from entering properties.

The predominant flooding source in the area is from the combined sewer network; extensive flooding from the combined sewer occurred in January 2015. The Source-Pathway-Receptor for the Strand is shown in Table 3-5.

Source Combined sewerage network

Pathway Sewer exceedance and rainfall runoff

Receptor A-road highway, residential curtilage

Table 3-5: Source-Pathway-Receptor for the Strand

Following this incident, Southern Water undertook investigations into the cause of the flooding. They investigated whether the system was running clear of blockage and if local pumps were operating correctly. The investigation found no defect in the combined sewerage and therefore concluded that the flooding was related to the heavy rainfall flooding the sewerage network.

On site it was identified that flap valves were missing where sewerage outfalls into the tidally influenced section of the River Brede. It was speculated that the surcharge could be as a result of ingress of water at high tide into the sewerage system. However, this is not confirmed.

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3.3.4 North Salts priority area

This priority area covers the residential area of Military Road in the east of Rye shown in the below figure.

Figure 3-11: North Salts priority area

North Salts is a residential area in the east of Rye, off of Military Road which has a considerable number of reported flooding incidents. The source appearing to be attributed to highway drainage during the period of 2011 to 2015. There is also one reported incident of flooding attributed to a drainage ditch issue along Military Road just north east of the North Salts turning. The Source-Pathway-Receptor model for North Salts in shown in Table 3-6.

Source Surface water

Pathway Runoff from Rye Hill and Military Road

Receptor Highway, residential curtilage and residential dwellings

Table 3-6: Source-Pathway-Receptor for North Salts

Rye Hill and Point Hill, to the north, are topographical high points which slope down steeply towards Military Road. It is likely that during pluvial events, runoff from the slopes would pick up sediment. North Salts road slopes away from Military Road and is a likely pathway for surface water flows, as shown by the uFMfSW. The railway embankment to the south of North Salts impounds surface water runoff here leading to ponding. This loss of energy could cause the surface water to deposit its sediment load, leading to blockage in the drainage systems.

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4 Planning The purpose of this section is to examine the risk of flooding (from local sources) to allocated development sites. This information can then be used by project partners and the local planning authority so that strategic planning decisions can take account of flood risk. It should be noted that areas identified for development could be subject to change as the planning process progresses. For example, the Rye Neighbourhood Plan is currently ongoing and one of the objectives of this study is to identify sites for housing.

4.1 Local Development Framework

Rother District Council have undertaken a Strategic Housing Land Availability Assessment (SHLAA) across the district. This is a technical assessment of sites that have potential for housing development. The assessment concludes if the sites are suitable for development (green), have some restrictions against development (amber) or are not suitable for development (red). In 2013, Rother DC published a review of their SHLAA4. This document identified sites for development and dates of key milestones. Rother District Council provided the green and amber SHLAA sites identified within Rye and these are shown in Figure 4-1. In addition, sites where more than 10 units have been granted planning permission, development sites allocated in Rother District Council’s Local Plan and areas were broad scale redevelopment could be undertaken are also identified on Figure 4-1.

Figure 4-1: Strategic development areas identified in Rye.

Table 4-1 lists all the SHLAA sites identified in Rye and the planned land use.

SDA Purpose Location

Green Sites

RY18 Redevelopment - mixed use Land in the south of Tilling Green Estate

RY7 Urban infill - residential provision Land in the centre of Rye, Cyprus Place

RH1 Redevelopment – residential use Land adjacent to Stonework Cottages

Amber Sites

4 Rother DC (2013) Strategic Housing Land Availability Assessment (SHLAA0 2013 Review Part 2 – Settlement Maps

and Tables

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SDA Purpose Location

RH9 Urban extension - mixed use Land to the south of Rye Harbour

RY19a Redevelopment - mixed use Land south of Kings Ave and New Road

Large Site Commitments

RY50 25 units with planning approved St Bartholomew’s Court

RY44 6 units with planning approved Tower House, Hillders Cliff

RY20 10 units with planning approved 53 Cinque Ports Street

RY41 55 units with planning approved Udimore Road

RY5

Broad Locations

RY53 Redevelopment - mixed use Land adjacent to Winchelsea Road

RY36 Redevelopment - mixed use Land East of Gateborough Farm, Winchelsea Road

RY3 Redevelopment - mixed use Land between South Undercliff and Rock Channel

Table 4-1: Strategic development areas allocated in Rye

4.2 Development areas in priority areas

In line with the National Planning Policy Framework (2012) local planning authorities should prepare a Strategic Flood Risk Assessment5 (SFRA) as part of the evidence base supporting the development of their local plans.

The land to the north of Gibbet Marsh (RY18) has been identified as an area for redevelopment. This area falls within the Tilling Green Estate priority area. The exact area for redevelopment has not yet been defined. As a result there is an opportunity to plan the redevelopment with the view to address the existing flood risk issues. The uFMfSW shows high risk of surface water flooding throughout the proposed redevelopment site for all return periods and on the Mason and Cooper Roads adjacent to the site. There is also recorded sewer flooding and a highway drainage induced flood incident nearby.

Land in the centre of Rye, north of Wish Street and south of Ferry Road has been highlighted for infill (RY7). This is not in a priority area as defined in the SWMP. However, the uFMfSW shows pluvial ponding immediately next to the site and a flow path down Cyprus Place, both on the western side of the site. As the exact area for redevelopment is not defined yet there is opportunity to plan development in conjunction with managing flood risk.

The land in the south of Rye Harbour, adjacent to Oyster Creek (RH9) has been identified as a potential area for development. There are no flooding incidents recorded nearby however this may be due to low receptor density. Within RH9 there is one small area identified by the uFMfSW to be at risk during a 1000 year return period event.

The land in the east of Rye, abutting New Road is not in a priority area and is not at risk of surface water flooding according to the uFMfSW.

Urban intensification could exacerbate the existing pluvial runoff problem. Furthermore, increasing the number of properties connected to the foul sewer network would increase the risk of manhole flooding. However, development can present opportunities to upgrade sewer infrastructure or reduce surface runoff by incorporating SuDS.

It should be noted that a Flood Risk Assessment (FRA) is a requirement for any planning application of an area greater than one hectare. Therefore, the effect of flood risk should be assessed prior to development. Furthermore, the LLFA must be consulted on applications for major development and their impact on local flood risk.

5 Department for Communities and Local Government (2012) National Planning Policy Framework. www.communities

.gov.uk

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5 SWMP action plan This section sets a plan for managing the flood risk identified in this SWMP. The action plan uses all the information collated during the SWMP process to recommend measures to reduce or mitigate the flood risk in Rye. The actions have been developed according to the flood mechanism.

5.1 Monitoring the action plan

It is proposed that the monitoring and reporting of the implementation of the action plan will be undertaken locally and it is expected that partners will take forward actions independently, and convene as and when appropriate.

5.2 Communicating the action plan

The action plan is divided into three components, each of which look at mitigating flood risk at a different scale. The three actions components are; the generic action plan, the priority area action plan and the incident specific action plan. The spatial coverage and purpose of each action plan is explained in Table 5-1.

Geographic area Action Plan Purpose

Study area wide Generic action plan (section 5.3)

Outline broad scale actions applicable across the study area

Specific streets within priority areas

Priority areas (section 5.4) Recommend strategic actions to manage the flood risk in priority areas

Specific points where flooding has been reported

Incident specific action plan (section 5.5)

Propose specific activities in response to a reported flood incident

Table 5-1: Action plans

5.3 Generic action plan

Some of the actions derived during this SWMP are applicable to multiple or all flood points in Rye. Action to mitigate these issues are listed in the generic action plan.

5.3.1 On-going maintenance of the partnership

To successfully undertake the action plan and continue to improve the management of flood risk in the area, it is important to maintain the links between the risk management authorities involved in the production of the SWMP. The on-going partnership will discuss the implementation of the proposed actions, review opportunities for operational efficiency and to review any legislative changes. It is proposed that the monitoring and reporting on the implementation of the action plan will be undertaken locally.

5.3.2 Planning

The SHLAA green sites identified as RY7 and RY18 are located nearby areas of Rye which have been identified by this SWMP as having suffered extensive or frequent flooding in the past. It is recommended that the planning authority incorporate the findings of this SWMP and thereby raise issues to developers through its local plan to allow for pre-emptive flood risk reduction during the planning process.

5.3.3 Asset maintenance

Currently East Sussex highways are revising their asset maintenance programme. The objective is to optimise their routine asset inspection and maintenance to prevent flooding occurring as a result of malfunctioning gullies. This change in programme could have benefits across Rye. In particular, it is recommended that North Salts be considered for an enhanced cleansing regime due to its flood history.

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5.3.4 Further study

This SWMP has found the Winchelsea Road area to be susceptible to flooding from both surface water and sewer flooding. Preliminary investigation has found that this flooding is not as a result of blockage or malfunctioning assets. Therefore, detailed CCTV survey and hydraulic modelling is required to fully understand the integrated flood mechanisms in this location. Therefore, it is recommended that further investigatory work is undertaken in this area. This should include an option appraisal to inform flood mitigation measures.

5.3.5 Using SuDS

Surface water flooding is exacerbated by urbanisation. This is because natural, permeable land uses are replaced with impermeable surfaces. Sustainable drainage systems (SuDS) mimic natural systems and provide solutions to surface water runoff and pollution. As such, using SuDS in Rye could help mitigate the surface water flooding.

SuDS is an overarching term for various surface water management devices. The devices perform tasks such as capturing rain water, retaining surface water or filtering pollutants and some SuDS techniques are multipurpose. Together, the sequence of SuDS components form a SuDS management train.

SuDS components fall into three general categories; source control, retention and infiltration.

In April 2015, East Sussex County Council (ESCC) became a statutory consultee on planning applications. In preparation for this role, ESCC partnered with other South East 7 Lead Local Flood Authority to prepare the SuDS guidance document - ‘Water. People. Places’, which encourages the integration of SuDS into the development layout. An additional local guidance document, setting SuDS into an East Sussex context is under development. Together these two guidance documents will be adopted as County Council policy on SuDS, supporting and assisting the delivery of the Local Flood Risk Management Strategy.

Source control

Source control SuDS can be fitted or retrofitted to individual properties and intercept rainwater as it falls either absorbing a percentage of it upon impact, as in the case of green roofs; or storing rainwater in water butts, connected to a drain pipe, for later use. For the most effective runoff reduction, both of the above methods should be used in conjunction. Other measures of source control include permeable paving, a replacement to impervious surfaces such as tarmac, which allows water to infiltrate and reduce surface runoff. Due to the topographic variation in Rye, permeable paving is feasible in areas of flatter topography as this allows for low velocity runoff which promotes surface water to permeate into the subsurface as opposed to continuing overland. However, it should be considered that much of the flatter areas of Rye are reclaimed marsh land and as a result have potential for a high water table. Therefore, source control measures which rely on infiltration should consider the use of a permeable substrate. In areas with higher slope gradients runoff will move at a higher velocity and permeable paving will prove ineffective. Green roofs and rainwater harvesting would also be an effective source control method in this area.

Southern Water offers a rebate to customers if they remove their contribution to the surface water sewer system. Therefore any customer who operates source control could benefit financially. Furthermore, under the "your water meter" campaign Southern Water offer a 20% discount on water butts to private residents and free water butts to schools and community groups. One disadvantage of using source control as a surface water mitigation measure is that it is reliant on public engagement and uptake of the scheme.

Retention

Adopting retention SuDS could temporarily store water and therefore delay the catchment response, producing a lower but more prolonged peak water level in the watercourses. Applying a retention SuDS action could reduce flooding from both surface water and fluvial sources.

However, retention SuDS devices, such as detention basins and retention ponds, require space and could be employed in open spaces dependent upon the local geology. Retrofitting retention devices, to housing estates for example, is typically impractical; as unless considered during the planning process, large unused open spaces are usually unavailable. Strategic Housing Land Availability Assessment areas have been identified in Rye and these present an opportunity to consider retention SuDS at planning stage.

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Infiltration

SuDS that infiltrate into the ground rely on the subsurface to accept and store surface water. Therefore, the physical properties of the ground are important when selecting where infiltration SuDS are appropriate. The geology underlying Rye is the Ashdown formation part of the Wealden Group. The Ashdown formation in the area comprises of sandstones, siltstones and mudstones. The uppermost layer is sandy and allows for some infiltration. The bedrock geology is however overlain in large areas, particularly in the south of Rye, by clays and silts which may hinder infiltration dependent upon their spatially variable permeability.

In addition, there is potential for high water table levels especially in the marsh land surrounding the town. Therefore, it is suspected that the effectiveness of infiltration SuDS will be limited for the majority of Rye. However, local infiltration testing is recommended to ascertain if infiltration SuDS are a viable option on a case by case basis.

5.4 Priority areas

For the priority areas identified in section 3, strategic options have been recommended to address integrated flood mechanisms operating in these areas.

5.4.1 The Strand

The Strand is the highest priority area in Rye as the flood volumes could endanger the public; the sewage load in the flood water is a potential health hazard and if it was not for people protecting their homes with sandbags, this flooding would have caused internal damage to houses.

Southern Water has already undertaken provisional investigations to check their network is clear of blockage and that their ancillaries are operating correctly. The investigation did not find any operational cause for the sewer flooding. However, the volume of flooding witnessed at this location is unlikely to be caused by surface water infiltration alone. It could also be that tidal ingress to the sewerage network is occurring where flap valves are missing at sewer outfalls in the River Tillingham. However, this can only be confirmed through detailed investigation.

It is recommended that further investigations are undertaken to understand the cause of sewer flooding at this location. Following establishing the root cause of the flooding, an options appraisal should be undertaken to understand what measures would reduce flood risk here. Options to investigate could include pump optimisation, replacing flap valves on existing assets or installing a combined sewer overflow from the flooding manhole directly to the River Rother. If no feasible option is found, property level protection should be provided to residents on Winchelsea Road. The location of these proposed actions is shown in Figure 5-1.

Figure 5-1: Action plan for The Strand

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5.4.2 Tilling Green estate priority area

The flood risk and flood history show that highways of the Tilling Green estate are susceptible to surface water. The flooding issue at Tilling Green estate has been improved by recent renovation of the Southern Water surface water pumping station on Marley Road.

The opportunity for adopting SuDS to infiltrate surface water is limited due to the water content of the underlying soils which is reclaimed marsh land. Therefore, positively drained pipe networks are the only effective measure of surface water removal at Tilling Green. As a result, it is recommended that maintenance of highway drainage is prioritised in Tilling Green estate as it is understood that there is no viable alternative for draining surface water.

During the site inspection, some signs of highway subsidence was observed. Subsidence could disrupt the piped networks creating cracks. Due to the high water table, if there are any defects in the network, it is likely that infiltration will occur. In the future, investigation into sewer condition could be required using CCTV survey.

The location of each of these actions is shown in Figure 5-2 below.

Figure 5-2: Action plan for Tilling Green estate

Development site sub area

It is recommended that the site masterplan is designed considering the existing surface water flood risk as shown in the uFMfSW.

In addition, it is strongly advised that the flood risk from the Old Brickyard Culvert is understood prior to construction. Investigation could include further CCTV and dye tracing to ascertain where the current inflow is going.

In terms of mitigating the risk, there is potential for constructing an open diversion channel along the southern boundary of the site to bypass the culvert which is suspected to have a significant defect. This approach would prevent flow leaking from the pipe and gradually waterlogging the local soils, which would have a detrimental effect to the foundations. However, the developer should be aware of the ongoing responsibilities of riparian ownership. This is especially pertinent as current plans see the construction of social housing, where the developer would become landlord and land owner.

The location of the proposed bypass channel is shown in Figure 5-3.

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Figure 5-3: Action plan for Tilling Green School development site

5.4.3 North Salts priority area

The slope from Rye Hill is currently quite highly vegetated. Therefore, there are no simple measures to manage the sediment load. As a result, it is recommended that North Salts is considered for priority maintenance by the highway authority to allow the drainage system to run free and clear. This action is illustrated by Figure 5-4.

Figure 5-4: Action plan for North Salts

5.4.4 The Grove priority area

As the flooding is relatively low frequency and has not resulted in internal property flooding, the Grove is a relatively low priority area in relation to those elsewhere in the county. However, while on site we observed some potential quick wins for managing the flood risk. For example, the open channel which runs through the sports centre carpark, towards the scout hut, is very overgrown and has become quite silted. As the surface water drainage from the carpark

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discharges to this watercourse it is recommended that the vegetation is cleared to improve conveyance. In addition, the watercourse could be de-silted to improve the capacity of the channel.

It is understood that the highway culvert under The Grove has blocked on multiple occasions causing fluvial flows to pond upstream on the private land east of the road. It is recognised that this flooding is a nuisance to the landowner, but at this time it is not recommended that any action is undertaken to upsize the highway culvert. This is because current flooding issues downstream of the culvert suggest there is insufficient capacity in the current drainage network to receive additional flows. In fact, throttling the flows to the east of The Grove could be contributing to managing the risk of flooding downstream, to properties on The Grove and the schools. However, it is important to maintain clear through flow of this pipe to prevent flood water overtopping The Grove highway.

The fluvial flows in this priority area drain to the River Tillingham via a gravity or a pumped outfall. The fluvial pump is owned and operated by Rye Primary School. At the time of writing, it is not clear under what conditions the pump would operate; the latest survey found the pump was in good condition. Currently, restricted fluvial discharge to the Tillingham is not considered the primary mechanism leading to flooding. However, if future flood incidents relate to this, there is an opportunity to conduct pump tests to better understand the pump regime to determine if it is possible to optimise pump operation for managing flood risk further upstream. The location of these proposed actions is shown in Figure 5-5.

Figure 5-5: Action Plan for The Grove

5.5 Incident specific actions

A suitable action has also been set for every flood incident on the Rye flood history table. The unique ID allocated to each flood incident has also been used in the site specific action plan for cross referencing. A full list of actions is available in Appendix E.

To enable effective delivery of the action plan, it has been colour coded according to priority. The prioritisation process considered

the date of the last recorded incident;

the frequency of recorded flooding; and

the vulnerability of the receptors.

There are four classifications of action priority: high, medium, low and complete. All of the high priority actions correspond to recent flood records which have a high frequency or affect a more vulnerable receptor. The medium priority can be older records, if the incident has a high frequency or vulnerable receptor. The low priority actions refer to one off flood events, generally

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old records and low vulnerability receptors. The completed actions have been added to include where work has already been undertaken, to avoid duplicating efforts.

5.6 Way forward

Whilst East Sussex County Council has taken the responsibility for leading on the Stage 1 SWMP, it is recommended that the responsibility for monitoring the progress of the action plan and maintaining the links between the partners would be better served at the local level. Thus the immediate next step should be to agree who will lead the delivery of the action plan and the continuation of the partnership.

It is also recommended that the progress of the SWMP to the more detailed stages should be focused on the areas where repeated flood incidents have been recorded together with high predicted flood risk. For the Rye SWMP, further detailed assessment is recommended on Winchelsea Road.

In addition to the progression of the SWMP process, the Stage 1 SWMP has also identified a need for the establishment of a programme of ‘preventative maintenance measures’ for highway drainage, suggesting critical areas for prioritisation.

Finally, as part of an iterative process of revision, the outputs of the SWMP should be incorporated into future revisions of the East Sussex Local Flood Risk Management Strategy.

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Appendices

A Appendix - Data Quality Score

B Appendix – Flood History Table

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C Appendix – Quantifying Surface Water Flood Risk

Group name Sub-class

Ambulance Station AMBULANCE STATION

Education ADULT EDUCATION

EDUCATION

FIRST SCHOOL

FURTHER EDUCATION

FURTHER EDUCATION COLLEGE

HIGH SCHOOL

HIGHER EDUCATION

INFANT SCHOOL

JUNIOR SCHOOL

MIDDLE SCHOOL

NURSERY

PRIMARY SCHOOL

PRIVATE PRIMARY SCHOOL

SCHOOL

SCHOOL FOR THE DEAF

SECONDARY SCHOOL

SPECIAL SCHOOL

TECHNICAL COLLEGE

UNIVERSITY

PRE SCHOOL EDUCATION

Electricity ELECTRICITY GENERATING

ELECTRICITY SUB STATION

Fire Station FIRE STATION

Gas GAS DISTRIBUTION

GAS MONITORING

GAS PRODUCTION AND DISTRIBUTION

GAS REGULATING

GAS STORAGE

Health DAY CARE

HOSPICE

HOSPITAL

MENTAL HEALTH CENTRE

NATIONAL HEALTH SERVICE WALK IN CENTRE

NURSING HOME

MEDICAL SERVICES

MORTUARY

SURGERY

Police POLICE HEADQUARTERS

POLICE STATION

POLICE SERVICES

Waste Water SEWAGEFILTRATION

SEWAGEOUTFALL

SEWAGEPUMP HOUSE

SEWAGEPUMPING

SEWAGERECYCLING

SEWAGESTORAGE

SEWAGETREATMENT

Water Treatment WATER TREATMENT

PUMP HOUSE

Coastguard HM COASTGUARD RESCUE

HM COASTGUARD SERVICES

Socially vulnerable RETIREMENT HOME

REST HOME

RESETTLEMENT CENTRE

HM DETENTION CENTRE

HM PRISON

HM YOUNG OFFENDERS INSTITUTION

CHILD DAY CARE

CHILDRENS HOME

CHILDRENS NURSERY

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D Appendix – Using the GeoPDF GeoPDFs have been used as the vehicle to communicate risk and flood history. The advantage of using maps is that a lot of data can be displayed in a manner which is easily viewed. The advantage of using a PDF is that it cannot be edited. A GeoPDF embodies both advantages and in addition, enables some basic GIS software functionality. A GeoPDF can be opened in any PDF viewer, software which is freely available.

The GIS functionality includes selecting layers to switch off or on, and jumping between map extents and attribute tables. It was important to this study that the GeoPDF be simple to use for communications with non GIS using project partners. An introduction page was also built in to explain how the GeoPDF works.

D.1.1 Data displayed

The GeoPDF summarises all the relevant data collected as part of this study. This includes recorded flooding, predicted flood risk and catchment data such as mapping. The GeoPDF produced for all of Rye is shown in Figure D-1.

Figure D-1: The GeoPDF flood risk and recorded flooding incidents in Rye.

The GeoPDF summarises all the relevant data collected as part of this study. This includes, recorded flooding, predicted flood risk and catchment data such as mapping Details of the data included on the GeoPDF are listed below.

D.1.2 Flood history

The flood history points have been compiled from all the data received. The source-pathway-receptor model was applied to each point and the total number of repeated flood incidents was tallied. This enabled the point to be thematically mapped. The colour of the flood point was dependent on the flood source, whereas the size of the flood point was dependent on the frequency of the flood incidents recorded at that location, from the same source. The colour coding and scaling allows a lot of data to be communicated simultaneously, in a clear and decipherable way. The colour coding addresses objective 6 as clusters of flood history points of different colours indicates flood risk combined sources. The scaling of flood history points by frequency address objective 4 as large flood points indicate flood prone areas.

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The flood sources are descriptive of both the type of flooding (e.g. fluvial) and the type of asset (e.g. highway culvert). This sub division has been made so that the Risk Management Authority (RMA) responsible for the flooding incident is easily identified.

All the flood sources used in Rye SWMP are listed in Table D-1. This also includes the colour coding system used in each of the GeoPDFs.

Flood Source Symbol

Surface Water: private drainage

Surface Water: pluvial runoff

Surface Water: highway drainage

Surface Water: drainage ditch

Groundwater

Fluvial: ordinary watercourse

Sewer: Surface water network

Sewer: Foul network

Other Flooding Source

Table D-1 Source of flooding colour coding system

Size of points depends on number of instances. The number of recorded incidents has been divided into three categories:

A low frequency event with only one or two incidents is represented by a small point;

A mid frequency event with three to four incidents recorded is represented by a medium point; and

A high frequency event with five plus incidents is represented by a large point.

This scaling system has been added to the GeoPDF to instantly show reoccurring flood mechanisms. This helps to prioritise actions.

D.1.3 Flood risk data

The predicted flood risk from surface water is represented by the updated Flood Map for Surface Water (uFMfSW). The return periods displayed are the 30, 100 and the 1000yr.

A groundwater flooding potential layer has been added to the GeoPDF for reference and outlines three levels of potential: Limited potential, potential for flooding of below ground level property and potential for groundwater flooding at the surface. This has been used in place of the Areas Susceptible to Ground Water Flooding (AStGWF) dataset as the resolution is higher; the AStGWF analysis is based on a 1km grid.

D.1.4 Catchment layers

Additional mapping layers have been added for context. These include the Detailed River Network (DRN) which shows all watercourses. Areas allocated for development, labelled with the SHLAA reference number. Finally a study boundary delineating the areas of interest has been marked.

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E Appendix - Incident specific action plan

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