Hailsham and Hellingly 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

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 / March Tom Schindl (East Sussex N/A 2015 County Council) Tom Schindl (East Sussex Final Report v2 / April 2015 Address comments from TS County Council) Tom Schindl (East Sussex Final Report v3 / April 2015 Address comments from TS County Council) Address comments from the Tom Schindl (East Sussex Final Report v4 / June 2015 project steering group County Council) Contract This report describes work commissioned by Tom Schindl, on behalf of East Sussex County Council, by an email dated 6th August 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-Little 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 Wealden District Council, Southern Water, the Environment Agency and East Sussex County Council for all their assistance during this project.

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 water runoff, groundwater, and ordinary watercourses. SWMPs are led by a partnership of flood risk management authorities who have responsibilities for aspects of local flooding. The partnership can include the County Council, District Council, Environment Agency, Sewerage Undertaker, Internal Drainage Board and other relevant authorities. East Sussex County Council as Lead Local Flood Authority (LLFA) has led the production of Hailsham and Hellingly Stage 1 SWMP in partnership with Wealden District Council, the Environment Agency and Southern Water. 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 plan will be undertaken locally and it is expected that partners will take forward actions independently, and convene as and when appropriate. Hailsham is a traditional market town in the south of the Wealden district which has undergone continued growth since the 1970's. Hellingly is a small village located 1.5 miles north of Hailsham. The approved local plan for Hailsham provides for 1,300 new homes to be built in the period leading up to 2027. Much of this growth is planned for the corridor between Hailsham and Hellingly. The mixed impermeable geology of the Wealden Group, coupled with increasingly intense urbanisation and sometimes steep relief creates conditions for high surface water flood risk in Hailsham and Hellingly. To better understand flood risk in Hailsham and Hellingly 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:  Harebeating Stream catchment, which includes three sub areas of specific concern: Woodlands Close, Harebeating Crescent and Harold Avenue;  Horse Eye Sewer catchment, which includes two sub areas of specific concern: Station Road and Butts Field; and  Knockhatch Stream catchment, which includes the Diplocks housing estate and the Diplocks trading estate. 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 Hailsham and Hellingly, 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 Hailsham and Hellingly include:  commission a CCTV survey to understand the route and condition of the culverted streams in the Harebeating Stream priority area;  address the fly tipping issue in Hailsham at Butts Field in the Horse Eye Sewer priority area and Danum Close in the Harebeating Stream priority area; and  target highway gully maintenance on Station Road in the Horse Eye Sewer priority area. As there is significant growth planned for Hailsham, much of it falling within the topographic catchment of Harebeating Stream; there is the potential for these developments to be at risk of flooding and/or exacerbate the existing problem. Consequently, it is recommended that Wealden District Council incorporate the SWMP findings into their own local plans.

List of Figures Figure 1-1: SWMP study area depicting the location of watercourses ...... 9 Figure 1-2: Conceptualisation of the integration of flooding mechanisms...... 10 Figure 1-3: The underlying geology of Hailsham and Hellingly...... 11 Figure 3-1: Flood history in Hailsham and Hellingly ...... 19 Figure 3-2: Main river flood risk ...... 21 Figure 3-3: uFMfSW in Hailsham and Hellingly ...... 22 Figure 3-4: Frism output for the total number of receptors affected by surface water flooding in a 1 in 1000 year return period...... 24 Figure 3-5: Groundwater flood risk in Hailsham and Hellingly ...... 25 Figure 3-6: Priority Areas identified in Hailsham ...... 26 Figure 3-7: Harebeating Stream priority area ...... 27 Figure 3-8: Identified watercourses in the Harebeating Stream priority area...... 28 Figure 3-9: Flood incidents and mapped drainage assets on Woodlands Close ...... 29 Figure 3-10: Flood history at Harebeating Drive...... 30 Figure 3-11: Flood incidents and mapped drainage assets on Harold Avenue ...... 31 Figure 3-12: Horse Eye Sewer priority area ...... 32 Figure 3-13: Knockhatch Stream priority area ...... 33 Figure 4-1: Strategic Development Areas identified in Hailsham and Hellingly...... 35 Figure 5-1: Action locations on Woodlands Close ...... 40 Figure 5-2: Action map for Harebeating Drive ...... 41 Figure 5-3: Action locations on Harold Avenue ...... 42 Figure D-1: The GeoPDF flood risk and recorded flooding incidents in Hailsham and Hellingly...... VI

List of Tables Table 2-1: Partners involved in the SWMP process ...... 14 Table 2-2: Catchment data and data supplier ...... 15 Table 2-3: Flood risk modelling data and supplier ...... 15 Table 2-4: Data quality scoring system ...... 16 Table 2-5: Received data and allocated quality score ...... 16 Table 3-1: Number of receptors in Hailsham and Hellingly at risk from surface water flooding ...... 23 Table 3-1: Source-Pathway-Receptor model for Woodlands Close ...... 29 Table 3-2: Source-Pathway-Receptor models for Harebeating Stream ...... 30 Table 3-3: Source-Pathway-Receptor model for Harold Avenue ...... 30 Table 3-4: Source-Pathway-Receptor model for Station Road ...... 32 Table 3-5: Source-Pathway-Receptor model for Butts Field ...... 33 Table 5-1: Action plans ...... 37 Table 5-2: Summary of actions on Harebeating Stream ...... 39 Table 5-3: Action summary for Woodlands Close ...... 40 Table 5-4: Action summary for Harebeating Drive ...... 41 Table 5-5: Action summary for Harold Avenue...... 42 Table C-1: Receptors considered as critical infrastructure ...... IV Table D-1 Source of flooding colour coding system ...... VII

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 FRA ...... Flood Risk Assessment IDB ...... Internal Drainage Board IDD ...... Internal Drainage District LLFA ...... Lead Local Flood Authority LFRMS ...... Local Flood Risk Management Strategy NLPG ...... National Land and Property Gazetteer NPPF ...... National Planning Policy Framework NRD ...... National Receptors Database PEM ...... Public Enquiry Manager RFCC ...... Regional Flood and Coastal Communities RMA ...... Risk Management Authority SDA ...... Strategic Development Area SFRA ...... Strategic Flood Risk Assessment SIRF ...... Sewer Incident Report Form SuDS ...... Sustainable Drainage Systems SWMP ...... Surface Water Management Plan uFMfSW ...... updated Flood Map for Surface Water

Executive Summary ...... 2 List of Figures ...... 3 List of Tables ...... 4 Abbreviations ...... 5 1 Introduction ...... 7 1.1 What is a surface water management plan ...... 7 1.2 Summary of aims and objectives ...... 7 1.3 Stages of SWMP development ...... 8 1.4 Sources of flood risk ...... 8 1.5 Study area ...... 11 2 Preparation ...... 14 2.1 Partnership approach ...... 14 2.2 Data collation and review...... 14 3 Strategic assessment ...... 17 3.1 Flood history ...... 17 3.2 Flood risk ...... 19 3.3 Priority areas ...... 25 4 Planning ...... 35 4.1 Local Development Framework ...... 35 4.2 Development areas in flood hotspots ...... 36 4.3 Planning policy ...... 36 5 SWMP action plan ...... 37 5.1 Monitoring the action plan...... 37 5.2 Communicating the action plan ...... 37 5.3 Generic action plan ...... 37 5.4 Priority areas ...... 39 5.5 Incident specific actions ...... 43 5.6 Way forward ...... 43 Appendices...... I A Appendix - Data Quality Scores ...... I B Appendix - Flood History Table ...... II C Appendix - Quantifying Surface Water Flood Risk ...... III D Appendix – Using the GeoPDF ...... VI E Appendix - Incident Specific Action Plan...... VIII

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 water 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, Sewerage Undertaker, Internal Drainage Boards and other relevant authorities. Hailsham and Hellingly have been identified as areas 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 actions 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 Hailsham and Hellingly 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 aims and objectives The aims and objectives of the Hailsham and Hellingly Stage 1 SWMP are: 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 date, 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; and 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.

1.3 Stages of SWMP development The SWMP will be prepared across a series of three stages, as follows:  Preparation: Building a partnership of risk management authorities (RMAs). Gathering evidence of and information about flooding.  Risk Assessment: Undertaking a coarse assessment of flood risk to determine the highest risk locations and the key issues upon which the action plan should focus, using publicly available datasets in combination with local records of flooding.  Action Plan: Preparation of an action plan that recommends a range 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 rivers 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 (see section 1.5.1), 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. Hailsham is situated in the Cuckmere River valley. The Cuckmere runs across the north of the study area. Tributaries to the Cuckmere which also flow through the study area include Knockhatch Stream, Bull River and Horsebridge Stream. The east of the study area drains towards the Saltmarsh Sewer and away to the Pevensey Levels. The Harebeating Stream is of considerable importance as new development is proposed in the area, and investigations indicate that an ordinary watercourse originating from the Hawythlands area in fact may follow the stream’s historic course and connect into the Harebeating Stream rather than going east towards the Whelpley Sewer as indicated in the Environment Agency’s detailed river network map layer. This issue is discussed in greater detail in Section 3.3.1. Ordinary watercourses An ordinary watercourse is a statutory type of watercourse in England and Wales. They include rivers, streams, ditches, drains which do not form part of a main river. Wealden District Council has permissive powers to carry out works on ordinary watercourses. ESCC has responsibilities in relation to consenting and enforcement. In addition to the main river network across the study area, there are also a number of smaller streams and drainage networks which drain into main rivers. In particular, the upper reaches of the Harebeating Stream, Whelpley Sewer and the Horse Eye Sewer flow through residential areas. Figure 1-1 (below) details the location of the main rivers and ordinary watercourses in the vicinity of Hailsham and Hellingly based on EA’s detailed river network (DRN) mapping. In this figure, the DRN for the Harebeating Stream has been amended to follow the course to old maps as our site investigation showed the culverted watercourse had been inaccurately mapped. There is more information on this in Section 3.3.1.

Figure 1-1: SWMP study area depicting the location of watercourses

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 waste water. Surface water sewers convey collected pluvial runoff and combined sewers convey a mix of both foul water and surface water. Southern Water is responsible for the sewer networks in this area. As partners in the SWMP process, Southern Water has provided records of their assets in Hailsham and Hellingly. The area is served by two Wastewater Treatment Works (WTW) situated in the north and south of Hailsham which discharge into the Pevensey Levels. The area is largely served by separate sewerage systems, with a foul network to convey trade and household waste water and a surface water sewer system to convey runoff; however there are some small areas utilising a combined network. 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 may be caused by flooding 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. 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 quality of water.

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 highways drains and gullies, open channels, ordinary watercourses and SuDS).

1.4.4 Integrated flood risk In an urban environment such as Hailsham and Hellingly, flooding mechanisms are closely integrated. The flood mechanisms that operate in Hailsham and Hellingly 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 Hailsham is a traditional market town in the south of the Wealden district which has undergone continued growth since the 1970's. Hellingly is a small village located 1.5 miles north of Hailsham. The approved local plan for Hailsham provides for 1,300 new homes to be built in the period leading up to 2027. Much of this growth is planned for the corridor between Hailsham and Hellingly, which would result in the geographical boundaries between the two areas becoming less distinct. Figure 1-3 illustrates the geology of the study area. The underlying bedrock geology of the area is the Weald Clay formation part of the Wealden Group. The Weald Clay formation in the area comprises of bedded mudstones with intermittent siltstone, sandstones, limestones and clay ironstones. The bedrock geology is however overlain in areas in the north with river terrace deposits (sand and gravel); and to the south and east with Alluvium (clays, silts and sands) which may aid infiltration or exacerbate surface water runoff dependent upon their spatially variable permeability. Coupled with increasingly intense urbanisation this presents conditions for increasing flood risk in Hailsham and Hellingly.

Figure 1-3: The underlying geology of Hailsham and Hellingly.

Hailsham spans two topographic catchments. The west of Hailsham and Hellingly drain towards the Cuckmere River. Therefore, any runoff or sediment load created in west Hailsham and Hellingly should pass through Arlington and Alfriston and outfall to the sea near Seaford. Whereas the east of Hailsham drains towards the Pevensey Levels before discharging to the sea at Pevensey. The Environment Agency have modelled the Cuckmere River. However, there are a number of unmodelled watercourses radiating from Hailsham which are both main river and ordinary watercourses.

1.5.1 Catchment Flood Management Plan A Catchment Flood Management Plan (CFMP) is a high-level planning strategy document 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 fluvial flood risk. The proposed actions relevant to Hailsham and Hellingly are:  Work with Wealden District Council to influence spatial development with the aims of ensuring no net increase in run-off from new developments (including the use of SuDS) and to ensure adequate foul and surface water infrastructure is available before new development.  Work with Wealden District Council and the water companies to develop a surface water management plan, with review of receiving watercourses/catchments, foul and surface water, and consider the effects of climate change. The production of this document satisfies this action.

1.5.2 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 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 how and if flood risk from different sources combine to produce a flood event. As there are eight main rivers within the Hailsham and Hellingly study boundary, the fluvial flood maps are applicable to this SWMP. Surface Water There are three sources of information available from the Environment Agency relating to the identification of potential surface water flood risk in Hailsham and Hellingly. These 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 to provide a more accurate representation of surface water flood risk across England and Wales. As the uFMfSW is the most up to date and detailed dataset available, it forms the basis of the surface water flood risk assessment.

Groundwater Two sources of data were provided by ESCC relating to the identification of potential groundwater flood risk is Hailsham and Hellingly. 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 emerge1. 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.

1 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

2 Preparation

2.1 Partnership approach Within Hailsham and Hellingly, 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 manage flooding issue. As such, partnership working is a key emphasis in East Sussex's SWMP process. To fully understand flood risk in Hailsham and Hellingly 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 actions. 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 Hailsham and Hellingly SWMP are listed in Table 2-1.

Organisation Representative(s) East Sussex County Council as LLFA Nick Claxton, Tom Schindl, and Fiona Hartland Wealden DC Drainage Engineer Graham Kean East Sussex County Council as Highways Nathan Morton-Clarke and Tom Crawshaw Agency Environment Agency Peter Aimes Southern Water Mike Tomlinson

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. In addition to the above Wealden District Council planning department was also involved in the SWMP. WDC planning is not responsible for managing flood risk but it does hold information useful to the SWMP. Furthermore, as the authority responsible for setting local planning policy, they hold the power to advise developers and shape sustainable and flood resilient future development. Natalie Bumpus (Planning Officer) represented Wealden planning

2.2 Data collation and review In collaboration, 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, are fluvial flooding points 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 the table below.

East Sussex County Council Environment Agency Bedrock and superficial deposits geology LIDAR (under licence from BGS) Main river centreline Detailed River Network (DRN) Gully point locations 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 in shown in Table 2-3.

Environment Agency East Sussex County Council Areas susceptible to ground water flooding Updated flood map for surface water: 30, 100 and 1000 year return periods ESI Groundwater Flood Risk Fluvial flood map: 100 year and 1000 year return periods

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: Wealden District Council Land Drainage Database; 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 Hailsham and Hellingly 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 Hailsham and Hellingly 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 nothing to distinguish between value of the data sources. Therefore, a refined scoring system was developed to provide a more informative data score.

Data Sub-category Quality Description Score N/A Best possible, no 1 better data available

2a) the known deficiencies are missing or duplicated data Data with known 2 deficiencies 2b) the known deficiencies are missing and duplicated data

3a) Assumptions confirmed with local data

Assumption based on 3b) Assumed data confirmed by cross referencing with other 3 available data records 3c) Assumed data based on a single dataset

Educated guess N/A 4 based on experience

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 a 3 or 4. The sub- categorisation of the data score distinguishes the relative quality of the data or the confidence in the assumption. This confidence scoring system can be applied to the received data, the source-pathway- receptor model and the selected hotspot 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 Hailsham and Hellingly SWMP and the data quality score associated with it.

Data Data Quality Score ESCC records of flooding 1 Highways PEM register 2a Wealden land drainage database 2a Southern Water SIRF 1 Fire and Rescue 2b

Table 2-5: Received data and allocated quality score

3 Strategic assessment The Stage 1 SWMP for Hailsham and Hellingly 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 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 risk. 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), blocking or altering the pathway and/or removing 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 Wealden District 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 Highways always documents 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 this data requires an element of assumption. Assumptions can be partially informed by the location of a flood point but are also based on judgement informed by experience of undertaking similar assessments. 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 Findings revealed that the most common cause of flooding recorded was of 'unknown' source. This is symptomatic of a flood report where no additional information has been recorded and it is recommended that the recording of future flood reports include details of the source as part of efforts to better understand flooding mechanisms. The next most common flood source was surface water relating to highway drainage. It should be noted here the frequency of events of this nature reflects the good record keeping by East Sussex Highways, which spans back to 1999. It is likely that the infrastructure related to the flooding incidents have subsequently been cleaned or replaced. Consequently it could be useful to have a report on the condition of the asset alongside it and the planned date of the next inspection. Surface water flooding due to pluvial runoff is the following most common flood source recorded in Hailsham. 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 large number of foul sewer flooding incidents in Hailsham. The sewer flooding event data provided by Southern Water are attributed to hydraulic overload, rather than blockage

or asset failure. This means the events are due to insufficient capacity in the sewer network. Often these are in response to rainfall, however, technically there should be no response to rainfall in the foul network as the only flow contributing is domestic and commercial waste water. Foul sewer flooding due to overload often indicates that the infrastructure is receiving unplanned flows due to misconnections, manhole inundation or infiltration of groundwater. In these instances, flood mechanisms are integrated, with sewer flooding occurring together with surface water flooding or high groundwater levels. As surface water runoff is a common flood mechanism, it is likely that the inundation of manholes is the predominate source of unplanned flows on the foul network. However, as there are large areas where Southern Water asset maps show no surface water system, there is a chance that some areas could be operated as a combined foul and surface water system. Due to the geology of Hailsham, it is unlikely that groundwater infiltration to the foul sewer is a significant issue in the catchment. The final common source of flooding is surface water flooding was attributed to inadequately maintained drainage ditches and ordinary watercourses. Hailsham contains a network of open and culverted drainage ditches which radiate from the centre of the town. The maintenance of these watercourses is the responsibility of the riparian owners and information on this is available from East Sussex2 and the Environment Agency3. However, these responsibilities are often not well understood. As a result maintenance can be neglected leading to flow obstruction. The poor condition of drainage channels, has led to flooding across Hailsham.

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.

2 http://www.eastsussex.gov.uk/environment/flooding/riparian-ownership 3 https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/403435/LIT_7114.pdf

Figure 3-1: Flood history in Hailsham and Hellingly The recorded incidents of flooding highlight that Woodlands Close, Station Road, South Road, Butts Field and Hamlins Park Close to be areas particularly susceptible to flooding. Interrogation of the data, indicates that flooding in the area is infrequently due to one source of flooding. Rather, flooding appears to be the result of a number of sources, which highlights the integrated nature of flooding in Hailsham.

3.2 Flood risk The assessment of flood risk utilised the Environment Agency’s uFMfSW as local flood risk modelling was beyond the scope of this Surface Water Management Plan. The flood risk

considered includes flooding from main rivers, surface water and groundwater, based on Environment Agency and British Geological Society data.

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 Hailsham is concentrated along the Cuckmere River. However, the town has been designed to avoid development on the Cuckmere flood plain and as a result, there are not many properties at risk of fluvial flooding from the Cuckmere. Main river flooding from the Knockhatch Stream poses a greater flood risk to people and property. However, main river risk is outside the scope of a SWMP, and therefore no detail assessment of risk has been made. Nevertheless, it is important to consider that fluvial flooding could interact with other, local flood sources at this location. Critically, flood risk around Harebeating Stream is based on dubious understanding of the course and catchment of the watercourse. Therefore it is likely that these fluvial flood extents underestimate the flood risk on Harebeating Stream.

Figure 3-2: Main river flood risk

3.2.2 Surface water As there is no local, detailed modelling available for Hailsham, the data used to inform this analysis was the updated Flood Map for Surface Water (Figure 3-3). The uFMfSW does not include the presence or effect of ordinary watercourses or drainage channels explicitly in the model. However, the uFMfSW does highlight low points and valleys in the topography as overland flow is collated and conveyed. As a result, there is some risk in ordinary watercourse valleys is indirectly accounted for.

Figure 3-3: uFMfSW in Hailsham and Hellingly The surface water flood risk in Hailsham is most noticeable along the Cuckmere River corridor. However, there are few receptors here as it makes up the fluvial floodplain. However, there is also considerable surface water flood risk along the catchment of Harebeating Stream and Knockhatch Stream (particularly in the Diplocks). It should be noted that much of Harebeating Stream is culverted in the upstream extent. Therefore, there is very limited connectivity between the surface flow path and the subterranean river. There is also a significant conveyance route for surface water along the Cuckoo Trail which is incised through the centre of the town. This passes flows onto the car park and onto Lindfield Drive and Station Road.

3.2.3 Quantifying surface water flood risk Using JBA's impact analysis software, Frism (Flood Risk Metrics), predicted flood risk to property in Hailsham and Hellingly has been quantified. 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 Extended Flood Risk Pack for East Sussex County Council, which JBA completed in 2012.

3.2.4 Quantifying surface water flood risk in Hailsham and Hellingly The analysis covers all of the study area, broken into a 250 metre grid. The receptors were extracted from the National Receptor Database (NRD). Table 3-1 displays the receptor count at risk from surface water in both Hailsham and Hellingly 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 full list see Appendix C. Return Period Critical Dwellings Emergency Total Infrastructure (NRD) responders (NRD) (NRD) 30 3 9 0 12 100 3 27 0 30 1000 17 136 0 153 Table 3-1: Number of receptors in Hailsham and Hellingly at risk from surface water flooding Analysis indicates the majority of the risk is to residential dwellings with 136 homes predicted to flood on 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 are at least 3 critical infrastructure receptors predicted to flood at all return periods and this rises to 17 in a 1000 year return. However, no emergency responders are predicted to flood during any of the return periods examined. Figure 3-4 shows the surface water flood risk to dwellings in a 1 in 1000 year return period. 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 total number of receptors affected by surface water flooding in a 1 in 1000 year return period. Figure 3-4 highlights four distinct areas where surface water flood risk affects more than five dwellings within a 250 metre cell. According to this analysis the streets with the greatest surface water flood risk to properties are Hawkstown Gardens, Hawkstown View, The Drive, Harebeating Drive, Dunbar Drive and Harmers Hay Road. The maximum number of residential dwellings predicted to be at risk during a 1 in 1000 year event in any given 250 m cell is 23 on Hawkstown Gardens and Hawkstown View. Accordingly, the designation of the flooding hotspots has been informed by this assessment.

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

Figure 3-5: Groundwater flood risk in Hailsham and Hellingly

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.

Figure 3-6: Priority Areas identified in Hailsham The priority areas often highlight areas where flood mechanisms are integrated. This demonstrates the importance of considering how flood pathways interact.

3.3.1 Harebeating Stream priority area This priority area covers the residential area within the upper catchment of Harebeating Stream (see Figure 3-7).

Figure 3-7: Harebeating Stream priority area The Harebeating Stream priority area is the highest priority area in Hailsham. The flood history is the most extensive here with the latest flood event having occurred in January 2015. The receptors in this area include residential dwellings, highways and residential curtilage. Onsite inspection identified a culverted watercourse which ran under Hawthylands Road and along Woodlands Close. The Detailed River Network (DRN) for this area did not show this culverted watercourse and instead assumed that the open channel behind Hammers Hay Road was culverted east towards Whelpley Sewer, rather than continuing to run north to Harebeating Stream. To the north of this hotspot is a second culverted watercourse draining south into the Harebeating Stream. A blockage at the upstream face of the culvert near Danum Close lead to extensive fluvial flooding in January 2015. It is understood that this blockage resulted from fly tipping. This culverted watercourse is shown in the DRN, however, the route is assumed to connect directly from two open channel sections. However, it would be expected that the route would likely to follow the course of the original stream which existed prior to housing being developed. Consequently, the actual course of the culvert is not well understood given the possibility that the watercourse could have been straightened in sections. Furthermore, the evidence of the existence of another culverted watercourse originating from the Harebeating area and running west towards Harebeating stream. Thus, it is recommended that the culverted watercourses are established and mapped via a CCTV survey. The possible route and identification of watercourses is displayed in Figure 3-8.

Figure 3-8: Identified watercourses in the Harebeating Stream priority area. N.B. the route of the identified watercourse (where culverted) is assumed from old maps. It is likely that the culverted watercourses will follow the natural channels, as this is the lowest route. However, amendments could be made to straighten any minor meanders. Therefore, the identified watercourse indicated on Figure 3-8 is only an indication of the possible route of the culvert. Consequently, ground truthing is required to verify the true course of the watercourses and if they connect with any drainage. Large scale development is planned on the fringes of this hotspot. The Strategic Development Areas (SDA) are shown in Figure 3-7. As the sites are within the topographic boundary of the Harebeating Stream catchment, any runoff generated on the new development would eventually contribute to the flow in the Harebeating Stream. The SDAs are each at different stages of the planning process, including pre-planning applications, detailed planning application and construction. Any development planned here should consider that the volume of water area contributing to the Harebeating Stream is likely to be larger than expected from the DRN. In addition, the design of any new development should be sensitive to the existing flood risk and take care not to compound the problem. Development at SDA sites could offer opportunities to improve surface water drainage systems and employ sustainable urban drainage systems (SuDS). However, if developed they could exacerbate the water level management issues in the Pevensey Internal Drainage District (IDD). The Harebeating Stream priority area covers a large area of north east Hailsham. Sub areas have been used to highlight areas where the flood history is particularly frequent or flood risk is most significant. These sub areas are Woodlands Close, Harebeating Drive and Harald Avenue which are further discussed below.

Woodlands Close sub area Woodlands Close falls within the Harebeating Stream Hotspot. There is extensive flood history here, including flooding in January 2015. The footpath to Oak Tree Way is reported to have flooded to waist deep. The Source-Pathway-Receptor model for Woodlands Close is summarised in Table 3-1 and the location of the reported flood incidents are shown in Figure 3-9. Source Surface water runoff integrated with foul sewer flooding Pathway 1. Overland flow along the road 2. Overland flow from the east (Battle Road) Receptor Residential properties, residential curtilage, highways and a footpath

Table 3-1: Source-Pathway-Receptor model for Woodlands Close Onsite inspection identified a culverted watercourse which ran under Hawthylands Road and along Woodlands Close. The Detailed River Network (DRN) for this area did not show this culverted watercourse. Previously, it had been assumed that the open channel behind Hammers Hay Road was culverted towards Whelpley Sewer, rather than Harebeating Stream. The culverted watercourse shown in Figure 3-9 has been amended according to old maps. Southern Water’s asset map is for the area is also illustrated in Figure 3-9. This does not show any surface water sewers. However, design drawings of Woodlands Close shared with us by a local resident showed surface water sewers connecting properties to this watercourse.

Figure 3-9: Flood incidents and mapped drainage assets on Woodlands Close

Harebeating Drive sub area Harebeating Drive is located within the Harebeating Stream priority area, downstream of Woodlands Close. There is considerable flood history on the road, although often the flooding source is not documented. The Source-Pathway-Receptor model for Woodlands Close is summarised in Table 3-2 and the location of the reported flood incidents are shown in Figure 3- 10.

Source Surface water runoff integrated with foul sewer flooding Pathway Overland flow along the road and culverted watercourse Receptor Residential properties, residential curtilage, highways

Table 3-2: Source-Pathway-Receptor models for Harebeating Stream Historical maps indicate that the culverted watercourse identified on Woodlands Close, continues in parallel to Harebeating Crescent before heading east along what is now Harebeating Drive towards Battle Road. It has been assumed that this route has been largely maintained during the culverting process in Figure 5-3 where the culvert is indicated.

Figure 3-10: Flood history at Harebeating Drive Onsite investigation identified an informal flood bund constructed from Tarmac separating the highway and driveways down to properties on Harebeating Crescent. If this road was to be resurfaced, the bund could be lost which would allow shallow surface water to flow towards people's homes. Therefore, it is recommended that the flood bund be reinstated if resurfacing works are undertaken.

Harold Avenue sub area Harold Avenue falls within the Harebeating Stream priority area, downstream of Woodland Close and Harebeating Drive. It is part of a new development completed in 2013. The road suffered flooding from field runoff in January 2015. The Source-Pathway-Receptor model for Harold Avenue is summarised in Table 3-3 and the location of the reported flood incidents are shown in Figure 3-11. Source Field runoff Pathway Overland flow towards the rear of properties Receptor Residential curtilage

Table 3-3: Source-Pathway-Receptor model for Harold Avenue As a recent development, the developers conformed to all current planning policy. This included a Flood Risk Assessment and limiting surface water discharge to greenfield rates. However, the properties where still flooded within one year of construction. It is understood that surface water

flooding from adjacent land was not considered a flood risk. In addition, it was noticed that the threshold of many properties were lower than the road. This is not resilient to surface water flooding.

Figure 3-11: Flood incidents and mapped drainage assets on Harold Avenue As similar development is planned in this area it is important that lessons are learnt from the example. In addition, the field where the runoff was generated is allocated for development. It is important that the impact of urbanisation on the community downstream is considered when planning the surface water drainage.

3.3.2 Horse Eye Sewer hotspot This flood hotpot covers the residential area within the upper catchment of Horse Eye Sewer (3- 9). There are three areas (Cuckoo Trail, Cuckoo Trail car park, and Station Road) within this hotspot where flooding has been repeatedly reported, these have been marked up in Figure 3-12 for reference.

Figure 3-12: Horse Eye Sewer priority area At the Cuckoo Trail car park, surface water flooding due to highway drainage has been reported. The drainage here has been specifically designed to include a throttle pipe at the discharge point to the highway drainage. This throttle pipe limits the forward discharge from the car park to prevent surface water flooding downstream. Consequently, flooding to the car park occurs when the runoff generated from the Cuckoo Trail and the car park exceed the capacity of the throttle pipe. Sub areas have been used to highlight areas where the flood history is particularly frequent or flood risk is most significant. These sub areas Station Road and Butts Field which are further discussed below.

Station Road sub area A cluster of flood history is seen on Station Road near the junction with Bell Banks Road. Most recently, this area experienced flooding in January 2015. The flood source here is surface water, attributed to pluvial run off from blocked highway drainage and surface water sewer surcharge. The Source-Pathway-Receptor model for Station Road is summarised in Table 3-4. Source Surface water Pathway Overland flow down station road towards common pond Receptor Highways and residential curtilage

Table 3-4: Source-Pathway-Receptor model for Station Road

Butts Field sub area Significant fluvial flooding has been experienced at Butts Field at a number of locations. The receptors include residential, residential curtilage and highways. It is understood that this is due to blockage of the watercourse due to persistent fly tipping causing a culvert to become blocked. Wealden District Council have attempted to manage this situation by erecting a steel fence to limit access to the watercourse. However, this has not resolved the problem, as demonstrated

by the level of trash in the system during January 2015. The Source-Pathway-Receptor model for Butts Field is summarised in Table 3-5. Source Fluvial Pathway Local fluvial exceedance due to blockage Receptor Residential properties and residential curtilage

Table 3-5: Source-Pathway-Receptor model for Butts Field

3.3.3 Knockhatch Stream priority areas This priority area (shown in Figure 3-13) covers the area draining to the Knockhatch Stream extension, locally known as Diplocks Stream.

Figure 3-13: Knockhatch Stream priority area The Knockhatch Stream extension is classified as main river throughout this priority area. On a site visit it was observed that the watercourse had recently been cleared and water could flow undisrupted. The flood history records indicate that the common sources of flooding include foul sewer flooding due to hydraulic overload and groundwater flooding. There are also a number of flood incidents where the source was not recorded. The groundwater flood risk map does not show this area to be at risk of groundwater flooding. However, the flood history states that flooding has occurred due to groundwater on two occasions. Sewer flooding has occurred at two locations within the hotspot. Southern Water attribute the cause to hydraulic overload. It is not clear whether unplanned flows are accessing the sewer network via surface water inundation of manhole covers or groundwater infiltration; both surface water and groundwater flood incidents have been reported in the immediate area. Consequently it is recommended that this area is monitored closely in order to better understand the underlying mechanisms. There were no reports of flooding following storms in January 2015.

The uFMfSW shows that there is significant flood risk to properties north of the Diplocks Stream, in a 1 in 1000 year return period. The flood zones show the fluvial flood risk is predominately to the south of the watercourse, which could impact the Diplocks industrial estate. The Knockhatch Stream is the lowest priority area identified in Hailsham as its designation is driven from flood risk rather than flood history. However, it is important that this watercourse remains maintained by the Environment Agency. This enhanced conveyance is an appropriate measure to mitigate the fluvial risk to the Diplocks.

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 planning authority within Wealden District Council so strategic planning decisions can be made in conjunction with flood risk. It should be noted that areas identified for development could be subject to change as the planning process progresses.

4.1 Local Development Framework Wealden District Council confirmed plans for Strategic Development Areas (SDAs) in 20144. This document identified sites for development and dates of key milestones. Areas within Hailsham and Hellingly identified for development are displayed in Figure 4-1.

Figure 4-1: Strategic Development Areas identified in Hailsham and Hellingly.

4 Wealden District Council (2014) Strategic Sites Local Plan

Table 4-1 lists all the Strategic Development Areas (SDAs) identified in Hailsham and Hellingly and the planned land use and programmed commencement date.

SDA Purpose Location Commencement Redevelopment - Land in the east of Hailsham, Magham None specified SDA2a Urban extension Road. Urban extension – None specified Land in the east of Hailsham at and to SDA2b residential the rear of Lynton. provision Urban extension – None specified Land in the east of Hailsham, SDA2c residential Amberstone. provision Urban extension – None specified Land in the north of the study area, off SDA3a & b residential New Road, Hellingly. provision Table 4-1 Strategic Development Areas in Hailsham and Hellingly

4.2 Development areas in flood hotspots The National Planning Policy Framework (2012) reinforced the concept that local planning authorities should take a strategic approach to development by creating a Local Plan, supported by a Strategic Flood Risk Assessment5 (SFRA). The Wealden District SFRA Levels 1 & 2 cover Hailsham and Hellingly. In the north east of Hailsham, five areas have been identified for development; SDA2a, SDA2b, SDA2c, SDA3a and SDA3b. These fall within the Harebeating Stream flood hotspot. The development progress for each site varies. Where development is in the early stages of the planning process, there is an opportunity to encourage flood resilient building techniques and adopting appropriate measures to managing surface water. It is also worth noting that the Internal Drainage Board (IDB) would have an interest in any development in the area as it is within the Pevensey Levels Internal Drainage District. Much of the allocated land for development is currently greenfield. However, the uFMfSW shows an existing surface water flood risk to SDA2c, SDA3a and SDA3b. Urbanisation of these areas could increase the risk due to an increase in impermeable area. Therefore, it is important to maintain greenfield runoff rates to manage the existing surface water flood risk and prevent flooding in communities downstream. The uFMfSW shows that areas of SDA2c, SDA3a and SDA3b are at risk from surface water flooding. By increasing the impermeable area It should be noted a Flood Risk Assessment (FRA) is a statuary requirement for any planning application of an area greater than one hectare. Therefore, the effect of flood risk should be assessed prior to development, noting the likelihood of there being two streams draining into Harebeating stream, as opposed to only one as indicated on the Environment Agency’s DRN map.

4.3 Planning policy For Hailsham, planned development is focused in the Harebeating Stream hotspot. This area has been identified as being of significant local flood. Therefore, it is recommended that local authority planners are made aware of the drainage issues in this location for communication to developers.

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

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 Hailsham and Hellingly. 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 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

Generic action plan Outline broad scale actions Study area wide applicable across the study (Section 5.3) area Recommend strategic actions Specific streets with priority Priority area action plan to manage the flood risk in areas (Section 5.4) priority areas Propose specific activities in Specific points where flooding Incident specific action plan response to a reported flood has been reported (Section 5.5) 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 Hailsham and Hellingly. Actions to mitigate these issues fall under four themes and are listed in the Generic Action Plan below.

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 strategic growth planned in Hailsham and Hellingly is currently focused on the priority area of Harebeating Stream. It is recommended that the planning authority incorporate the findings and thereby raise issues to developers through its local plan.

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 Hailsham. In particular, it is recommended that Station Road be considered for an enhanced cleansing regime due to its flood history.

5.3.4 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 Hailsham and Hellingly 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, retain surface water or filter pollutants and some SuDS techniques are multipurpose. Together, the sequence of SuDS components forms a SuDS management train. SuDS components fall into three general categories; source control, retention and infiltration. On the 10th 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 As discussed in Section 1.5 Hailsham and Hellingly is in the headwaters of the Cuckmere catchment. Any runoff generated in Hailsham and Hellingly will impact communities downstream. As a result, source control is an important SuDS component in Hailsham and Hellingly as the benefits will be felt both within the town and by communities downstream. Measures of source control include permeable paving, green roofs and rainwater harvesting. In Hailsham, the topography is relatively flat, with large areas showing little variation in elevation. Permeable paving may be feasible as the low gradient allows for low velocity runoff to permeate into a subsurface as opposed to continuing overland. However, the suitability of infiltration SuDS should be considered on a case by case basis due to the variability of permeability within the Wealden Group geology. Green roofs and rainwater harvesting could also be highly effective 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 groups6. 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 retentions 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 improve both flooding from surface water and fluvial flooding. However, retention SuDS devices require space and suitable land is scarce in Hailsham. As a result, retrofitting retention devices is often impractical. Strategic development areas have been identified in Hailsham as these present an opportunity to incorporate retention SuDS at planning stage - as was included at the Harold Avenue development.

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 Hailsham and Hellingly is the Weald Clay formation which is part of the Wealden Group. The Weald Clay formation in the area comprises of bedded mudstones and mudstones with intermittent siltstone, sandstones, limestones and clay ironstones. The bedrock geology is however overlain in areas in the north (River terrace

6 Southern Water (2013) Available at - http://www.yourwatermeter.com/waterbutt

deposits of sand and gravel) and south and east (Alluvium) which may hinder or aid infiltration dependent upon their spatially variable permeability. The bedrock porosity is also variable associated with rock type; an increase in clast size (sandstone) and would likely permit greater infiltration for example. Therefore, it is likely, in some areas of Hailsham and Hellingly that infiltration SuDS could be a viable option.

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

5.4.1 Harebeating Stream A high priority action is the survey of this culverted watercourse to establish the route, condition and capacity of the culvert. This step is fundamental to understanding the culvert capacity, to inform if the culvert has capacity to receive additional flows, or if indeed the culvert is likely to surcharge causing fluvial flooding. To provide a complete understanding of flooding within the Harebeating Stream catchment, further investigations to clarify/ascertain the local conditions for the Harebeating Stream catchment is required. This study could include modelling of all the flood mechanisms operating in the catchment - fluvial, surface water and sewer. The hydraulic modelling would increase understanding of the flood mechanisms operating in the Harebeating Stream catchment. In addition, it would form a baseline against which options can be fully appraised. Action Purpose Action Owner CCTV of the culverted Ascertain asset location, ESCC, WDC and watercourses within this priority condition, connections and ESCC highways area capacity Understand all flood Undertake a detailed SWMP mechanisms and test flood ESCC mitigation options

Table 5-2: Summary of actions on Harebeating Stream

Woodlands Close sub area Following the survey proposed across the Harebeating Stream priority area, options can be explored to determine the suitability to utilise the culvert to manage surface water flooding. For example, it is recommended that the feasibility of installing a gully in the alley and connecting to the culvert at the footpath between Woodlands Close and Oak Tree Way be investigated as illustrated in Figure 5-1.

Figure 5-1: Action locations on Woodlands Close A secondary flow route has been observed from Battle Road towards Woodlands Close. It is not currently understood what the mechanism is here, although speculation connects it to the infill of drainage ditches. It is recommended that this is investigated as part of a detailed SWMP. Action Purpose Action Owner Gulley inlet Remove surface water ESCC Highways

Table 5-3: Action summary for Woodlands Close

Harebeating Drive sub area Local residents are managing the surface water flood risk with a tarmac bund separating their driveways from the highway. If the road was to be resurfaced, this bund could be lost which would allow shallow surface water to flow towards people's homes. Therefore, it is recommended that the flood bund be reinstated if resurfacing works are undertaken. Following the proposed investigation across the Harebeating Stream priority area, options can be explored to determine the suitability to utilise the culvert to manage surface water flooding. For example, it is recommended that daylighting the culvert watercourse behind properties on Harebeating Drive is investigated. The location of these actions is indicated in Figure 5-2 below.

Figure 5-2: Action map for Harebeating Drive The actions recommended on Harebeating Drive and Harebeating Crescent have been summarised in Table 5-4. Action Purpose Action Owner Reinstate driveway road humps Maintain current flood defence ESCC Highways following resurfacing ESCC, WDC and land Daylight watercourse Provide upstream attenuation owners

Table 5-4: Action summary for Harebeating Drive

Harold Avenue sub area The flood incident at Harold Avenue highlights the importance of considering all sources of flooding during a Flood Risk Assessment (FRA) conducted as part of a planning application. Where an FRA concludes there is a risk of flooding, flood resilience measures should be a condition of development. For example, finished floor levels should be set above road level to protect against shallow overland flow. In addition, ‘Smart Air Bricks’ should be adopted to prevent flood water accessing properties via air bricks. Two actions have been proposed to specifically to manage the flood risk to Harold Avenue. It is recommended a field drain is excavated behind the properties to store and convey surface water runoff away from the properties and the residences are fitted with Property Level Protection (PLP) to increase their resilience. The location of these actions is summarised in Figure 5-3.

Figure 5-3: Action locations on Harold Avenue The actions recommended for Harold Avenue are summarised in Table 5-5. Action Purpose Action Owner Convey field runoff away from Excavate a drainage ditch Developer residential receptors Assess all sources of flooding during FRAs. Recommend the Designing flood resilient WDC and ESCC use of flood resilience measures buildings in at risk areas.

Table 5-5: Action summary for Harold Avenue

5.4.2 Horse Eye Sewer priority area Horse Eye Sewer has a history of flooding; particularly from watercourses and pluvial runoff. These flood incidents predominately relate to asset condition with assets not working to capacity due to blockage. This highlights the Horse Eye Sewer catchment as particularly sensitive to asset condition. As a result, it is recommended that prioritised maintenance is planned for the Horse Eye Sewer.

Butts Field sub area The fluvial flooding has been recorded at Butts Field and is all attributed to blockage. The blockages are as a result of fly tipping blinding a culvert. This is not an integrated flood mechanism so it has been addressed in the site specific action plan. Action reference FOW09 and FOW12 are both recommend that Wealden District Council monitor fly tipping at this location and that evidence is collected to support prosecution. This action has been flagged as high priority.

Station Road sub area The surface water flooding reported on Station Road has been attributed to pluvial runoff and hydraulic overload. As the flooding reported has largely only impacted highways, the mitigation measures are less high priority here. However, it is recommended that flooding here is monitored by ESCC to understand the cause of flooding here, as stated in SWPR33 in the site specific action plan.

5.4.3 Knockhatch Stream The fluvial flooding reported on Knockhatch Stream was as a result of blockage. Under the Environment Agency’s current maintenance regime there have been no further incidents of fluvial flooding reported. Therefore, continuing the current maintenance regime is recommended in action FOW04 of the site specific action plan. The conditions leading to foul water flooding or surface water flooding are not currently understood here. Therefore, it is recommended that if future instance of flooding occur, these are investigated to understand why flooding occurred.

5.4.4 Other areas In the majority of cases, flood incidents in locations outside of flood prone areas have been dealt with in the site specific action plan. However, the high priority action for Stroma Gardens has been explained in more detail below.

Stroma Gardens sub area Stroma Gardens is in the north west of Hailsham. A communal parking area was flooded in January 2015. It is believed that this flooding was due to the blockage of a culvert. An onsite investigation identified a culvert under a private driveway that appeared totally blocked. It is recommended that Wealden District Council investigate the extent of this blockage and identify possible solutions.

5.5 Incident specific actions A suitable action has also been set for every flood incident on the Hailsham and Hellingly 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 affective 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 old records and low vulnerability receptors. The completed actions had 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 identified priority area which is an area where repeated flood incidents have been recorded together with high predicted flood risk. For the Hailsham and Hellingly SWMP, further detailed assessment is recommended on Harebeating Stream. 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.

Appendices A Appendix - Data Quality Scores

B Appendix - Flood History Table

C Appendix - Quantifying Surface Water Flood Risk

Table C-1: Receptors considered as critical infrastructure Group name Sub-class Ambulance Station AMBULANCE STATION ADULT EDUCATION EDUCATION FIRST SCHOOL FURTHER EDUCATION FURTHER EDUCATION COLLEGE HIGH SCHOOL HIGHER EDUCATION INFANT SCHOOL JUNIOR SCHOOL MIDDLE SCHOOL Education NURSERY PRIMARY SCHOOL PRIVATE PRIMARY SCHOOL SCHOOL SCHOOL FOR THE DEAF SECONDARY SCHOOL SPECIAL SCHOOL TECHNICAL COLLEGE UNIVERSITY PRE SCHOOL EDUCATION ELECTRICITY GENERATING Electricity ELECTRICITY SUB STATION Fire Station FIRE STATION GAS DISTRIBUTION GAS MONITORING Gas GAS PRODUCTION AND DISTRIBUTION GAS REGULATING GAS STORAGE DAY CARE HOSPICE HOSPITAL MENTAL HEALTH CENTRE NATIONAL HEALTH SERVICE WALK IN Health CENTRE NURSING HOME MEDICAL SERVICES MORTUARY SURGERY POLICE HEADQUARTERS Police POLICE STATION POLICE SERVICES SEWAGEFILTRATION SEWAGEOUTFALL SEWAGEPUMP HOUSE Waste Water SEWAGEPUMPING SEWAGERECYCLING SEWAGESTORAGE SEWAGETREATMENT WATER TREATMENT Water Treatment PUMP HOUSE HM COASTGUARD RESCUE Coastguard HM COASTGUARD SERVICES RETIREMENT HOME Socially vulnerable REST HOME RESETTLEMENT CENTRE

Group name Sub-class HM DETENTION CENTRE HM PRISON HM YOUNG OFFENDERS INSTITUTION CHILD DAY CARE CHILDRENS HOME CHILDRENS NURSERY

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 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 Hailsham and Hellingly is shown in Figure D-1.

Figure D-1: The GeoPDF flood risk and recorded flooding incidents in Hailsham and Hellingly. 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.1.1 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.

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 Hailsham and Hellingly 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.1.2 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.1.3 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 Strategic Development Area (SDA) reference number. Finally a study boundary delineating the areas of interest has been marked.

E Appendix - Incident Specific Action Plan

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