Strategic Flood Risk Assessment Level 1. Volume II Stockton on Tees SFRA Technical Report. June 2010 FINAL REPORT

Transcription

1 Strategic Flood Risk Assessment Level 1 Volume II Stockton on Tees SFRA Technical Report June 2010 FINAL REPORT JBA Consulting The Brew House Wilderspool Park Greenhall's Avenue WARRINGTON WA4 6HL UK t: +44 (0) f: +44 (0) www@jbaconsulting.co.uk Client Address: Stockton-on-Tees Borough Council PO Box 11, Church Road, Stockton-on-Tees TS18 1LD

2 !"#!$ %&' ( Draft Report (v.1.0) Digital Copy (as a pdf) to Matthew Clifford and Cameron Sked Final Report (v.2.0) June 2010 Updated after SBC and EA comments Matthew Clifford!" This report describes work commissioned by Stockton-on-Tees Borough Council under Order PD Stockton-on-Tees Borough Council s representative for the contract was Matthew Clifford. Sam Wingfield of JBA Consulting carried out the work. Prepared by: Sam Wingfield, BSc MRes Analyst Reviewed by: Kevin Keating, BEng MSc(Eng) MICE CEng Technical Director Approved by: Kevin Keating )*)! This document has been prepared solely as a Final Report for Stockton-on-Tees Borough 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.

3 +"!, (-. " JBA would like to thank all those who provided information and data for this report. From Stocktonon-Tees Borough Council: Matthew Clifford. From the Environment Agency: Gemma Alecks.

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5 / * *..$ Stockton-on-Tees Level 1 SFRA This report has been produced as a Level 1 Strategic Flood Risk Assessment (SFRA) for Stocktonon-Tees Borough Council, in accordance with PPS25 and its Practice Guide. Development & Flood Risk Local Planning Authorities (LPAs) have a raft of issues to consider when planning future development. These are dictated by Government Planning Policy Statements. Planning Policy Statement 25 (PPS25) relates to development and the constraint of flood risk, with its overarching aim of avoiding development in flood risk areas. This is achieved through PPS25 by the sequential approach to land allocation, meaning that development should be firstly avoided in flood risk areas wherever possible before considering the vulnerability of development planned or possible mitigation measures. The sequential approach is governed by two tests; the Sequential and Exceptions Test. The consideration of flood risk to people and development must be considered by the LPA at the earliest stage of spatial planning decisions and these tests allows this process to be transparent and affective. In order to carry out these tests a coherent understanding of flood risk is needed at a local level. High level policy and guidance documents such as Catchment Flood Management Plans (CFMPs), Shoreline Management Plans (SMPs) and Regional Flood Risk Appraisals (RFRA) have provided a good introduction in to flood risk; however they do not provide the level of detail required for the LPA to make the right spatial planning decisions. Strategic Flood Risk Assessments (SFRAs) offer this local level of understanding. SFRAs provide the LPA with a central source of all relevant flood risk information and the evidence base to make tough planning decisions and develop focused local policies required to inform the Local Development Framework (LDF). The SFRA therefore becomes a key planning tool that enables the LPA to select and develop sustainable site allocations. A Level 1 SFRA offers the foundation of this evidence base. It is based purely on the collation of existing flood risk information. The Environment Agency Flood Map is the main source of fluvial and tidal flood information across England and Wales and is the basis of PPS25 Flood Zones used in the Sequential and Exception Tests. The Level 1 SFRA must also consider flooding from all other sources (surface water, sewers, groundwater and artificial sources). This is only achievable through consulting with those stakeholders with specific interest or knowledge in other sources of flooding. The Level 1 SFRA is assisted greatly by the use of Strategic Flood Risk Maps providing information on flood risk factors needed to be taken into account. The PPS25 Flood Zone Map enables the LPA to carry out the first sweep of Sequential Testing. The additional maps produced as part of the Level 1 SFRA should be used during the Sequential Test sieving process further identify inappropriate development. Once the LPA has carried out the Sequential Test sieving process, they still may wish to allocate vulnerable development in high risk areas due to the wider need for economic growth and regeneration. In this case the allocations must pass the Exception Test. The evidence provided in the Level 1 SFRA is not detailed enough to justify development through the Exception Test. In order to achieve this Level 2 SFRA must be carried out. A Level 2 SFRA provides the LPA with a detailed understanding of flood hazard, assessing flood depth, velocity and residual risks such as flood defence breaching or overtopping. This information provided in the Level 2 SFRA will give the LPA a much more detailed understanding of flood risk at (

6 potential development sites. Although it will not provide all the information needed to apply the Exception Test, it will include the appropriateness of the development and the likelihood of it remaining safe if flooded. If the LPA has justified the development by passing parts a) and b) of the Exception Test, it must be supported by a site specific Flood Risk Assessment (FRA) in order to pass part c). The Three Level 1 SFRA Volumes The Level 1 SFRA is presented in three volumes, each with their own purpose and intended audience. VOLUME I: Understanding the SFRA Process Volume I of the Stockton-on-Tees SFRA introduces the SFRA process. It is an excellent reference document for current flood risk management drivers, national regional and local planning policy and introduced Environment Agency policy such as the Tees CFMPs and SMPs. The report also provides a brief understanding of the mechanisms of flooding and flood risk for those new to the subject. More importantly, it provides a comprehensive discussion on PPS25, the Sequential, Exception Test and links regional and local flood risk assessments. Volume I holds the main Consultation & Data Management section, identifying key stakeholders and their involvement in the SFRA process. This Volume should be read by: The general public or those new to flood risk Those wanting to understanding current flood risk management drivers Those wanting to understand the sequential approach to flood risk management And generally by those involved in Development Control, Planners and Developers wanting to understand the wider constraints of developing in flood risk areas. VOLUME II: SFRA Technical Report Following on from the Consultation & Data Management section in Volume I, Volume II provides the technical information and methods used in the assessment of flood risk across Stockton-on- Tees. It assesses six sources of flooding including; fluvial, tidal, surface water, sewers, groundwater and reservoirs and other artificial sources. The Volume also introduces the Environment Agency Flood Warning System and residual risks associated with flood defences. As discussed, flood risk has many dimensions and as a result has been presented through a suite of maps. These extend the level of detail in the Environment Agency Flood Zone maps. The SFRA maps include: SET A: SET B: SET C: SET D: SET E: PPS25 Flood Zones Flood Zone 3 Depths Tidal Climate Change Sensitivity Flood Risk Management Measures Areas Naturally Vulnerable to Surface Water Flooding Volume II along with the suite of SFRA maps, should provide the evidence base of the Stocktonon-Tees Level 1 SFRA. It has been arranged in one volume to allow technical information to be easily updated when reviewed. It is only this Volume that can be updated with new flood risk information when available. Volume I and III would be difficult to update without completely revisiting the SFRA process. (

7 Section 4 provides the results of the first pass of the Sequential Test against Stockton-on-Tees Council s proposed development allocations. This Volume should be read by: Spatial Planners Development Control Planners Developers Emergency Planners Key Stakeholders including the Environment Agency and Northumbrian Water VOLUME III: SFRA Guidance for Spatial & Development Management Volume III of the Stockton-on-Tees SFRA provides guidance and recommendations to spatial planners, planners, developers and emergency planners, how to use the flood risk information provided in Volume II and further plans which are required to improve the understanding of flood risk in Stockton-on-Tees. Initially the Volume discusses further work required such as Level 2 SFRAs and SWMPs which has been informed by the findings of Volume II. This extra work will provide Stockton-on-Tees Council with a strategic and coherent framework for managing flood risk in their area. This Volume should be read by: Spatial Planners Development Control Planners Developers Emergency Planners Key Stakeholders including the Environment Agency and Northumbrian Water (

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9 !" " REVISION HISTORY CONTRACT PURPOSE ACKNOWLEDGEMENTS EXECUTIVE SUMMARY CONTENTS Page i i i i iii iv (!* 1.1 Flood Zone Map,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1.2 Flood Defences,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1.3 Flood Risk Management and Hydraulic Modelling Studies,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1.4 Topographic Data,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 1.5 Historical Flooding,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 0 2 4!!( +" #!!*-#!! +!" Introduction,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. 2.2 Tidal Flood Risk,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. 2.3 Fluvial Flood Risk,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2.4 Flooding from Land,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,/ 2.5 Flooding from Sewers,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2.6 Flooding from Groundwater,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0 2.7 Flooding from Reservoirs & other Artificial Sources,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0 2.8 Effects of Climate Change,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,0 2.9 Geology & Soils,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2.10 Flood Defences,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 2.11 Flood Warning Areas,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. -!!( +. ))" Introduction,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 3.2 PPS25 Flood Zones Maps,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 3.3 Flood Zone 3 Depth Map,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Climate Change Sensitivity Maps,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1/ 3.5 Flood Risk Management Measures Maps,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1/ 3.6 Areas Vulnerable to Surface Water Flooding Maps,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 )!!" Introduction,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 4.2 Current Development Site Sequential Test,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Flood risk and the SFRA 2009 allocations,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Individual Planning Applications,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,// APPENDICES: APPENDIX A: - FIGURES (

10 APPENDIX B: - SEQUENTIAL TEST TABLE 2

11 !-* Figure 1-1: LiDAR Coverage in Stockton BC,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Figure 2-1: Flooding at Port Clarence in 1953,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Figure 2-2: Potential CDA in Billingham,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Figure 2-3: North Tees proposed development area and SWM,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Figure 3-1: Tidal graphs for modelling sea level in the Tees Estuary,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 Figure 4-1: Screenshot of Sequential Test Spreadsheet,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 Figure 4-2: Bowesfield Riverside sites with Flood Zone 3a, 3b and the raised defences,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1 Figure 4-3: Teesdale 2 development allocation and the historic flood outline,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,/ Figure 4-4: Tees Marshalling Yard allocation with Flood Zones and historic flooding locations,,,,,,,,,,,,,,,,,,,,,,,,,,,,/ Figure 4-5: Surface Water Map at Tees Marshalling Yard Site,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,/1! Table 1-1: DEM availability,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Table 2-1: Extreme tidal level estimates for the Tees Estuary,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Table 2-2: Effect of sea level rise on water levels in the Tees Estuary,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,. Table 3-1: Functional Floodplain (Flood Zone 3b and Candidate 3b) Mapping,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,11 Table 4-1: Summary of Development Sites at Risk of Fluvial & Tidal Flooding,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,10 Table 4-2: Summary of Development Sites at Risk of Surface Water Flooding,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1. Table 4-3: Large sites with high surface water flooding coverage,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,// 2

12 !" ABD A.P. CFMP CLG COW CS DPDs EA EU FAS FEH FCERM FRA FRM IDB IDD IFM LDDs LDF LPAs NEA NFCDD NPD NWL PPG PPS RBD RBMP RFRA RPB RPG RSS RVFD SA SEA SFRA SFVI SMP SoP SPD SUDS SWMP UDP WCS Areas Benefiting from Defences Annual Probability Catchment Flood Management Plans Communities and Local Government Critical Ordinary Watercourse Core Strategy Development Plan Documents Environment Agency European Union Flood Alleviation Schemes Flood Estimation Handbook Flood and Coastal Erosion Risk Management Flood Risk Assessment Flood Risk Management Internal Drainage Board Internal Drainage District Indicative Floodplain Map Local Development Documents Local Development Framework Local Planning Authorities North East Assemble National Fluvial and Coastal Defence Database National Property Dataset Northumbrian Water Ltd Planning Policy Guidance Planning Policy Statement River Basin District River Basin Management Plan Regional Flood Risk Assessment Regional Planning Bodies Regional Planning Guidance Regional Spatial Strategy Receptors Vulnerable to Flooding Database Sustainability Appraisal Strategic Environmental Assessment Strategic Flood Risk Assessment Social Flood Vulnerability Index Shoreline Management Plans Standard of Protection Supplementary Planning Document Sustainable (Urban) Drainage Systems Surface Water Management Plan Unitary Development Plan Water Cycle Study 2

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17 (!* 1.1 Flood Zone Map The Environment Agency Flood Zone Maps provide an overview of areas considered susceptible to flood risk in the study area as a result of fluvial and tidal flooding. These maps have been prepared in a consistent manner across England and Wales and provide an estimation of the extent of flooding for both the 1 in 100 and 1in 1000 year annual events. The Flood Zone maps were prepared using a methodology based on the national digital terrain model (NextMap), derived river flows (Flood Estimation Handbook (FEH)) and two dimensional flood routing. The derived Flood Zone extents have been adjusted in some locations where the results are inconsistent with historical flooding extents, where more detailed flood mapping studies have been completed, or where there are known errors in the digital terrain model used. In Stockton Borough Council, the majority of fluvial and tidal Flood Zones have already been updated with the results of detailed flood mapping studies (see Section 1.3). The Environment Agency Flood Zone Maps are precautionary in that they do not take account of flood defences and, therefore, represent a worst-case extent of flooding. They do not consider other forms of flooding and do not take account of climate change. PPS25 divides the country into three basic flood zones, Flood Zones 1, 2 and 3, corresponding to areas of low, medium and high flood risk, respectively Delineation of Low Risk Zone 1 PPS25 considers areas within Flood Zone 1 to be at low risk to flooding. The probability of flooding within this zone is less than 1 in 1000 or can be easily defined as areas within the Borough Council area located outside either Flood Zone 2 or Delineation of Medium Risk Zone 2 PPS25 considers areas within Flood Zone 2 to be at medium risk of flooding. The probability of fluvial flooding within this zone is between 1 in 1000 and 1 in 100 (or between 1 in 200 and 1 in 1000 for tidal flooding). In general, Flood Zone 2 is considered suitable for most development except highly vulnerable land uses where the Exception Test is required, such as police stations, fire stations and ambulance stations Delineation of High Risk Zone 3 PPS25 considers areas within Flood Zone 3 to be at high risk of flooding. PPS25 splits Flood Zone 3 into two sub-zones, 3a and 3b, which correspond to high probability flooding and the functional floodplain. Flood Zone 3a: High Probability o In accordance with Table D.1 of PPS25 This zone comprises land assessed as having between a 1in 100 and 1 in 1000 annual probability of flooding or between a 1 in 200 and 1 in 1000 year annual probability of sea flooding in any year. Flood Zone 3b: The Functional Floodplain o In accordance with Table D.1 of PPS25 This zone comprises land where water has to flow or be stored in times of flood

18 1.1.4 Delineation of the Functional Floodplain SFRAs are tasked with the responsibility of defining Flood Zone 3b. PPS25 suggests the 1 in 20 year flood event for the baseline of a functional floodplain, however, a more or less extreme event can be used where appropriate, depending on catchment characteristics and on agreement between the LPA and the Environment Agency. SFRAs can also identify where it might be appropriate to extend the 1 in 20 year flood outline to areas within Flood Zone 2 and 3 to restore or expand the functional floodplain. The ability to identify and safeguard large enough areas against redevelopment and development in both urban and rural areas, means that existing open space can potentially be used for flood storage, effectively reducing flood risk downstream. This process assists Flood Zone 3 policy aims, identified in table D.1 in PPS25, which include: a) Reduce the overall level of flood risk in the area through the layout and form or the development and the appropriate application of sustainable drainage systems, b) Create space for flooding to occur by restoring functional floodplain and flood flow pathways and by identifying, allocation and safeguarding open space for flood storage. The SFRA should be fully integrated with CFMPs and other strategies that show, at catchment scale, the need to protect the floodplain and avoid inappropriate development in high flood risk areas. 1.2 Flood Defences As discussed above the Environment Agency Flood Zone maps do not take account of the presence of flood defences (although defended areas and the location of raised defences are included in the suite of information provided with the maps). PPS25 1 states that defended areas (i.e. those areas that are protected to some degree against flooding by the presence of a formalised flood defence) are still at risk of flooding, and therefore sites within these areas must be assessed with respect to the adequacy of the defences. The Environment Agency s National Flooding and Coastal Defence Database (NFCDD) has been supplied and provides information existing defences in the area, as well as categorising them by type and providing information on who owns and maintains them. Areas Benefiting from Defences (ABDs) have also been provided. ABDs are those areas which benefit from formal flood defences in the event of flooding from rivers with a 1 in 100 year event or from the sea with a 1 in 200 year event. If the defences were not there, these areas would be subject to increased flood risk. 1.3 Flood Risk Management and Hydraulic Modelling Studies Many of the main rivers throughout Stockton-on-Tees have been represented using detailed hydraulic models and the Flood Zones in these locations give a good representation of reality. However, there is no single comprehensive hydraulic model for each of the river systems within the Borough. Flood Zones outside of the modelled reaches are still represented with broad scale modelling techniques used in the original Flood Zone map definition and are therefore more prone to error. The hydraulic models available in the area include: 1. Draft Tees Tidal Flood Management Strategy February This includes a 1D **&%'&E( *=>!"# "2E$& &E,

19 1.3.1 Tees CFMP Hydrodynamic ISIS Model of the fluvial Tees ((Environment Agency). 2. North East Regional Flood Risk Appraisal - January A 2D TUFLOW model of the Tees Estuary was produced by JBA Consulting for this project. This model had not been fully developed but was used for a comparison with the Flood Zone maps. 3. Tees Valley SFRA - February Within this project, 2D JFLOW models were produced to assess defence breaching and overtopping (JBA). 4. Lustrum Beck Flood Alleviation Study This includes a 1D Hydrodynamic ISIS Model (Environment Agency). 5. Unnamed watercourse in Stockton-on-Tees September Part of the Dales Area Floodplain Mapping Phase 2 Studies and includes a HEC-RAS hydraulic model (Environment Agency). 6. Cowbridge Beck Backwater model developed in 2006 (Environment Agency). The Tees CFMP will be used for evidence of flood history, flood risk locations and sources. This information will be of a broad scale nature so will need to be supplemented with other detailed information. The proposed flood risk management policy for different areas within the Borough will be noted in order to help assess if future development proposals are likely to be sustainable. Between June 2007 and January 2008 JBA Consulting undertook strategic catchment modelling work for the Environment Agency, primarily for the Environment Agency s CFMPs in the North East (including the Tees CFMP). The modelling generated 19 new Flood Maps for approximately 10,000 km of watercourse, representing different flood events and assumptions about flood risk management measures. This catchment modelling was also developed in order to update the parts of the Environment Agency s Flood Map for Flood Zone 3 where no detailed river modelling studies had been completed. This catchment modelling incorporates a number of improvements over the original Flood Maps, including the use of new LiDAR data in place of SAR (NextMap-Britain) data, where available. A number of different scenarios were modelled to represent when flood water would come out of bank e.g. for the 1 in 2 year event. Included in these outputs are flood depth and flood hazard maps. The current Flood Zone maps have not been updated with this new information and it is not known whether they will be updated in the future. It was initially thought that the SFRA could use the outputs to represent Flood Zone 3b, a climate change flood outline, flood depth and flood hazard maps (where there is no detailed modelling). However, it has not been possible to find a scenario that aligns with the current Environment Agency Flood Zone maps. Flood Zone 3b would be greater than Flood Zone 3a in places for example. The SFRA will use a flood depth map for a broad scale overview of the potential flood depths in Stockton BC. The Environment Agency have stated that it is critical for the functional floodplain outline to be as accurate as possible and that more minor (non-main) watercourses should be excluded unless modelled outlines are available Draft Tees Tidal Flood Management Strategy The Environment Agency has produced a draft flood risk management strategy for the Tees Estuary (Draft Tees Tidal Flood Risk Management Strategy dated February 2008). The aim of this study is to determine a sustainable plan for managing flood risk within the Tidal Tees Estuary for the next 100 years. The first stage of the plan will be to identify the key risks and measures to manage them along with further studies to build on our understanding. This draft study will be used to obtain the extreme tide levels for the Tees Estuary. This includes estuarine water levels allowing for predicted sea level rise. The Tees Tidal 1

20 Strategy will also be used to gain a better understanding of the Tees Estuary and the flood risk it poses to the Borough. The proposed flood risk management options will also be considered and how this may affect future development North East Regional Flood Risk Appraisal A scoping study for the North East Regional Flood Risk Appraisal (NE RFRA) was completed by JBA Consulting in January The primary objective of the NE RFRA is to provide an appraisal of strategically significant flood risk issues and guide strategic planning decisions. The findings of this work will form part of the Regional Spatial Strategy evidence base. A 2D TUFLOW model of the Tees Estuary was produced by JBA Consulting for the NE RFRA to show that the Flood Zone maps needs to be improved on the Tees Estuary. The TUFLOW model was used to create an undefended tidal climate change outline for the area. A depth grid is available as a modelled output. This model will be used to represent tidal flood risk to the Borough from the Tees Estuary. This is not an Environment Agency model and therefore the outlines used will not necessarily be recognised by the Environment Agency as the equivalent of Flood Zone maps. However, they will provide a more accurate definition of tidal flooding from the Tees Estuary. Therefore, this model will be used in the Level 2 SFRA Tees Valley SFRA 2007 An SFRA was completed for the Tees Valley local authorities in This SFRA was a good example of an SFRA produced prior to the publication of the PPS25 Practice Guide, but it needs updating to reflect the new guidance. The majority of the flood mapping that was used in the 2007 SFRA has now been updated. However, the following depth and breach assessments completed by JBA Consulting as part of this earlier SFRA may still be of use in this SFRA update: J ' *&3 &@3( $$& &B & J *&3 &@3 && 6$ =&$3!" 67* $%%$ %> J ' *&3 &@3 &&"7%! & The 2007 SFRA will also be used for additional flood history and flood risk location information Lustrum Beck Flood Alleviation Study A project appraisal report (PAR) for a flood alleviation scheme (FAS) has been produced for Lustrum Beck by the Environment Agency. The scheme has been designed to protect over 200 properties in Stockton in the Lustrum Beck catchment and received Environment Agency funding approval in November 2003 with Planning Approval from Stockton Borough Council in April The Lustrum Beck FAS proposal consists of flood storage in the upper catchment at Hartburn, with local defences at Oxbridge, Newtown and the Tilery. Flood defences have been constructed in Hartburn and defences are planned as part of the proposed Tilery development. However it is now uncertain whether the remainder of the scheme, in particular the storage element, will get future funding. The project included the development of an ISIS hydraulic model of the Beck. The modelling outputs will be used to define Flood Zone 3b (where appropriate) and to show the likely flood extent resulting from increased rainfall intensity caused by climate change. Any flood depth and hazard maps will be utilised during the proposed Level 2 SFRA. Flood history and the description of flood risk will also be used to inform the SFRA. /

21 1.3.6 Stockton Unnamed Watercourse Floodplain Mapping Study This is a detailed study of two unnamed tributaries in Stockton-on-Tees and was completed in 2005 by JBA for the Environment Agency. The first tributary off Eastbourne Road and the second is off Swinburn Road. The modelling was commissioned as part of the Environment Agency s Phase 2 Flood Risk Mapping Programme in order to improve information on flood risk and provide flood risk maps of the watercourses for planning and operational purposes. The study included construction of a HEC-RAS hydraulic model and simulation of design events in order to produce water level estimations at key locations. The floodplain was modelled using information derived from LiDAR data. The flood outlines produced for this study will be used to define Flood Zone 3b (where appropriate), a climate change flood extent and provide a more accurate Flood Zone Cowbridge Beck A flood mapping study was completed by JBA Consulting in 2006 for Cowbridge Beck. The detailed study of Cowbridge Beck was produced for the Environment Agency s Flood Risk Mapping programme. It follows a phase 1 study carried out by Atkins in Cowbridge Beck was identified as a critical ordinary watercourse and became a main river in April A steady state HEC-RAS hydraulic model of Cowbridge Beck was constructed for this study. The flood outlines produced from this study will be used to produce functional floodplain and climate change flood extents where appropriate. 1.4 Topographic Data The essential dataset required for flood modelling, mapping and general elevation information is a Digital Elevation Model (DEM). There are two main sources of DEM data for the Borough, as shown in &7. Table 1-1: DEM availability ( <8! > ( > Nextmap SAR Environment Agency 5m Filtered - LiDAR Environment Agency 2m Filtered & unfiltered 2000 to 2005 LiDAR Environment Agency 1m Filtered & unfiltered 2008 to 2009 LiDAR Environment Agency 0.5m Filtered & unfiltered 2006 LiDAR will be used in preference to Nextmap SAR data as it has a higher vertical accuracy. The coverage of the LiDAR datasets available is shown in Error! Reference source not found.. The green squares show where the high resolution 0.5m LiDAR data is. The purple shows the extent of the 1m and 2m LiDAR data.

22 Figure 1-1: LiDAR Coverage in Stockton BC 4$6 10=>, LiDAR coverage in Stockton BC8 G& 44 $44 %&&, 1.5 Historical Flooding There are a number of sources of historical flood information. The majority of historical data collected was received from key stakeholders during the SFRA consultation process or by reviewing past flood studies in the area. Studies which have provided details on flood history include: 0)&6!" &* %B &&* & ' * &3%& %B &&* &6 The British Hydrological Society s Chronology of British Hydrological Events also provides some descriptive information of past flooding events in the Tees Valley. This goes back many centauries but is more consistent after Key holders of historical flood data are identified below. All the data has been combined to provide a historical flooding GIS based dataset. This will be mapped for the SFRA and can be used by the LPA for future development planning and can be supplied to developers for site specific Flood Risk Assessments. The historic flood risk locations are shown with the PPS25 Flood Zone maps in Appendix A, Figures A1 to A Environment Agency The Environment Agency is a key source of all flood risk information in England and Wales. As part of the Flood Map, the Environment Agency provides a national historical flood map layer. This shows the extent of major flood incidents. Those identified include:

23 January overtopping of the defence on the east bank of the River Tees (just upstream of the barrage) January flooding from the fluvial River Tees at Yarm and Preston on Tees Autumn overtopping of defences of the River Leven (rural location in the Borough) Stockton-on-Tees Borough Council Local Authorities can be an important source of historical flood information. Stockton BC has provided a wet weather list. This is a list of flooding hotspots from the Stockton BC drainage and highways engineers. This was converted to GIS and shows flooding locations distributed across the urban locations within the Borough. This contains information on all sources of flood risk especially surface water flooding. This will be a useful data source to compare with the Environment Agency s theoretical surface water flooding maps. In addition, a GIS dataset was available from the 2007 SFRA showing fourteen flooding locations. This dataset contains flooding locations that have been reported by Stockton BC. The data includes a short description of the incident and a date Cleveland Fire Brigade Cleveland Fire Brigade has provided geo-referenced data in spreadsheet format of all water related call outs since over 300 flood related callouts since August This has been edited (excluding burst pipes etc) to around 120 flooding incidents and converted to GIS. These locations have also been mapped along with all other historical data collected Cleveland Emergency Planning Unit Cleveland Emergency Planning Unit (a consortium of emergency planners covering the Cleveland local authorities) provided a list of historic flooding locations. This Unit only responds to large scale events, where coordination of different emergency response organisations is required. As a result, information on only four incidents was provided Other sources Ron Watson, who is the Flood Defence Manager for Northumbria, was able to provide historic flooding information for the main flood risk locations of the last 50 years. The Highways Agency and Northumbria Water were contacted for flood risk information. Unfortunately they were unable to provide any information for the study. Northumbria Water is waiting for confirmation on what type of information they can legally provide. If information becomes available in the future, this can be used to update this Level 1 SFRA. 0

24 0!!(+" #!!*-#!!+!" 2.1 Introduction There is a need to understand the risk of flooding from all sources in the Borough, consider where the most at risk locations are, and plan future development and regeneration accordingly. This section assesses flood risk in the Borough from all sources, now and in the future. It makes use of all the data and information described in Section 1. It includes providing the tidal and fluvial Flood Zones and assesses flood risk from other sources, with the aim of providing enough information for the Council to perform the Sequential Test. The major watercourse in the Borough is the River Tees which originates outside of its administrative boundary. There are also a number of smaller watercourses which generally flow northeast and southeast through rural land and then through the Borough s urban area. Examples include Lustrum Beck and Billingham Beck. The main source of flooding to the Borough is tidal and fluvial from the River Tees and other urban watercourses. The tidal flood risk is particularly extensive, placing large parts of the industrial area on the north bank of the Tees Estuary and other, more central parts of the Borough, at risk. Tide locking (prevention of fluvial flow discharging due to high tide levels) is also a contributing flood risk factor on many watercourses that flow into the tidal Tees. The historic flood risk information collated during this study also shows the distribution of other sources of flooding, the main being surface water flooding. Although the mapping shows a wide distribution of such locations (see Figures A1 to A8 in Appendix A), surface water flooding is not necessarily as significant as it may seem due to the small scale and low hazard of the flood events. Many of the points, for example, indicate only very localised pooling of shallow water after heavy rain. 2.2 Tidal Flood Risk The breakwaters at North and South Gare mark the mouth of the Tees Estuary. The upstream tidal limit previously extended to Low Moor, which is upstream of Yarm, but it is now the Tees Barrage. The barrage was opened in 1995 and it prevents tidal ingress and has created a new 16km stretch of non-tidal water, used for recreation purposes. The Tees Barrage is discussed in the defences section of this chapter (2.10.4). The area of the Borough around the Tees Estuary downstream of the barrage is vulnerable to high sea levels. This can arise from a combination of high tides, storm surge, the action of waves and, in some cases, the joint impact of fluvial flows and tidal levels. Extreme tide levels for the Tees Estuary, shown in Table 2-1, have been taken from the Draft Tees Tidal Flood Risk Management Strategy (Environment Agency, February 2008). These levels (and climate change levels) are the current Environment Agency recommended levels for assessing tidal flood risk in the area..

25 Table 2-1: Extreme tidal level estimates for the Tees Estuary ;<$6!( 7 ) 6<7 );;< 6@7 033A A Within the estuary, mean high water springs are 2.7m AOD and the highest astronomical tide is 3.3m AOD. The highest recorded water level of 4.0m on the Tees Estuary was a result of a large surge tide (1953 event). Sea levels on the Tees are forecast to rise by 255mm over the next fifty years as a result of sea level rise. Although stormier conditions can be expected in the future, any impact in terms of increased wave heights within the estuary adjacent to the Borough will probably be of little consequence compared with the impact of sea level rise. Flood defence and artificial ground raising protect much of Stockton BC from tidal flooding. There is the potential for some defences to be outflanked, notably those at Port Clarence, Old River Tees and at Greatham Creek. Flood defences are discussed in more detail in section 2.10 of this chapter. Flood risk problems in areas potentially affected by high tides are exacerbated by the series of urban rivers that drain into the Tees estuary. These include Lustrum Beck (joining the Tees at Stockton) and its neighbour Billingham Beck. Both are discussed in the fluvial flooding section of this chapter. Tidal risk is predominant but concurrent high river flows can exacerbate flooding if tide-locked Greatham Creek Within the Borough, Greatham Creek is a tidal watercourse which flows in a westerly direction, following the Borough Council boundary, and discharges into the Tees at Seal Sands. Its tidal limit extends to a weir, which is 300m upstream of the confluence with Cowbridge Beck, outside of Stockton Borough. The is crossed by bridges which carry the A178 trunk road and the emergency access road to Seal Sands. There is a history of tidal flooding and breach of the defences at Greatham Creek. Some details are provided in below Flood history There is a history of flooding from the Tees Estuary, including areas in the Borough. Flooding problems are focused around the Holme Fleet area near Port Clarence where flooding occurred twice in 2000, but there is flood history elsewhere. The BHS Chronology of British Hydrological Events contains the following records: Tidal flooding in Stockton Parts of North Ormesby flooded including Toll Bar, Grange Road East and North Ormesby Road (all of which are in the borough of Middlesbrough) An area of low pressure, in conjunction with north westerly winds and a spring tide, caused a large surge. There were two breaches of the embankments at Greatham Creek and Port Clarence was flooded up to a depth of 1.2m. The peak water level was 4.01m AOD at the Tees Estuary. According the current predictions (see 2.8), this event is estimated to have a 1in 100 year chance of occurrence (in any one year).

26 The 1953 tidal flood affected large parts of Stockton including Port Clarence and the Tees Marshalling Yard area. During this event, the Greatham Creek North Bank and South Bank defences breached upstream and downstream of the A178 bridge. There was also a tidal breach of Greatham Creek North Bank and South Bank defences downstream of the A178 bridge in January In February 1983 there was another breach of Greatham South flood defence embankment upstream and downstream of the A178. This event had a peak water level of 3.65m AOD, which is a 1 in 10 year event, according to the latest extreme tide levels. The Port Clarence area has also flooded several times since the 1953 event either from high tide levels or combined tidal / fluvial events. Figure 2-1: Flooding at Port Clarence in 1953 Source: Draft Tees Tidal Strategy, February Fluvial Flood Risk The key watercourses in terms of fluvial flood risk include: River Tees upstream of the Tees Barrage River Leven Lustrum Beck Billingham Beck

27 Cowbridge Beck Old River Tees Holme Fleet In addition to fluvial flood risk problems, there are combined tidal / fluvial issues with the lower reaches of all of these watercourses apart from the River Leven, which flows into the fluvial Tees. Greatham Creek is fully tidal so is included in the previous section. Each of the main watercourses which pose fluvial flood risk in the Borough is discussed below River Tees The River Tees rises in the Pennines where it passes through Cow Green Reservoir and High Force Waterfall. Further downstream, it flows through Middleton, Barnard Castle and Yarm, where it is joined by the River Leven. Ultimately, it flows through the heavily urbanised areas of Stockton-on-Tees and Middlesbrough. On the rural Lower Tees within the Borough, flood flows from the Upper Tees and River Skerne are attenuated by significant overbank flood storage. Although much of this reach has flood defences, primarily built to protect agricultural land, they are overtopped or bypassed in major floods. Principal urban defences on the River Tees within Stockton BC exist at Yarm with a higher level of protection. Yarm suffers significant flood risk from the Tees. However, two schemes have been built (in 1993 and 1995) providing a standard of protection up to approximately the 1 in 20 year event. There is a long flood history at Yarm including the following years: 1635, 1642, 1753, 1761, 1763, 1770, 1771, 1783, 1789, 1792, 1822, 1829, 1837, 1869, 1872, 1875, 1881, 1886, 1892, 1924, 1940, 1968 and According to the Environment Agency s Flood Zone maps, parts of Stockton to the northeast and southwest of Victoria Bridge could also be exposed to fluvial flooding from the Tees River Leven The River Leven originates in the North Yorkshire Moors and is predominantly a river within the borough of Middlesbrough. The Leven converges with the River Tees at Yarm, within the borough of Stockton-on-Tees. The Environment Agency s historic flood outline, shows that overtopping of the defences at the River Leven occurred in Autumn 2000 at a rural stretch between Middleton and Ingleby Barwick. In November 2004, the River Leven at Yarm bursts its banks due to heavy rainfall at Leven Bridge. This event flooded houses and the carriageway at Leven Bridge. New development has been built above the highest recorded flood level and only the mill at Mount Leven is thought to remain at risk Lustrum Beck Lustrum Beck rises to the east of Darlington and flows in a north easterly direction to its confluence with the River Tees at Stockton. Lustrum Beck has a history of flooding dating back to The worst recorded event occurred on 29 th March 1979, during which there was substantial flooding of residential/commercial properties and land. Further flood events occurred in April, June, October and November 2000, all of which affected properties along the Beck. Within Stockton, the river corridor alternates between areas of dense urbanisation and public open spaces. There are numerous bridges and culverts in the urban and industrial areas. The lower reaches of Lustrum Beck can be tide locked due to its flapped outfall

28 arrangement. Lustrum Beck has some known flooding problems (e.g. at the Tilery site off Norton Road, Hartburn Lane, Oxbridge, Newtown and Primrose Hill). A flood risk mapping study has identified a large urban area is at risk from potential failure of the defences on Lustrum Beck, with 240 residential and 11 commercial properties at risk from a 1 in 100 year flood. Flooding on Lustrum Beck is the result of insufficient channel capacity and culvert blockages. This has been exacerbated over time by the loss of floodplain storage, as a result of industrial and residential development. The current standard of protection offered by the existing defences varies from the 1 in 10 and 1 in 5 year events. A flood alleviation scheme has been designed and partially constructed by the Environment Agency to solve some of these known flood problems. The preferred flood risk management solution identified by the Environment Agency s Lustrum Beck Flood Alleviation Scheme studies is flood storage in the upper catchment at Hartburn, with local defences at Oxbridge, Newtown and Tilery. In addition, the inlet to the Primrose Hill culvert is to be modified. The proposed standard of protection is to the 1 in 100 year event. The proposed flow control comprises a 7.5m high earth dam with a gated control structure to act as a throttle. The local defences comprise 1500m of walls and embankments, ranging in height from 0.5 to 1.2m. The works at Primrose Hill comprise reprofiling the entrance and lining part of the culvert to improve its hydraulic capacity Two unnamed watercourses flowing into Lustrum Beck The first unnamed watercourse is adjacent to Eastbourne Road and flows under the A177 and railway line. The culvert has a low hydraulic capacity (up the the 1 in 10 year event) and is susceptible to blockage. This watercourse does not give rise to flooding of properties due to the entrenched nature, and therefore high hydraulic capacity of the channel upstream of the culvert. However, some flooding of the A177 and allotment gardens on the left bank does occur in the upper reaches where the hydraulic capacity of the channel is more restricted. Spillage onto the A177 commences at the 1 in 25 year event. Flooding from the second unnamed watercourse off Swinburn Road is related to water backing up at the entrance to the culvert that flows under the adjacent housing estate. This is reported in the flood mapping study as being due to the culvert being subject to siltation problems. As a consequence, the flood waters cannot enter the culvert and the allotment gardens and open land upstream of the culvert start to flood at flows of the 1 in 2 year event. However, at the 1 in 10 year flows, the flood waters flow into the adjacent housing estate causing widespread flooding to properties in the vicinity of Brinkburn Road and Swinburn Road. The flood waters ultimately return to the unnamed watercourse at the downstream end of the culvert behind Swinburn Road Billingham Beck Billingham Beck is on the north bank of the Tees and runs parallel to the A19, where it is constrained by elevated banks. It has a free outfall to the Tees near Newport Bridge with most of the land at the confluence being industrial. Billingham Beck has been known to overtop its banks but as it has a wide floodplain. The areas affected by flooding are in Norton, Haverton Hill and Bishopton Bridge areas to the North of Stockton. However, much of this area is agricultural and also includes a golf course. However, there are few properties at risk of flooding Cowbridge Beck The catchment of Cowbridge Beck extends from Wynyard Park in the west to the culvert under the A1185 in the east. The upper reaches of the catchment are predominantly rural and rise to a level of approximately 120m AOD. The lower parts the watercourse is largely

29 urban. As it flows through Billingham and Wolviston Cowbridge Beck has caused concern in the past and for this reason it was re-designated as a main river in April Cowbridge Beck has a history of flooding problems from 1970 and 2004 affecting the Grange Avenue area. However, the only significant flood event occurred on Cowbridge Beck in March/April 1979 and was due to heavy rainfall. This resulted in the flooding of 68 properties in Halidon Way, Newbury Way, Neasham Avenue, Otterburn Way and Bannockburn Way. The properties on Halidon Way were so badly damaged that the tenants (they were mostly council houses) were re-housed and the demolition of the houses was considered by the council. The flooding was attributed to two main causes, firstly the insufficient capacity of the culvert under Billingham Campus (referred to as the Pennington Close culvert). The second cause was the poor drainage of Billingham campus playing fields Works were carried out to alleviate the problem. These included raising the ground levels alongside the headwall entrance to the same level as the headwall. This enabled the culvert to operate at a higher capacity. A maintenance regime was also implemented to keep the watercourse clear of debris, with particular importance given to the reach upstream of the culvert. There has been no repeat of the 1979 flooding since these measures were introduced Old River Tees The Old River Tees was the main channel of the River Tees before the current one was cut following an Act of Parliament in It now has a small catchment with inflows from Stainsby Beck, various land drains and a combined sewer overflow. Its tidal limit is a flapped outfall near the southern perimeter of the Tees Retail Park. The Old River Tees continues to the east of the retail park, under the A66 and the Tees Marshalling Yard, before it joins the estuary just downstream of the barrage. Tees Marshalling Yard flooded during the 1953 tidal event, but there is also fluvial flood risk from the Old River Tees. This watercourse poses a risk to the Tees Retail Park, a golf course and Tees Marshalling Yard. The Old River Tees flooded due to a blocked culvert in January The Tees CFMP also mentions surface water sewer problems on Acklam Road which can be exacerbated by high flows in the Old River Tees. New hydraulic modelling is required to identify the risk in more detail as the current Environment Agency Flood Zones modelling techniques are too generalised to reasonably represent potential flooding at this location Holme Fleet The Holme Fleet watercourse is situated on the north bank of the Tees Estuary. It extends from the south of Cowpen Marsh SSSI and flows to the north of Port Clarence before it passes beneath the A178. The catchment area is approximately 4.3km2. This watercourse is culverted under the railway and industrial land, and discharges to the estuary through a flapped outfall. Holme Fleet is important because it supplies fresh water to (and drains) the Teesside International Nature Reserve. There is also a history of flooding from Holme Fleet, but as the watercourse has an undeveloped floodplain, there are few problems associated with the flooding the occasionally occurs. In March 1999, due heavy rain, peak flows were unable to pass through Holme Fleet culvert, which is located to the north of Port Clarence. The culvert was blocked at the time by material which had entered the access chambers. This resulted in substantial flooding of the area. In April 2000, Holme Fleet culvert blocked again causing flooding of the area. The culvert was desilted by Stockton BC and improvements were made to the inlet. 1

30 A pre-feasibility study was completed in Spring This concluded that the risk presented from tide locking of the outfall is insignificant. The study concluded that future operations and maintenance activities along Holme Fleet should be focussed on keeping the culvert free from blockage. 2.4 Flooding from Land Historical flooding data Many of the historical flooding locations collated from the Environment Agency, Stockton BC and Cleveland Fire Brigade are located outside of the fluvial and tidal Flood Zones. These locations are therefore presumed to be related to other sources of flooding such as surface water. The information provided often states that flooding was due to surface water, blocked gulley s and minor watercourses. The distribution of these locations can be seen in Figure A, Appendix A Surface water maps The Areas Naturally Vulnerable to Surface Water Flooding Maps, based on the Environment Agency data are discussed in Section of this report. The surface water maps for Stockton are included in Appendix A (Figure E). These maps show the surface water flood extent and variation in vulnerability due to an extreme rainfall event. These maps should not only be used to assist the strategic consideration of the impacts of surface water flooding but also the sequential approach, the production of Surface Water Management Plans (SWMPs), and detailed FRAs for specific development proposals Screening of Critical Drainage Areas (CDA) SFRAs provide the opportunity for local authorities to assess at a strategic level, the risk from multiple sources of flooding, which can then feed into more detailed assessments where appropriate by both themselves and other operating authorities. This includes the identification of Critical Drainage Areas. Critical Drainage Areas (CDAs) are those areas identified from historical flood events and/ or modelled data as having a significant risk from surface water flooding. Recommendations can then be made for the future provision of Surface Water Management Plans (SWMPs) in high risk locations or areas of significant development for which an integrated drainage solution is possible that can reduce flood risk both to the development and elsewhere (SWMPs guidance is discussed in Volume III). Screening for CDAs within the Stockton BC area was undertaken using data from the following sources: Local authority flood risk locations Fire Brigade flood incident locations The national Surface Water Map (SWM) The Stockton BC area was assessed to try and identify if there are any particularly extensive areas covered by the SWM. At the same time, the area was assessed to identify any clusters of historical flood risk locations and incidents. If incident clusters and extensive SWM coverage overlap, this would be a good indication that there is a CDA. If incidents were in Flood Zone areas, these were ignored as they are probably due to river or tidal flooding. However, when reviewed, it was found that the flooding incidents are sporadically spread throughout Stockton BCs urban area. In addition, there are no distinct, extensive areas covered by the SWM (see Figure E in Appendix A). One area was identified that could potentially be a CDA and should be considered as a potential area of interest in a future Surface Water management Plans (SWMP). This is in Billingham, shown in Figure 2-2 below. The SWM is more extensive here but remote from /

31 any main rivers and ordinary watercourses. There are also around ten historical flooding locations in this area. These flooding incidents are described as basement flooding, general pooling and gulley problems (indicative of surface water flooding issues). Figure 2-2: Potential CDA in Billingham 4$6 10=> 744( &76 3&4& *&$8 %%& 3%& There are a number of significant, proposed development allocations for the Borough, the largest of which is the complex of allocations on the north bank of the Tees Estuary. The Seal Sands and Port Clarence allocations cover an area that is currently only partially developed. The SWM indicates that this area is potentially at flood risk. This is because the area is low lying and next to the Tees Estuary. The development of this area will have on site surface water management issues but because the site is next to the estuary on site storage and discharge should not be overly problematic.

32 Figure 2-3: North Tees proposed development area and SWM 4$6 10=> A review of the flood risk locations from the different data sources shows that Stockton BC has many areas of flood risk (of varying scales) away from the main rivers, ordinary watercourses and tidal estuary. This type of flooding is due to heavy rainfall events causing general ponding, surcharging of road culverts, flooding from blocked gulleys and overtopping of gulleys. This flood risk data will be used to provide evidence for the Sequential Test and it can be used by Stockton BC as a general flood risk database. 2.5 Flooding from Sewers The Draft Tees CFMP stated that there are problems with the sewerage system in Yarm. The CFMP also mentions sewer problems on Acklam Road (on the Middlesbrough BC and Stockton BC border) which can lead to flooding through drainage system overload. This can be exacerbated by high flows in the Old River Tees. Northumbrian Water has not been able to provide any historic foul and surface water flooding information. In addition, they were unable to provide information on future improvements. Northumbrian Water may be able to provide this information at a later date. However, in a document titled What Customers can Expect in (March 2005) Northumbrian Water proposed to either remove or provide mitigation measures that reduce the risk of flooding for all properties on the DG5 register, as of 31 st March 2005, by the end of 2009/10. Northumbrian Water had around 1.2million properties on the register and is

33 aiming to have no more than 76 properties remaining by the end of 2009/10. Also, the following sewer improvement schemes have been found on the Northumbrian Water website: Northumbrian Water is to begin a sewerage network upgrade to The Green area of Egglescliffe. The improvement work will involve constructing 250 metres of new sewer pipe along private farmland, from Manor Farm Pumping Station to The Green and will help to increase the capacity of the network and reduce the risk of flooding. A new pumping station, sewers and outflow at the Billingham sewage treatment works has recently been completed. Smaller works, at the feasibility stage, are to rectify flooding problems at Blackburn Close and Albert Road in Stockton. 2.6 Flooding from Groundwater The Draft Tees CFMP states that there is little documented evidence of groundwater flooding in the Tees catchment and groundwater flooding is not known to be a major problem due to the geology of the catchment. This is particularly true for Stockton BC as the main geology is of sandstone and mudstone. There are no sources of groundwater flooding as the aquifers within these sandstones are not artesian even in very wet conditions. When consulted on flood risk locations for this SFRA, the Environment Agency did not provide any information on groundwater flooding. 2.7 Flooding from Reservoirs & other Artificial Sources The Environment Agency was contacted for the location of major reservoirs in Stockton-on- Tees Borough. Within the register provided by the Environment Agency is a reservoir to the west of Longnewton (Longnewton Reservoir). This is in the middle of rural countryside. The area around the reservoir is generally flat and there are no settlements immediately below it. The main conurbation of Stockton is approximately 5 km away, between the reservoir and Stockton are several farm buildings. Due to the topography around the reservoir and the distance from any settlement, this reservoir requires no further flood risk assessment. The only other major reservoir on the register is Wynyard Lake. This lies to the west of Billingham and below Wynyard village. Below the main reservoir dam is rural countryside. The nearest settlement is Thorpe Thewles which is approximately 2.5km away. In addition, the topography in this area is not steep. As a result this reservoir requires no further flood risk assessment. 2.8 Effects of Climate Change Peak tidal levels from a range of return periods were taken from the Draft Tees Tidal Strategy. Table B.1 of PPS25 gives recommended contingencies for net sea level rise up to The levels in Table 2-3 have be estimated using the PPS25 guidance. The present day tide level predictions are the latest, recommended by the Environment Agency. 0

34 Table 2-2: Effect of sea level rise on water levels in the Tees Estuary Probability Tidal Levels (maod) in in in in in in UKCIP02 scenarios also suggest that winters will become wetter over the whole of England, by as much as 20% by the 2050s. A shift in the seasonal pattern of rainfall is also expected, with summers and autumn becoming much drier than at present. Snowfall amounts will decrease significantly throughout the UK, by the number of rain-days and the average intensity of rainfall are expected to increase. Rainfall intensity and the increase in the number of rain-days could have significant implications for surface water flooding and should be considered when designing drainage systems for new developments. Peak flow increase by around 20% over the next 50years will translate into higher water levels. Figure C in Appendix A shows the difference between the 1 in 100 year fluvial and 1 in 200 year tidal flood with the plus 100 years climate change extent. In Stockton BC, the extent of tidal flooding does increases in the Seal Sands industrial area. In addition, the tidal influenced reaches of Billingham and Lustrum Beck show an increased risk. The outlines also show that there could be a small increase in flood extent from the fluvial Tees, Lustrum Beck (fluvial) and Cowbridge Beck. The increase in extent will also mean an increase in flood depth and hazard for the existing areas at risk. Extracted from PPS25 Increases in sea level also have an impact on fluvial flooding due to backing up of tidal water. As a result, it is probable that there will be an increase in the instances of flooding occurring on: Old River Tees Billingham Beck LustrumBeck Holme Fleet.

35 2.9 Geology & Soils The geology and soils of the Borough were investigated using a strategic scale (1:250,000) map available from the National Soil Research Institute and can be viewed at: According to the soils map the majority of the Borough is covered by grass and arable land. This is slowly permeable seasonally wet loam and clay soils. This will impede natural drainage. The area around the Tees Estuary is arable with some grassland. This includes soils of the coastal flats. The loamy and clayey soil here is naturally wet and the water table is naturally high in these areas. Unfortunately the scale of this data makes it not particularly relevant at a local level, therefore it should be used only as an indication of the potential for groundwater and surface water flooding and a generalised dataset for the implementation of source control and infiltration sustainable drainage techniques (SUDS). Therefore, geology and soils should also be investigated at a site level during a FRA. Their characteristics are not the only considerations when designing SUDS. It is recommended (refer to Volume III of this SFRA) that the application of SUDS should be explored at an early stage of new development projects and design requirements documented within any FRA produced. More detail on the application of SUDS and the SUDS Management Train is also provided in Volume III Flood Defences The Environment Agency maintains records of all flood risk management assets using the National Flood and Coastal Defence Database (NFCDD) and this has been made available for this SFRA. The Draft Tees Tidal Strategy and the Lustrum Beck FAS study also provide useful information on the current defences and the potential future management of flood risk. The CFMP and SMP covering the Borough also provide a useful indication on likely future flood risk management policy. Likely future investment decisions can be inferred from these policy documents Fluvial defences There are formal defence on Lustrum Beck in Stockton that provide a standard of protection (SoP) up to the 1 in 10 year and on the Tees that protect Yarm up to the 1 in 50 year event. Lustrum Beck Lustrum Beck is defended for almost its entire length in the Stockton urban area. The defences were constructed in 1960 to a perceived 1 in 50-year standard. The Lustrum Beck Flood Alleviation Scheme (FAS) study (Environment Agency, October 2007) indicates that the fluvial reaches have a standard of protection of approximately 1 in 10 years, whereas the tidally influenced reaches have a standard of 1 in 150 years. The preferred solution to flooding from Lustrum Beck (as documented in the aforementioned FAS study report) is flood storage in the upper catchment at Hartburn, with local defences at Oxbridge, Newtown and Tilery. In addition, the inlet to the Primrose Hill culvert is to be modified. The proposed standard of protection is 1 in 100 years. Flow control comprises a 7.5m high earth dam with a gated control structure to act as a throttle. The local defences comprise 1500m of walls and embankments, ranging in height from 0.5 to 1.2m. The works at Primrose Hill comprise reprofiling the entrance and lining part of the

36 culvert to improve its hydraulic capacity. Once completed, this scheme will significantly reduce flood risk to Stockton from Lustrum Beck. However, only the Hartburn defences have been constructed so far. Further defences are planned for the proposed development at Tilery. But it is not known when funding will be made available for the remainder of the scheme. Lustrum Beck also has defences against tidal risk. At the confluence of the Tees with Lustrum Beck there is a flapped outfall, which is in line with the existing flood embankment. There are tidal defences at Portrack including Portrack Screens. The defences at Portrack provide a SoP against 1.1 in 25 year events. The Portrack Screens protect the Lustrum Beck catchment from flooding during periods of high tides in the River Tees. The concrete structure comprises steel debris screens, culverts and tidal flaps 2. CFMP policy in the area is to take further action to reduce flood risk therefore, a gradual programme of improvements should be expected with the aim of reducing tidal and fluvial flood risk. River Tees There are extensive sections of fluvial flood defences on the River Tees in the Borough. These defences mainly protect agricultural land from flooding but they also protect the town of Yarm. The original flood defences were at Yarm built in 1993 and The flood walls and gates at Yarm were upgraded to the 1 in 50 year event in The Draft Tees CFMP policy for flood risk management in the general area around Yarm is to take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits, locally or elsewhere in the catchment. This indicates that the defences may not be upgraded but flood storage may be used upstream to mitigate flood risk. The CFMP also states that where there may be benefits to urban areas, the Environment Agency may consider walking away from rural defences on the fluvial Tees in Stockton. This should be noted for future development planning. The Action Plan for the Middles Tees Policy Unit (includes Yarm) seems to confirm this as it includes the following: Produce and implement a System Asset Management Plan (SAMP) for the Middle Tees policy unit to determine the requirements for maintaining current infrastructure and channel structure whilst reducing surface runoff and increasing flood storage. Investigate the potential for creating further flood storage areas to manage flood risk both locally and downstream. This should also take into account the implications of climate change. If storage is increased by retreating from rural defences, fluvial flood risk to Stockton from the River Tees would also be reduced Tidal defences There are 11km of defences on the estuary downstream of the Tees Barrage. Those on the Tees are primarily located at the confluence with Lustrum Beck and at Port Clarence, downstream of the Transporter Bridge. There are also extensive defences along Greatham Creek. In addition, there is an earth embankment at Teesside Retail Park, which separates the retail development from the Old River Tees. The Environment Agency is responsible for 5( * " & & " (6 &* 0,!$ $ $& %76!6&C&,

37 maintaining all of these structures. Other third party assets include an embankment at the Tees confluence with Billingham Beck. The Tees Barrage, operated by British Waterways, is the effective tidal limit of the Tees Estuary. Although not primarily a flood defence structure, it does offer some protection against tidal flooding. It acts as a weir that prevents tidal ingress upstream. The Tees Barrage is discussed in Section Rising sea levels over the next 100 years will increase the flood risk on the Tees Estuary and tidal tributary. Unless action is taken, the standard of protection provided by the existing defences will progressively reduce and hence the chance of them failing will also increase. Maintaining and enhancing the existing tidal defences is necessary and the Draft Tees Tidal Strategy is currently developing options for improving flood risk management on the Tees. Tees Estuary Areas adjacent to the estuary are protected to varying degrees by flood defences or artificially raised ground levels. Flood defences have been constructed with a range of materials in a variety of forms. They are currently in fair to good condition (in accordance with the Environment Agency s..add reference..); however their remaining life span is varied. The embankments along the realigned River Tees were built during the 19th century. Iron works slag was used in their construction, the inner or single banks are constructed of sand with a pitched stone facing or clay. The tidal outfall at Portrack (outfall of Lustrum Beck into the Tees Estuary) was reconstructed in 1998 to prevent tidal inundation of the lower reaches of Lustrum Beck Greatham Creek The defences at Greatham Creek were also built in the 19th century. These have been breached in the past (see the flood risk section). Because of concerns over the level of protection the defences offer, the condition of the defences were investigated in the early 1990s. The embankments were found to comprise a mixture of clay, sand, gravel and slag boulders. Their composition, profile, face protection and crest level vary with length. The embankments were considered to be in good condition in general, although appropriate face protection is critical where the embankment is sandy. Some improvements were carried out to the east of the A178 but elsewhere little, if any, work has been undertaken. The CFMP policy for the area that includes these defences is to take further action to reduce flood risk. The Tees Tidal Strategy will outline the specific actions that need to be carried out in the area to manage the risk of flooding now and in the future (see section ). Old River Tees There are 1.04km of raised defences along this watercourse. The earth embankments near Teesside Retail Park (which separates the retail development from the Old River Tees) could be breached or overtopped. There is also the Old River Tees Tidal Control Structure (as named in NFCDD). This features two reinforced concrete headwalls with wingwalls, situated under the flood embankment system protecting the Old River Tees from high flows in the Fleet and Tees rivers ( *"6,.,@&" & &" (6&*,%!( $& %76!6&C&,

38 The Draft Tees CFMP policy for these defences is to continue with existing or alternate actions to manage flood risk at the current level. This means that there is unlikely to be any improvements in the standard of protection provided by flood defences. However, it should be emphasised that this does not mean existing defences will be left to decay and there may still be specific localised improvements in standards of protection. Indeed, the Draft Tees Tidal Strategy proposes that a flood control structure is constructed on the Old River Tees (in 5 to 25 years) and local defences and maintained and reconstructed as necessary (in 25 to 100 years), see section This is important as the Tees Marshalling Yard (near to the retail park) is a proposed development allocation. Standard of protection form tidal defences The Draft Tees Tidal Strategy estimated the standard of protection the tidal flood defences offer. This was based on overtopping and breaching calculations. The table below is extracted the Draft Strategy. This shows that due to sea level rise (as a result of climate change), there will be a very high annual probability of tidal flood defences failing in 100 years time. Improving the standard of the defences is therefore essential and the Tidal Strategy supports this.

39 1

40 Extract from the Draft Tees Tidal Flood Risk Management Strategy (Environment Agency, February 2008) /

41 Preferred future management options for the tidal defences The Draft Tees CFMP recommended taking further action to reduce tidal flood risk to Stockton from the Tees. The Tees Tidal Strategy is presently being finalised and also recommends reducing the risk of tidal flooding from the Tees Estuary. The following table, extracted form the Draft Tees Strategy, summarises what the preferred flood risk management options are likely to be for the Tees Estuary. Extract from the Draft Tees Tidal Flood Risk Management Strategy (Environment Agency, February 2008)

42 The table shows that all the defences are to be upgraded (eventually) which will leave a generally low risk of tidal flooding to urban parts of the Borough from tidal flood risk in the long term. Abandon defences The Strategy also states that there are a number of flood defence assets that may have previously fulfilled a purpose but due to land use changes / priorities they are no longer required. This means that the existing defences in the western area of Greatham North may be abandoned as the preferred option involves setting back the defence line. Following construction of the new defences along the western edge of the A178, a section of the existing defences would be removed to allow regular tidal inundation. The remaining lengths of the existing defence would be abandoned and left to degrade with time Tees Barrage The River Tees Barrage and Crossing Act 1990 empowered the Teesside Development Corporation to construct a barrage in and across the River Tees and complete other associated works. The River Tees Barrage was constructed in 1995 and primarily aims to provide a large range of environmental and planning befits to the tidal River Tees. A number of models have been used in the design of the Barrage, both mathematical and physical. A 1 to 30 scale model was constructed covering a 1km stretch of the River Tees. The main works during the construction of the Barrage consisted of: A barrage - which comprises of four fish belly gates A navigation lock, mitre gates and tidal exclusion gates A fish pass A canoe slalom Several bridges and associated road works, a slipway, sewer diversions and other minor works The Barrage forms an artificial barrier between the Tees Estuary and the upstream catchment. The barrage raises water levels to 2.65m AOD (MHWS tide level) on the reach from Stockton (just upstream of the Old River Tees junction) to Yarm. This is for amenity purposes, eliminating tidal effects, including the transfer of pollutants. Flood defence capability Although primarily designed for environmental purposes, the barrage does provide some flood defence and drainage capability. The barrage is capable of holding back tides to a level of at least 5.0m AOD (the level of the adjacent side walls of the structure). This level is approximately equivalent to the 1 in 1000 year + 75 years climate change extreme tide level. The barrage does not reduce fluvial flooding but it was designed to minimise the impact on upstream levels. The operating procedures for the barrage were investigated by HR Wallingford (1994 and 1996) to ensure that the impact of the barrage is minimised during high flows. During the design of the barrage, hydraulic modelling was undertaken to investigate the impact of the barrage on flood risk. Four joint probability (tidal and fluvial) flood events were modelled. Tests were also carried out on the 1 in 100 year fluvial flood with high water spring tides. The modelling confirmed that the barrage would not raise flood levels at Yarm by more than 0.25m. This was allowed for in the design of the Yarm flood protection scheme. The barrage is operated automatically with manual override available. There is a residual risk of increased upstream fluvial flooding if levels are kept high due to equipment failure (gates getting stuck in an upright position), manual override and wrong level/flow data.

43 There is also a residual risk of upstream tidal flooding if the gates stuck in a lowered position during a high tide event. However, the undefended tidal flood risk (excluding the presence of the barrage) is low due to raised land levels. The remainder of this section provides additional detail that may be useful reference material. Levels Mean high water spring tide (at Teesmouth) m AOD Target level of upstream river m AOD Normal amenity range of upstream river between 2.35 and 2.85m AOD Highest surge tide recorded at barrage site 4.01m AOD Ground levels generally around site (raised) m AOD Operational objectives The primary operational objective of the barrage is to maintain an upstream river level at approximately the height of MHWS at Teesmouth (between 2.35m AOD and 2.85m AOD). With the normal target level being 2.65m AOD measured at the barrage. This level is maintained for the following reasons: To provide fresh water upstream of the barrage (for aesthetic purposes) For the functioning of an international standard canoe slalom To enable upstream and downstream passage of leisure craft To ensure that the rise in upstream levels caused by the barrage does not increase the risk of flooding and potentially adverse effects on land drainage To provide passage of migratory fish as required by the Salmon and Freshwater Fisheries Act (1975) and provide passage for eels To assist in the desilting of the upstream river In the operational procedures and control rules established to meet the operational objectives there are 10 priorities listed. The first two being, protection of life and property and avoidance of flooding or serious drainage problems. The text below does not make sense unless you briefly explain the nature of the gates (they appear to be lifted to close them is this correct) Operating levels The barrage has its own local telemetry\scada system with automatic control to achieve an operating band level of m AOD. The barrage can be controlled automatically or manually and there are three identified states of control. State 1 - low or normal river flow. The majority of the time, the upstream river flow is taken by the slalom and fish pass and the main gates are not required to discharge water. The upstream river level is maintained within the preferred band of 2.5 to 2.65m AOD. If the level goes above 2.65m AOD, one or more of the gates are lowered to maintain the water level within the preferred band. If the upstream level falls below 2.65m AOD all the gates are raised to a park level and all flow is stopped through the slalom. If a high downstream tide level comes within 250mm of the upstream river level the gates are raised by 200mm. State 2 - medium river flow. During medium river flows the upstream river level is maintained within the preferred band of +2.5 to +2.65m AOD. If the level goes above 2.65m, one or more of the gates are lowered to maintain the water level within the preferred band. 0

44 State 3 - high river flow. During high river flows, the gates are stepped downwards in 100mm steps to maintain the upstream river level within the preferred band. If water levels increase, the step size is increased to 200mm. If a high river flow coincides with a high tide, the above principles still apply, but gates are raised by one step to ensure flows are always moving downstream and keeping tidal water out of the upstream river Flood Warning Areas The Environment Agency has the lead role in providing flood warnings service in England and Wales. The aim of the flood warning service is to reduce risk to like, distress to people and damage to property caused by flooding by providing accurate, timely flood warnings to residents within the floodplain of rivers, estuaries and coasts; to the media and partner organisations. It is crucial that people at risk receive appropriate flood warnings and take action to protect themselves and their property. Within the Environment Agency corporate plan Creating a Better Place 4 the Agency has highlight three main targets: To have 80% of properties at risk in the floodplain in England and Wales receiving and appropriate flood warning service, 75% of people who live in flood risk areas take appropriate action by 2011, To have major incident plans in place for high flood risk areas. Currently the Environment Agency operates a flood warning service in specific locations known as Flood Warning Areas where Flood Warning Codes are assigned based on the overall impact of flooding within an area. These codes include: Flood Watch Flood Warning Severe Flood Warning All Clear flooding of low-lying land and roads is expected flooding of homes and businesses is expected severe flooding is expected all clear or receding floodwaters The Environment Agency s Floodline Warnings Direct service provides flood warnings direct to people by telephone, mobile, , SMS text message, fax or pager. There are a number of Flood Warning and Flood Watch areas that cover the Borough, some of which cross over administrative boundaries. Figure D in Appendix A show the Flood Warning Areas. They include: River Tees At Yarm - properties in the High Street and adjoining streets / 5( *"6=> && & $ & &6.

45 At Thornaby - commercial properties on Boathouse Lane Lustrum Beck At Stockton - properties on Hartburn Avenue, Burnside Grove, Burnside Court and Oxbridge Lane Tidal Tees At Portrack - commercial units at Portrack At Port Clarence - residential, commercial and industrial premises behind tidal flood defences in Port Clarence At Teesside Park - usinesses on Teesside Park At Greatham Creek - the heavy engineering basin in the north west corner At Billingham Reach - orks adjacent Haverton Hill Road At Haverton Hill - esidential properties and small industrial units at Haverton Hill Flood Warning Areas are covered by Floodline Warnings Direct.

46 2 -!!(+.))"- 3.1 Introduction The investigation and identification of the extent and level of flood risk to an area is assessed primarily geographically. Whilst the Environment Agency s Flood Maps are very useful in this respect in showing indicative land use planning zones as required by PPS25, they are only a starting point in the consideration of flood risk in a particular area. PPS25 Flood Zone Maps should be used primarily to enable the Sequential Test to be carried out, firstly in avoiding inappropriate development and then secondly, to seek compatibility between flood risk vulnerability and Flood Zones as required in Table D3 of PPS25.However, more detailed analysis is often needed to gain a greater understanding of the varying degree of flood risk at a district level. At this SFRA level, it is not appropriate to look at flood risks in detail for individual development allocations, as this is a requirement of the site specific FRA and will be undertaken by developers in respect of specific development proposal and prior to submitting a planning application. However, there is a need to undertake a broad assessment of flood risk issues to assist the LPA in making the spatial planning decisions required. This will enable a degree of certainty that the proposed development allocations put forward in the LDD, allow compliance with the Sequential and Exception Tests in PPS25 and importantly provide information to test whether the developments should be safe for occupants and users. This broad assessment is assisted greatly a suite of council scale flood risk information and include the PPS25 Flood Zone Maps. No one map should be considered in isolation without reference to the others. The set of Strategic Flood Risk Maps provided in the Stockton BC Level 1 SFRA can be found in Appendix A and include: SET A: SET B: SET C: SET D: SET E: PPS25 Flood Zones Flood Zone 3 Depths Climate Change Sensitivity Flood Risk Management Measures Areas Naturally Vulnerable to Surface Water Flooding After the PPS25 Flood Zone Map has been used to carry out the first sweep or Sequential Testing for various proposed development locations, all sets of maps need to be interpreted consistently in order to complete the second or third pass of the sequential approach sieving process. They can also be used outside of the development planning process to gain an understanding of various flood risk factors in other areas of interest across the Borough. 1

47 The detail provided in the Strategic Flood Risk Maps may also facilitate the application of the Exceptions Test where applicable. These maps should be used in sequence as shown in the Sequential Test sieving process as shown in Volume I of the SFRA. 3.2 PPS25 Flood Zones Maps The PPS25 Flood Zones have been produced on a set of eight maps covering the Borough (see Appendix A Figures A1 to A8). The fluvial Flood Zone maps are based on information provided in the Environment Agency Flood Map. Version 3.13 of the Environment Agency Flood Zones issued in March 2009 has been used as the latest flood zones in this area. Flood Zones 2 and 3 were checked against all the most recent modelling outputs to see if they had all been integrated. Both Flood Zones 2 and 3 appear to have been updated with all the currently available hydraulic models. As stated in PPS25, a normal aim of SFRAs is to define Flood Zone 3b: the functional floodplain. In this SFRA, this has been delineated using the method outlined in section These key maps should be used for the facilitating the undertaking of the Sequential Test by planners and developers according to PPS25, as discussed previously in Volume I and illustrated within stage 1 of the Sequential Test sieving process Tidal Flood Zone map JBA Consulting does not regard the current Environment Agency tidal Flood Zone 2/3 definition as being sufficiently accurate for use by this SFRA. Therefore, a tidal model was used to produce the tidal Flood Zone in replacement of Version 3.13 of the Environment Agency Flood Zone maps (see section 3.2.1). The modelling was carried out using a standalone TUFLOW model that had previously been created by JBA for the project 2008s3456 (North East Assembly Regional Flood Risk Assessment). The modelling was carried out across an active 2D domain of approximately 135km2 extending from the mouth of the Tees estuary to Eaglescliffe upstream of Stockton on Tees. The TUFLOW model grid was created with a 2D cell size of twenty metres from a DTM with a cell size of five metres that had previously been constructed from a combination of filtered LiDAR. Formal (NFCDD) defences were removed from the model by interpolating ground levels across defences. A tidal graph for four different events was derived by scaling the storm surge associated with an existing tidal graph of the Tees estuary to match the relevant extreme tide level. The models were run for three tidal cycles during which the storm surcharge shortly precedes (by 4 hours) the second cycle. Figure 4-1 shows the approximate tidal graphs for the four modelled events. 1

48 Figure 3-1: Tidal graphs for modelling sea level in the Tees Estuary The 1 in 1000 and 1 in 200 year events (Q1000_2080 and Q200_2080) were mapped to represent Flood Zones 2 and 3 in the SFRA. The 1 in 200 year event with plus 100 years climate change (Q200_2108) was also mapped. It was decided that the 1 in 25 year event (Q25_2080) would not be used in the SFRA as the definition of the functional floodplain is not required for tidal flooding. Levels for the tidal modelling were taken from the Draft Tees Tidal Strategy (the latest Environment Agency approved levels). The climate change levels were also taken from this study, which are based on the latest Defra / PPS25 guidance (Supplementary Note to Operating Authorities Climate Change Impacts Defra, October 2006). The tidal model is based on different levels and different elevation data to the Environment Agency Flood Zone maps. As a result the draft extents are significantly reduced in some locations. This is can be clearly seen on the Sealand Sands Industrial land and Saltholme areas, north of the Tees Estuary and the stretch of the Tees from the Barrage to Haverton Hill (see Figure A1 in Appendix A) Functional Floodplain The Functional Floodplain (Flood Zone 3b) has been defined using modelled 1 in 25 year outlines where available. The modelled outlines were then edited using the following methodology: Exclusion of purely tidal areas Inclusion of land which provides a function for flood conveyance or flood storage (e.g. washlands) Removal of areas benefitting from defences (ABDs) Removal of developed (Brownfield) land Removal of major transport infrastructure (e.g. motorways and railways) Removal of dry islands defined using the size standards within the Environment 1

49 Agency SFRM Specification for Flood Risk Mapping 5 For those watercourses that have not been modelled, Candidate Flood Zone 3b areas have been identified based on the Environment Agency Flood Zone 3 outlines. Greenfield areas within Flood Zone 3 have been identified which should be safeguarded from future development. Storing flood water in these areas during an event could potential reduce risk downstream at urban areas in the future. However, as these areas have not been explicitly modelled and are partly based on profession judgement, it is important that they are assessed in more detail at a site-specific FRA level if development is planned in the future. However it is recommended in this SFRA that they are left as open greenfield for future flood storage or as flood compensation needed to allow other development. The data used to define the functional floodplain and Candidate Flood Zone 3b for each watercourse is summarised in Table 3-1. Table 3-1: Functional Floodplain (Flood Zone 3b and Candidate 3b) Mapping, : ( Cowbridge Beck 1 in 25 year Cowbridge Beck Flood Mapping Study (2006) Lustrum Beck 1 in 25 year Lustrum Beck Data Improvements (Black and Veatch, Marsh 2008) River Tees (fluvial) Unnamed watercourses that converge with Lustrum Beck Remaining locations 1 in 25 year River Tees Model Update (2007) 1 in 25 year Dales Area Floodplain Mapping (2005) 1 in 100 year Candidate Flood Zone 3b areas using Flood Zone Flood Zone 3 Depth Map An indicative depth map of a 1 in 100 year fluvial event and 1 in 200 year tidal event has been provided for Stockton BC (see Figure B1 in Appendix A). The tidal depth grid was created using the new tidal TuFlow model (see section 3.2.1). The fluvial depth grid was obtained from the Environment Agency North East broad scale modelling work for CFMPs undertaken by JBA Consulting in The methodology is based on the original methodology used in creating the original Environment Agency Flood Map using an overland routing model JFLOW. However, the map was improved by: Updating the hydrology of inflows into the model, and Updating the topographical data from NEXTMAP to LiDAR data. Flow paths under structures were also included to provide a more realistic result. Whilst the extent of the depth grid cannot be directly compared to the current Flood Zones (as Flood Zones are based on detailed hydraulic models in some locations and NEXTMAP extents in others) they do provide an useful indication of potential scale of flood inundation during a 1 in 100 year event. 5( *"6=>$"# %$"# % &, 11

50 The depth map has been categorised in depth ranges using the scaling below: Max Depth (m) >3 3.4 Climate Change Sensitivity Maps Where there is modelling available, climate change sensitivity maps have been provided (see Figures C2 to C5 in Appendix A). These maps show fluvial flood extents for an undefended floodplain with a 1 in 100 year flood flow plus a 20% increase in flood flows. This is representative of a plus 100 years climate change extent. For un-modelled watercourses the presumption is to take Flood Zone 2 as a precautionary extent of Flood Zone 3a in the future. The 2D TUFLOW model of the Tees Estuary was has been used to show the impact of climate change on tidal flooding (1 in 200 year event plus 100 years). The increase in sea levels due to climate change on the Tees Estuary is shown in section 2.8. The sequential approach requires early consideration of the effects climate change on flood risk and these maps help greatly in this respect. PPS25 requires the consideration of the sensitivity of new developments to climate change to be considered as part of an appropriate FRA and these maps provide an indication of this sensitivity. In addition, emergency evacuation routes can be identified and planning put in place to ensure they are outside of the flood extent. The sensitivity of a particular location and land use to climate change can be factored into decisions regarding floor levels, building uses and safe access and egress etc. Greater changes in depth or extents can be associated with greater increases in flood risk and in these areas, where this risk cannot be avoided, or substituted, mitigation measures are likely to be extensive. For some developments, the FRA may not be able to demonstrate continued safety for occupants as required by the Exception Test in PPS Flood Risk Management Measures Maps Residual risks are the risks that remain after all risk avoidance, substitution and mitigation measures have been taken. The residual risks in the Borough are therefore related to the occurrence of events of low probability, such as extreme flood events greater than the design capacity of the constrained river/coastal system or where the design standard of flood defences is exceeded. A map of flood risk management measures has been produced (see Figure D in Appendix A). The map includes the: location of Environment Agency river flood defences location of coastal defences coverage of Environment Agency Flood Warning Areas This map is very important when considering the residual risks associated with flood. These residual risks must be investigated within any Level 2 SFRA or site specific FRA as relevant. 1/

51 3.6 Areas Vulnerable to Surface Water Flooding Maps The Areas Vulnerable to Surface Water Flooding Maps show actual surface water flood extent and variation in depths for particular geographical areas of interest, assuming a 1 in 200 year rainfall event and a hard surface ground model. The areas vulnerable to surface water flooding zones have been provided on a set of eight maps, and are largely based on information provided in the Environment Agency national Surface Water Map (see Figures E1 to E8 in Appendix A). The vulnerability zones are split between three zones: More Vulnerability Vulnerable Less Vulnerability These maps are extremely helpful in supplementing the PPS25 Flood Zone Maps as they show where localised, flash flooding can cause problems, even if the Main Rivers are not overflowing. More information on surface water flooding and the surface water flood maps can be found in section of Volume I. 1

52 4 )!!" 4.1 Introduction A Level 1 SFRA should enable Stockton BC to carry out the Sequential Test as outlined in Annex D of PPS25. This Level 1 SFRA has provided Stockton BC with PPS25 Flood Zone classifications for all locations identified for development provided within this assessment. The Council will be required to prioritise the allocation of land for development in ascending order from Flood Risk Zone 1 to 3, including the subdivisions of Flood Risk Zone 3, if necessary. The Environment Agency has statutory responsibility and must be consulted on all development applications allocated with medium and high risk zones, including those in areas with critical drainage problems and for any development on land exceeding 1 hectare outside flood risk areas. In these circumstances, the Environment Agency will require the Council to demonstrate that there are no reasonable alternatives, in lower flood risk categories, available for development. Where appropriate, the Exception Test is to be applied. A Sequential Test spreadsheet has been produced showing the results of all allocations provided by Stockton BC against PPS25 Flood Zones and as an extra layer of information against the surface water vulnerability zones. Area (ha) and percentage cover of each Flood Zone is provided. A screenshot of the spreadsheet is provided below. The full spreadsheet is included in B. Figure 4-1: Screenshot of Sequential Test Spreadsheet Stockton BC should use this information to carry out the first sieve of the Sequential Test, by identifying and removing those sites at greatest risk. Once a decision has been made by Stockton BC on whether to remove or keep (due to wider social/economic reasons) 1

53 those sites at higher risk, they should then carry out a second or third pass of the Sequential Test against the wider suite of flood risk maps produced within this SFRA. This should ensure that there is an evidence base for replacing sites at a high risk of flooding with those that are at a lower risk. Or for keeping the sites and bringing them forward for the Exception Test. Once the sequential sieving process has been carried out, the Environment Agency will require the Council to demonstrate that there are no reasonable alternatives in lower flood risk categories available for development. The vulnerability of the remaining sites at risk should be considered and substituted with lower risk development (if possible) before any mitigation measures are considered. The next part of this chapter summarises flood risk to the proposed development allocations that Stockton BC have provided for this study. Recommendations are then made for the content of a Level 2 SFRA. 4.2 Current Development Site Sequential Test Development sites identified by Stockton BC include: Available Employment Land Strategic Housing Land Availability Assessment (SHLAA) sites over 1ha Including the Available Employment Land and Stockton BC s SHLAA dataset, the total developable area is around 1060 ha. Table 4-1 and Table 4-2 provide a summary of sites at risk of fluvial and surface water flooding that are included in the Sequential Test spreadsheet Summary of sites at risk of fluvial flooding Table 4-1: Summary of Development Sites at Risk of Fluvial & Tidal Flooding = =0 =2 =2; "& "& "& "& Total ha of sites are at risk of flooding in the 1 in 100 year outline (Flood Zone 3a+3b). Out of 21 sites in Flood Zone 3a on average 22% of each site is at flood risk. 202 ha of sites are at risk of flooding in the 1 in 100 year event (Flood Zone 2+3a+3b) Out of 31 sites in Flood Zone 2 on average 31% of each site is at flood risk. 5 employment / housing sites are situated in the functional floodplain and under PPS25 these will not be permitted. However, the areas considered functional floodplain are relatively small (a total of 5ha and on average cover 6% of the site itself). It should be possible to redefine many of these site boundaries to make development acceptable. 10

54 4.2.2 Summary of sites at risk of surface water flooding Table 4-2: Summary of Development Sites at Risk of Surface Water Flooding > ;< = ;< # ;< "& "& "& "& Total The risk of surface water flooding to Stockton BC s allocations is potentially of a greater scale to fluvial and tidal flooding. 93 of the 108 sites are at some vulnerability to surface water flooding, this constitutes to around 20% of the designated footprint of development. A total of 10 sites have a high vulnerability of flooding which must be considered within the Sequential Test sieving process. If these sites go forward and are developed, a FRA must consider surface water mitigation techniques such as Sustainable Urban Drainage or a more open site layout. 4.3 Flood risk and the SFRA 2009 allocations Introduction The previous section combines Flood Zone and surface water map information with the proposed future allocations to allow the application of the Sequential Test. This section summarises where specific, generally larger, sites are at flood risk and includes recommendations for further work to assess this risk to an appropriate level of detail (i.e. in a Level 2 SFRA). For example, there are a number of sites adjacent to the River Tees that, due to tidal and or fluvial flood risk from the River Tees, are within Flood Zone 3 and 2. If no alternative lower flood risk sites can be found, further work will be required to be bring them forward for development. In addition to the work completed in this Level 1 SFRA, work completed in the Scoping Stage and discussions with Stockton BC identified a number of sites that would need assessing in a Level 2 SFRA. These sites are know to be at risk of flooding but are integral to Stockton BC s own redevelopment plans and wider sustainability of the borough. Potential flood risk to the sites identified by Stockton BC and in this Level 1 SFRA are discussed here Sites at risk from the fluvial River Tees As described in Chapter 2 and 3, parts of the Borough are at risk of flooding from the fluvial Tees. However, much of the upstream reach has a rural floodplain so no future development is planned. The functional floodplain has been confirmed in the SFRA by defining much of this rural floodplain as Flood Zone 3b (functional floodplain). Bowesfield Riverside Phase 1 and 2 The Bowesfield Riverside Phase 1 and 2 sites are shown to be within Flood Zone 3 (see Figure 4-2 below, the proposed developments have back outlines). Parts of these sites are on undeveloped greenfield land and within Flood Zone 3a (blue) and 3b (yellow). An embankment is shown on the Environment Agency s national defences dataset (purple line), but the information in NFCDD states that this embankment provides no flood defence benefits, the functional floodplain is therefore still applicable. 1.

55 The boundary of this site should be moved as any proposed development would not pass the Exception Test due to either being in Flood Zone 3b or more vulnerable development on greenfield land being in Flood Zone 3a. The remaining areas at risk will need further examination in a Level 2 SFRA. Modelling how development affects surrounding properties would be appropriate. The Phase 1 development has the potential to increase flood risk to Phase 2 if current flood storage is replaced by the development. The Phase 1 section of the Bowesfield site has had a FRA carried out by MWH. This should be reviewed as it will have implications for Phase 2 and appropriate mitigation measures adopted on site. Figure 4-2: Bowesfield Riverside sites with Flood Zone 3a, 3b and the raised defences 4$6 10=> Boathouse Lane and Chandlers Wharf The Boathouse Lane and Chandlers Wharf sites are shown to be within Flood Zone 3a of the fluvial Tees. These sites are on brownfield land and there is no Flood Zone 3b. For a Level 2 SFRA, these sites can be assessed using the current 1D River Tees s hydraulic model. Reviewing the model will allow for an initial assessment of the sites and the current flood mechanisms on sites. Fluvial risk to these sites depends largely on topography. The right bank (looking downstream) has been developed with riverside apartments, which have raised floor levels. Mirrored residential development is expected on the left hand bank. 1

56 Raising floor levels or constructing river defences could alleviate the problem allowing development; however this could potentially increase risk further downstream or to surrounding properties on the opposite bank. By removing the flood storage on sections of the left hand bank, where the expected development is to take place, in the River Tees model will allow this simple assessment to be made. More complex 2D modelling maybe appropriate if river levels are increased with development especially if new flow paths are created. Peak levels could be used to set floor or defence levels. Teesdale 2 This site is shown to be at risk from the River Tees (fluvial) but only from the 1 in 1000 year event (Flood Zone 2). A historical flood outline also covers part of this site. The Environment Agency s historical data states that defences overtopped and flooded this area in However, the NFCDD data shows that there are no flood defences here. As this area has flooded in the past, the estimated flooding probability (1 in 1000 year) is questionable. A site specific flood risk assessment should assess the flood risk to this site in more detail. Figure 4-3: Teesdale 2 development allocation and the historic flood outline 4$6 10=> Some sites have small narrow sections within Flood Zone 3 (e.g. North Shore 1). The boundaries of these proposed development sites can easily be moved to avoid the need for further investigation or the need for the Exception Test Sites at risk from the tidal Tees The tidal Flood Zones in this area are extensive and cover large areas of low lying land. However, it must be acknowledge that the Environment Agency Flood Zones ignore defences, therefore actual risk may be significantly lower. The Flood Zones in this area is still dependent on the early flood map and has not been updated. As described in 3.2.1, a 2D TUFLOW model has been produced to better represent tidal flooding. This model has /

57 provided draft Flood Zones and climate change extents, including flood depths. For the Level 2 SFRA, it will be possible to use the model for the assessment of defence breaching or overtopping. A defence asset survey was undertaken in the Tees Tidal Strategy which would be the basis of breach or overtopping assessments, together with standard general guidance. Seal Sands, North Tees Pools, Port Clarence, Haverton Hill, North Tees Pools, Billingham Reach and Casebourne sites All of these sites are classed as less vulnerable redevelopment sites. Therefore whilst PPS25 may allow this development in Flood Zone 3, every step must be taken to reduce or remove flood risk to allow inward investment and continued regeneration. As these sites are mainly at risk from tidal flooding, mitigation could be simply floor raising. This could help reduce or fully remove risk to the development and surrounding buildings. However, if large areas of tidal floodplain were removed then this may result in general increase in extreme tidal levels. This issue should be checked by modelling within a Level 2 SFRA. It should be noted that the new 2D TUFLOW tidal model has produced draft flood outlines. This new draft modelling reduced the extent of the tidal outline. The following sites are either outside of the new extent or have had the extent reduced: Billingham Reach (1, 2 and 3). Casebourne Port Clarence Haverton Hill 1, 2, 4 North Tees Pools, still at risk but reduced Seal Sands, almost completely removed from the flood zones However, the TuFlow model will need to be further refined during the Level 2 SFRA. The above sites will therefore not be eliminated from the Level 2 SFRA at this stage, as the probability of flooding will need to be confirmed. Although likely to be no longer at risk, sites such as Port Clarence, Seal Sands and North Tees Pools have other issues such as access and egress. This is because the sites are completely surrounded by Flood Zone 2 and 3. Safety of these sites and potential mitigation methods will be assessed in the Level 2 SFRA. During the Level 2 SFRA, other flood risk information will need to be investigated in relation to these sites. There is historical tidal flooding at Port Clarence but this appears to have occured to the north of the Haverton Hill and Port Clarence proposed development sites. There is flooding information on the HBC Scrapyard (surface water pooling). This is between the Casebourne and Billingham Reach proposed development sites. The historic flooding should be taken into account when assessing these sites in a Level 2 SFRA (see section 4.3.2). There is historic flooding from gulleys next to the Chemplex sites. This should be further investigated in a site specific FRA. Tees Marshalling Yard The Tees Marshalling Yard proposed development site is shown to be within Flood Zone 2 and 3. The risk here is perceived to be a mixture of tidal (backing up of the Old River Tees from the tidal Tees) and direct fluvial risk from the Old River Tees. Housing development has been proposed on the sites therefore the Exception Test will have to be passed for areas within Zone 3. At present the Flood Zones are based on generalised modelling and were not updated in the 2008 Tees Flood Mapping Study. How the Old River Tees actually interacts with the /

58 River Tees will be the key to flood risk in the area. Currently there is no hydraulic model of the Old River Tees. A Level 1 FRA has been carried out for Tees Marshalling Yard by Hyder Consulting. However, the findings are broad scale and no hydraulic modelling has been completed. It is recommended that a more detailed FRA models the Old River Tees downstream of the A1130. This would involve surveying the watercourse and building a new 1D hydrodynamic model. In addition, a site survey should be undertaken to identify whether or not to site is a risk of tidal flooding. During this study, other flood risk information has bee collected relating to this site. The Tees Marshalling Yard has historic flood risk locations on or near to it. Surface water flooding has occurred on the roadway to the south of the site. There is also historical tidal flooding on this site (1953 event). Localised flooding has occurred southeast of the site at the Aintree Oval. In addition, a thunderstorm also caused localised flooding at the Teesside Retail Park, just south of this site. These historic flooding locations should be taken into account when assessing the Tees Marshalling Yard in a Level 2 SFRA. Figure 4-4 shows Flood Zone 2 (light blue) and Flood Zone 3 (dark blue) with the historic flooding locations. The proposed future allocations are outlined in red. Figure 4-4: Tees Marshalling Yard allocation with Flood Zones and historic flooding locations Surface water flood risk 4$6 10=> A number of proposed development sites at risk from surface water flooding. Some of the sites are situated directly on surface water flow paths. Large dense development could have significant implications on current risk in the area and further downstream if runoff is not controlled. Whilst surface water vulnerability zones are not specifically included within /

59 the Sequential Test, it is recommended in this SFRA that the suite of SFRA maps produced should be used to carry out a sieving process to development sites identified at risk. Those sites situated on immediate flow paths should be removed or surface water considered during master planning of the site itself. An example is the Tees Marshalling Yard site, shown in Figure 4.5 below. This shows the surface water map in blue and the proposed development allocations in black outline. From the surface water mapping, it seems that the railway lines currently provide a surface water flow pathway. Sites like this should either be removed from development, go through the Sequential Test sieving process or have surface water management as a constraint to development. Figure 4-5: Surface Water Map at Tees Marshalling Yard Site 4$6 10=> Table 4-3 shows the larger proposed development sites that have a high percentage of surface water flooding vulnerability. However, the majority of the sites are at risk from low probability surface water flooding with a much smaller area of the sites at risk from intermediate and high probability surface water flooding. These sites should consider surface water management as an essential part of the development proposals possibly through a surface water management strategy. /1