Level 2 Strategic Flood Risk Assessment: Volume 3 Southampton Key Development Sites Flood Risk Management Options and Feasibility Study
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Level 2 Strategic Flood Risk Assessment: Volume 3 Southampton Key Development Sites Flood Risk Management Options and Feasibility Study August 2010 Southampton Level 2 SFRA: Volume 3 Southampton City Council Strategic Flood Risk Assessment: Volume 3 Report REV 2.0 / August 2010 This document is the property of the Southampton City Council. If you have received it in error, please return it immediately to the above named Local Authority. Job Number: CS/038822 PD: James Reddish PM: Paul Hlinovsky Report status: REV 2.0 Date of issue: August 2010 CSL Main author(s): Paul Hlinovsky CSL Checked: James Reddish Client Approval: Rob Crighton (SCC) This report has been prepared by Capita Symonds Limited with all reasonable skill, care and diligence within the terms of the Contract with the Client, incorporating our General Terms and Conditions of Business and taking account of the resources devoted to it by agreement with the client. We disclaim any responsibility to the client and others in respect of any matters outside the scope of the above. This report is confidential to the client and we accept no responsibility of whatsoever nature to third parties to whom this report, or any part thereof, is made known. Any such party relies on the report at their own risk Southampton City Council i August 2010 Southampton Level 2 SFRA: Volume 3 PREFACE It is accepted that the technical content of the Southampton SFRA will need to be reviewed and amended as new information becomes available. The policy basis for this version is PPS 25 (CLG, March 2010) and the PPS 25 Practice Guide (CLG, December 2009). Although there is no statutory consultation requirement at this stage, the nature of the intended end use for the information makes it appropriate to obtain feedback relating to the report in order to contribute to the overall robustness and credibility of this work. This information will also be an aid when formulating the necessary next steps in engaging those parties who will be involved in the future. It is the responsibility of the reader to be satisfied that they are using the most up to date information and that this has been included within the Southampton SFRA. Southampton City Council ii August 2010 Southampton Level 2 SFRA: Volume 3 FOREWORD The South East Plan promotes major development growth in South Hampshire. A Strategic Flood Risk Assessment (SFRA) has been completed by the Partnership for Urban South Hampshire (PUSH) which provides information on flood risk, taking account of climate change to provide a greater understanding of the risks across the sub-region and individual local authority area to allow the appropriate application of the Sequential Test. The City Council Core Strategy was submitted in July 2009 and adopted in January 2010. In compliance with the South East Plan, it proposes major new development within the city (approximately 16,300 dwellings, a minimum of 130,000 square metres of retailing floor space, and 322,000 square metres of office floor space). The office and retail development, along with approximately 5,500 dwellings, will be located within the city centre. A significant element of the city’s development targets will need to be delivered in areas at risk of flooding, particularly on development sites in the central area, such as the major development quarter in the west of the city centre. Core Strategy Policy CS23 sets a strategic approach to flood risk and the need for further assessment (with reference to the Core Strategy’s flood risk background paper). The Council is now in the process of preparing two subsequent “allocation plans” to identify specific development sites: the City Centre Action Plan and the Sites and Policies Plan (for the balance of the city). The further assessment of flood risk required to inform these plans are detailed in this scope. It is currently estimated that these action plans will be adopted in January 2013. Strategic Aims and Objectives The Practice Guide (CLG, December 2009) identifies a strategic approach to the preparation of SFRAs so that the level of details of assessment matches the significance of the risk. This SFRA describes the outcome of a ‘Level 2’ assessment, in accordance with paragraph E6 of PPS 25 and Section 3.59 of the PPS 25 Practice Guide. It contains a general assessment of risk from all sources over the whole study area and also detailed analysis for locations where flood risk is a significant issue (i.e. key development sites). The principle objective of the Level 2 SFRA is to provide the appropriate level of information to facilitate the application of the Sequential and Exception Tests for development within the city of Southampton. More detailed information is required where there is deemed to be development pressure in areas that are at medium or high probability of flooding and where there are no other suitable alternative areas for development after applying the Sequential Test. This more detailed study considers the detailed nature of the flood hazard, taking account of the presence of flood risk management measures. This will allow a sequential approach to site allocation to be adopted within a Flood Zone (paragraphs 17 and D4 of PPS25), taking into consideration the wider planning context of Southampton. It will also provide a level of detail suitable for informing part C of the Exception Test at the ‘local’ scale, and informs the relevant Local Development Documents of the Local Development Framework. Southampton City Council iii August 2010 Southampton Level 2 SFRA: Volume 3 The aims of this Level 2 SFRA are to: a) Inform policies and plans to ensure future developments, where appropriate, have been subjected rigorously to the applications of the Sequential and Exception Tests, satisfying PPS 25; b) Identify strategies to limit flood risks and adapt to climate change; and c) Ensure the safety of new development. The Level 2 SFRA has been provided as three distinct ‘volumes’: Stage 1: o Volume 1 – Strategic Assessment: the preparation of baseline information on flood risk, including guidance on using the SFRA and recommendations on policy development; o Volume 2 – Technical Appendices and Mapping; Details- how the data informing the Level 2 SFRA has been prepared; and, Stage 2: o Volume 3 – Flood Risk Mitigation Options and Feasibility Study : Building on the data in Vol. 1 and Vol. 2 to prepare conceptual measures to manage flood risk at key development sites in Southampton. This report is Volume 3 of the assessment and the report structure is shown overleaf. The SFRA is a live document that is intended to be updated as new information and guidance becomes available. The outcomes and conclusions of the SFRA may not be valid in the event of future changes to legislation, policy, revised government guidance on flood risk, the data or the baseline flooding situations. Decisions also require the inclusive assessment of wider planning issues and the user should be aware that changes to decision making principles affecting other planning issues can potentially affect the outcome of the risk based Sequential Test. The contents of this document are also dependent on the outcomes of the Regional Flood Risk appraisal. It is the responsibility of the user to ensure they are using the best available information. Southampton City Council iv August 2010 Southampton Level 2 SFRA: Volume 3 Diagram 1 – Proposed Report Structure for Level 2 SFRA Volume 1: Main body of Level 2 SFRA Report Volume 2: Technical Appendices Chapter 1 Overview: Flood Risk in Southampton Source Data Chapter 2 Applying the Sequential & Exception Tests E.g. topography Historic flood data Flood defence data, etc Chapter 3 Informing Core Strategy, City Centre Action Plan and Sites and Policies Plan Analysis E.g. flood modelling Chapter 4 Development Control: Site Specific Flood Risk Pluvial flooding Assessments assessment, etc Chapter 5 Emergency Planning Background Summary of national, Chapter 7 Flood Risk Management Measures regional flood risk policy context Chapter 8 SFRA Management and Maintenance Mapping Chapter 9 Glossary and Notation E.g. flood depth mapping Flood velocity mapping Chapter 10 References Speed of onset mapping etc Volume 3: Flood Risk Management Key Development Sites Site Proposals Site Specific Technical Assessment of Flood Risk Environmental Impacts Flood Risk Management: Economic Appraisal Strategic Precautionary Approach Site Specific Measures Managed Adaptive Approach Key Development Site Summary Southampton City Council v August 2010 Southampton Level 2 SFRA: Volume 3 CONTENTS Foreword ............................................................................................................................................... iii 1. INTRODUCTION ............................................................................................ 1-1 1.2 Assessment Methodology ...................................................................................................... 1-2 1.3 Flood Risk Management Option Assessment ...................................................................... 1-2 1.4 Environmental Impacts ........................................................................................................... 1-4 2. STRATEGIC FLOOD RISK MANAGEMENT ................................................. 2-1 2.1 Background ............................................................................................................................. 2-1 2.2 Key Strategic Flood Risk Management Assumptions ........................................................