Flood Risk Assessment for Residential and Industrial Developement at Aston Timber Yard, Sedge Fen, Lakenheath
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FLOOD RISK ASSESSMENT FOR RESIDENTIAL AND INDUSTRIAL DEVELOPEMENT AT ASTON TIMBER YARD, SEDGE FEN, LAKENHEATH FINAL REPORT ECL0407/ACORUS RURAL PROPERTY SERVICES DATE JANUARY 2021 ELLINGHAM CONSULTING LTD Email: [email protected] DISCLAIMER This document has been prepared solely as a Flood Risk Assessment in support of a planning application for a proposed residential and commercial development at Sedge Fen, Lakenheath. “Ellingham Consulting Ltd” accepts no responsibility or liability whatsoever for any use made of this document other than by the client “Mr B Rutterford” for the purposes it was originally commissioned and prepared. All comments and opinions made are based upon information available to “Ellingham Consulting Ltd” during the necessary investigative process, and the conclusions and recommendations could, therefore, differ in the event of material subsequently being found erroneous, incomplete, or misleading. “Ellingham Consulting Ltd” therefore, accepts no liability should this prove to be the case. CONTENTS 1.0 INTRODUCTION 2.0 SITE LOCATION AND DESCRIPTION 2.1 Site Location 2.2 Existing Site 2.3 Proposed Development 2.4 Local Development Documents 2.5 Available Flood Risk Information 3.0 FLOOD RISK VULNERABILITY 3.1 The Sequential and Exception Test 3.2 Vulnerability Classification 3.3 Application of the Sequential Test 4.0 SITE SPECIFIC FLOOD RISK 4.1 Local Flood Assets 4.2 Sources of Flooding 4.3 Probability of Flooding 4.4 Historic Flooding 4.5 Climate Change and Residual Risk 5.0 FLOOD RISK MITIGATION 5.1 Summary of Risks 5.2 Mitigation Measures 5.3 Surface Water Management 6.0 CONCLUSIONS AND RECOMMENDATIONS ATTACHMENT 1 – Site Location and Block Plan (Dwg RUTTERFORD S1 20-01) ATTACHMENT 2 – Environment Agency Flood Risk Information ECL0407 Ellingham Consulting 1.0 INTRODUCTION This Flood Risk Assessment has been prepared in accordance with National Planning Policy Framework (NPPF) and supporting planning practice guidance (PPG) on Flood Risk and Coastal Change. In areas at risk of flooding or for sites of 1 hectare or more, developers are required to undertake a site-specific Flood Risk Assessment to accompany an application for planning permission. This Flood Risk Assessment has been produced on behalf of Mr B Rutterford in respect of a development that consists of two residential dwellings and two industrial units at Aston Timber Yard, Sedge Fen, Lakenheath. A planning application for the proposed development is to be submitted by Acorus Rural Property Services. 1 ECL0407 Ellingham Consulting 2.0 SITE LOCATION AND DESCRIPTION 2.1 Site Location The site is situated at Aston Timber Yard, Sedgefen Road, Sedge Fen, Lakenheath, IP27 9LQ. The National Grid Reference of the site is 56637/28446. The location of the site is shown on Figure 1. Site Location Figure 1 – Location Plan (© OpenStreetMap contributors) 2.2 Existing Site The site is a timber yard on the northern side of Sedgefen Road in the village of Sedge Fen. The building within the site was destroyed by fire in 2019. There are agricultural buildings to the east and west of the site and agricultural land to the north. The area of development is approximately 0.70 hectares. Environment Agency LIDAR information shows that ground levels within the site are typically between +0.8m OD and +0.4m OD with the highest levels in the southern part of the site and the lowest levels along the northern boundary. The carriageway level of Sedgefen Road alongside the site is +0.9m OD. The agricultural land to the north of the site is below datum. The site is in the Burnt Fen Internal Drainage Board’s (IDB) area. Surface water at the site drains naturally through soakaway and hence to the IDB drain system. There is a riparian drain 200m north of the site and an IDB main drain approximately 400m east of the site. The online British Geological Survey maps indicate that the site is likely to be underlain by Gault Formation mudstone. The bedrock is shown to be overlain with superficial deposits of Alluvium (silt and clay). 2 ECL0407 Ellingham Consulting 2.3 Proposed Development The proposed development consists of two residential dwellings and two industrial units to accompany the dwellings. The dwellings will have two storeys. The existing building at the site will be demolished. A Site Plan is provided in Attachment 1. 2.4 Local Development Documents The Forest Heath Core Strategy Development Plan 2001-2026 adopted May 2010 provides the overall vision for the former Forest Heath District Council area. West Suffolk have commenced a review of the local plan which will set out the long term planning and land use policies for the area. A Level 2 Strategic Flood Risk Assessment (SFRA) for the former Forest Heath District Council area was prepared in 2011. The Suffolk Lead Local Flood Authority (LLFA) is a statutory consultee for surface drainage proposals for major developments. The Suffolk Flood Risk Management Partnership, which is made up of all the relevant Risk Management Authorities relevant to flood risk in Suffolk, have produced the Suffolk Flood Risk Management Strategy which is a tool to understand and manage flood risk. 2.5 Available Flood Risk Information The site is located within Flood Zone 3, an area with a high probability of flooding benefitting from defences, of the Environment Agency Flood Maps for Planning as shown in Figure 2. Figure 2 – Environment Agency Flood Map for Planning 3 ECL0407 Ellingham Consulting The Environment Agency Long Term Flood Risk Maps show that: • the site has a low risk of flooding from rivers (annual probability between 0.1% and 1.0%); • the site has a very low risk of surface water flooding (annual probability less than 0.1%); and • the site is not within an area at risk of reservoir flooding. Flood risk information provided by the Environment Agency for a nearby site is provided within Attachment 2. 4 ECL0407 Ellingham Consulting 3.0 FLOOD RISK VULNERABILITY 3.1 The Sequential and Exception Test The NPPF requires the application of a Sequential Test to ensure that new development is in areas with the lowest probability of flooding. The Exception Test is a method to demonstrate and help ensure that flood risk to people and property will be managed, while allowing necessary development to go ahead in situations where suitable sites at lower risk of flooding are not available. 3.2 Vulnerability Classification Table 2 of the PPG Flood Risk and Coastal Change categorises different types of uses and development according to their vulnerability to flood risk. The proposed develop includes residential dwellings and is therefore classified as ‘More Vulnerable’. Table 3 of the PPG Flood Risk and Coastal Change sets out Flood Risk Vulnerability and flood zone ‘compatibility’. The site is in Flood Zone 3 and the development is ‘More Vulnerable’ therefore it is necessary to complete the Exception Test. PPG Flood Risk and Coastal Change defines that the lifetime of the development in terms of flood risk and coastal change is 100 years. 3.3 Application of the Sequential and Exception Test It is for the Local Planning Authority, taking advice from the Environment Agency as appropriate, to consider the Sequential Test. Large parts of West Suffolk to the west of Lakenheath and Mildenhall are within Flood Zone 3. The defences along the Little Ouse River were not considered during the preparation of the Environment Agency Flood Maps. When the level of protection provided by the defences alongside the Little Ouse River is considered the site has a low risk of flooding. Consequently, alternative sites in Flood Zone 1 could not be considered to have a lower level of risk. As such the site is considered to pass the Sequential Test. The Exception Test requires consideration of the wider sustainability benefits of a development and that the development would be safe and residual risks managed. The Core Strategy Policy CS7 for Housing defines the housing need and distribution for new dwellings across the district. It estimates that 340 new homes a year are required over the period 2011 and 2031. The proposed development will contribute to this target and the provision of rural housing is considered to provide a sustainability benefit. In addition, the industrial units will support the local economy. Section 5 of this Flood Risk Assessment describes the flood mitigation measures and the management of the residual risks, demonstrating that this development will be 5 ECL0407 Ellingham Consulting safe and not increase flood risk elsewhere. The development is considered to pass the Exception Test. 6 ECL0407 Ellingham Consulting 4.0 SITE SPECIFIC FLOOD RISK 4.1 Local Flood Assets The site is approximately 1.3km south west of the Little Ouse River. The Little Ouse River is an embanked main river. The Little Ouse has its confluence with the River Ely Ouse approximately 8km downstream of the site. Both the River Ely Ouse and the Little Ouse River are the responsibility of the Environment Agency. There is a long-term strategy for the maintenance of the Environment Agency defences which is reviewed and updated every 5 years. There is an extensive local drainage network managed by the Burnt Fen Internal Drainage Board. There is an IDB main drain approximately 400m east of the site. The site, and surrounding land, drains by gravity to Lark Pumping Station to discharge into the River Lark. The River Lark is also a tributary of the River Ely Ouse. During the operation and maintenance of its pumping stations, associated structures, and channel systems, the IDB seeks to maintain a general standard capable of providing flood protection to its district. A routine maintenance programme is in place to ensure that the Board’s assets are commensurate with the standard of protection that is sought.