Flood Risk Assessment Severnside Farm, Gloucester
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Flood Risk Assessment Severnside Farm, Gloucester Date 15/12/2016 Prepared by Abi Hall Prepared by Abi Hall..………………………….. 15/12/2016 Date …………………………………….. Version ……………………………………..1.0 Reviewed by Katherine Teakle.……………….. 15/12/2016 Date …………………………………….. Version ……………………………………..1.0 i Table of Contents 1.0 INTRODUCTION .................................................................................................1 1.1 Introduction ............................................................................................................1 1.2 Location .................................................................................................................1 1.3 Aims and Objectives...............................................................................................3 2.0 DEVELOPMENT DESCRIPTION AND BACKGROUND.....................................4 2.1 Development Site Description.................................................................................4 2.2 National Planning Policy Framework (NPPF) ..........................................................4 2.3 Development Site Background................................................................................5 3.0 FLOOD HAZARD DEFINITION AND PROBABILITY .......................................10 3.1 Fluvial and Tidal Sources .....................................................................................10 4.0 CONCLUSION ..................................................................................................16 5.0 REFERENCES ..................................................................................................18 APPENDICES...............................................................................................................19 APPENDIX A............................................................................................................................20 APPENDIX B............................................................................................................................24 ii Blank Page iii Flood Risk Assessment Severnside Farm, Gloucester 1.0 Introduction 1.1 Introduction 1.1.1 Katherine Colby Hydrologists Limited has been commissioned by Mr. Gorman to undertake a Flood Risk Assessment of Severnside Farm, Gloucester. A Flood Risk Assessment is required to support a Retrospective Planning Application for the development of an agricultural barn building. 1.1.2 The barn building has already been built on the east of the site, on the north side of an access road; there is also a farmhouse in this location, situated south of the barn. The site is accessed by a private drive from Longhorn Avenue. 1.2 Location 1.2.1 The site is located in Gloucester, which is south of Worcester, north east of Bristol, north west of Oxford and south east of Hereford (Figure 1). 1.2.2 Specifically, the site is located to the north-west of Gloucester, south of the A40 (Figure 2). To the south-east of the site is St Oswalds Retail Park and to the south of the site is the Cattle Market housing development. The River Severn runs along the western boundary of the site and the River Twyver runs along the southern boundary of the site. 1.2.3 A National Grid Reference for the site is 382800, 219760 and a post code is GL2 9NF. 1 Flood Risk Assessment Severnside Farm, Gloucester Figure 1: Site location (Nigel J Teale, 2016) 2 Flood Risk Assessment Severnside Farm, Gloucester 1.3 Aims and Objectives 1.3.1 This report aims to provide an assessment of flood risk in line with National Planning Policy Framework for the purpose of supporting a Retrospective Planning Application for an agricultural barn building. 1.3.2 The objectives of this report are to review available information about geology, topography and hydrology local to the site. Then to assess the risk of flooding from fluvial and tidal sources based on this information and consultation with relevant authorities. Recommendations will be made, where necessary, to manage and/or mitigate any flood risks identified. 3 Flood Risk Assessment Severnside Farm, Gloucester 2.0 Development Description and Background 2.0.1 The following section provides a description of the site layout (Appendix A). Background information about topography, geology and hydrology of the site and surrounding area are also detailed to provide a baseline to the Flood Risk Assessment. 2.1 Development Site Description 2.1.1 The site is currently an agricultural holding; it is occupied by agricultural buildings to the west and a farmhouse and barn to the east. 2.1.2 The development is a corrugated metal barn with an area of 244.25m2 located on the eastern part of the site. There is existing vehicular access via a private driveway from Longhorn Avenue. The barn is built on a raised area on the north side of an access road, which is also raised. The agricultural barn has been built to the north of the existing farmhouse. 2.1.3 The majority of the land at Severnside Farm is currently rough grassland with trees and hedgerows creating boundaries between fields and as a site boundary. The land is used for grazing in places; however some of the land is marshy. 2.1.4 To the north of the site is the A40, the Gloucester Northern Bypass. St Oswalds Retail Park and the Cattle Market housing development are located to the south of the site. The site is located with the River Severn flowing along the western boundary and the River Twyver flowing along the southern boundary. The confluence of these two rivers occurs at the south west corner of the site. 2.1.5 The proposed development is for agricultural use. Therefore, in line with the Planning Practice Guidance to the National Planning Policy Framework, it is considered that the building would be classified as “Less Vulnerable”, based on the flood risk vulnerability classification outlined in Table 2 of the National Planning Policy Framework (Communities and Local Government, 2014). 2.2 National Planning Policy Framework (NPPF) 2.2.1 Sequential and Exception Tests 2.2.2 The land at Severnside Farm, Gloucester is shown to be located within Flood Zone 3 on the Environment Agency’s Indicative Flood Zone Map (Figure 5). The Environment Agency’s Indicative Flood Zone Map illustrates the risk of flooding without flood defences in place. 2.2.3 Table 3 in NPPF provides a matrix of “Flood Risk Vulnerability and Flood Zone ‘Compatibility’” (Communities and Local Government, 2012). The site is located in Flood Zone 3. As discussed above the Flood Risk Vulnerability Classification of the development is “Less Vulnerable”. Therefore, based on Table 3 in NPPF, the proposed development is considered as “appropriate” for development in Flood Zone 3. 4 Flood Risk Assessment Severnside Farm, Gloucester 2.3 Development Site Background 2.3.1 Topography 2.3.2 The site is currently an agricultural holding; it is occupied by agricultural buildings to the west and a farmhouse and barn to the east. The agricultural barn building in question is located on the east part of the site, near the farmhouse and has already been developed. 2.3.3 A topographic survey of the site Severnside Farm, Gloucester has been undertaken by Ruxton Surveys in October 2016; this has been reviewed and is discussed below (Figure 2). 2.3.4 The barn is built on the north side of an access road at the site, on an area that is raised above surrounding site levels. At the barn elevations range from 11.13mAOD to 10.87mAOD and the barn has a floor level of 10.92mAOD (Figure 2). There is a low point of 10.55mAOD on the raised area, to the north west of the barn building (Figure 2). 2.3.5 Land levels decrease relatively steeply down from the raised area, upon which the barn and the access road are located, with the difference in elevation between the top edge of the raised area and the base of the raised area in the vicinity of the barn being between about 1.86m and 2.01m on the north side of the barn and between about 1.65m and 2.24m on the south side of the access road (Figure 2). 2.3.6 The high point in the vicinity of the building is on the access road, south of the barn, where elevations rise to 11.17mAOD (Figure 2). There is also an area of raised land west of the barn where elevations rise to 11.42mAOD (Figure 2). 2.3.7 There is an overall increase in elevations along the access road to the site from east to west travelling into the site; elevations increase along the track from approximately 11.00mAOD at the entrance to the site, rising to 11.13mAOD near the barn (Figure 2). The access road is described as a “stone track” in the topographic survey and as such it is an uneven surface, with a low of 10.83mAOD (Figure 2). It is noted that this low elevation occurs on the north side of the access road and on the south side levels of 10.92mAOD and 10.95mAOD are recorded in this location on the access road (Figure 2). 5 Flood Risk Assessment Severnside Farm, Gloucester Figure 2: Topographic Survey (Nigel Teal, 2016) 6 Flood Risk Assessment Severnside Farm, Gloucester 2.3.8 Geology 2.3.9 Available mapping for the area of interest was reviewed, namely the British Geological Survey (1975) Gloucester, England and Wales Sheet 234, Solid and Drift Geology 1:50,000. This map indicates that the site is underlain by “Estuarine Alluvium” (British Geological Survey, 1975). 2.3.10 The Environment Agency in their letter dated 18th November 2016 (Appendix B) stated that there are “no groundwater level observational boreholes in this location”. 2.3.11 Hydrology 2.3.12 The River Severn flows in an overall north to south direction around