Flood Risk Assessment Proposed Development Site Mytholme House Waterfoot Rossendale
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FLOOD RISK ASSESSMENT PROPOSED DEVELOPMENT SITE MYTHOLME HOUSE WATERFOOT ROSSENDALE Carley Daines & Partners 11, Bridgewater Road Walkden, Worsley 12-B-10063 Manchester M28 3JE email:- [email protected] 14th May 2013 CONTENTS 1 Introduction & Objectives 2. Site Location & Description 3. Appraisal of Flood Risk – on site 4. Appraisal of Flood Risk – off site 5. Conclusions & Recommendations 6. Appendices 1.0 INTRODUCTION 1.1 This report has been produced following a study of relevant information, and the obtaining of flood data from Envirocheck and the Environment Agency, as well as site visits. 1.2 This Flood Risk Assessment is based upon the requirements of the Communities and Local Government Department Document – Planning Policy Statement (PPS) 25:Development and Flood Risk. 1.3 PPS25 maintains the classifications of Flood Zones 1, 2 and 3. Flood Zone 3 is sub-divided to Flood Zones 3A (high probability) and Zone 3B (functional flood plain). 1.4 PPS25 also introduces a flood risk classification of development to essential infrastructure, highly vulnerable, more vulnerable, less vulnerable, and water compatible development. Residential dwellings are generally identified as being in the more vulnerable category, whilst commercial/retail development is generally defined as being less vulnerable. 1.5 Annex C of PPS25 indicates that flooding from the following sources should be considered to develop a full risk assessment: - Rivers - Sea - Land - Ground water - Sewers - Reservoirs, canals and other artificial sources. 2.0 SITE LOCATION AND DESCRIPTION 2.1 The site is located close to Waterfoot Town Centre, to the east of Burnley Road East and to the south of Wood Lea Road. The site is just to the north of a car park accessed from Bacup Road. The site post code is BB4 9AJ. 2.2 The site is irregular in shape, and is presently developed. The principal development is a building, now disused, named Mytholme House. The site is reasonably level at an altitude of 197m above sea level. Much of the site is covered with hardstanding, comprising car parking and a children's playground. -2- 2.3 The site grid reference is NGR383450,421870. 2.4 The site area is 3,200m2 (0.32 hectares). 2.5 There are no watercourses on site. However, the north west boundary is formed by the southern bank of Whitewell Brook. This is designated as a Primary River. Furthermore, the River Irwell is located approximately 150m to the south, and both Cowpe Brook and Whitewell Brook have a confluence with the River Irwell, close to Waterfoot Town Centre. All three watercourses are designated as Primary Rivers. These watercourses ultimately form part of the Mersey Drainage Basin. 2.6 The site appears to be reasonably level, and the principal building on site is a disused building (formerly flats) which presently awaits demolition. This appears to date from the late 1970's or early 1980's. 2.7 The proposed development assumes the construction of a three storey building with associated drainage and parking infrastructure. Precise details are not presently known, though it is believed that the development will contain new flats. 3.0 APPRAISAL OF FLOOD RISK – ON SITE 3.1 Flood data for the site has been obtained at scales of 1:10,000 & 1:50,000 (see Appendix). 3.2 The data also indicates areas prone to flooding under extreme storm conditions for 75 year, 100 year & 1000 year return periods. 3.3 No enhancement is indicated on the plans for climate change allowance. However, it is generally accepted good practice that flood levels projected forward by 50 years should be enhanced by 200mm (0.2m). 3.4 The Online Environment Agency Flood Map indicates that the site falls within Flood Zone 1. However, the site is on the edge of an extreme event flood zone, and much of Waterfoot Town Centre is defined as being within Flood Zone 2. Flood Zone 1 is defined in PPS25 as land having a less than 1 in 1000 annual probability of flooding. 3.5 Detailed Environment Agency Flood Maps & data also indicate the site as being in Flood Zone 1, even though located directly adjacent to Whitewell Brook. -3- 3.6 The 75 year, 100 year and 1000 year return flood maps indicate the site as being at risk from extreme pluvial flooding. 3.7 Local enquiries indicate that Waterfoot Town Centre has not been subject to historic flooding. Indeed, other reports indicate that Waterfoot has been constructed on made ground and levels raised above the maximum flood levels of the local rivers. 3.8 Envirocheck Historic Flood Events indicate that flooding did occur in both 2002 & 2004, the closest of which was over 650m from the site. 3.9 Insurance enquiries indicate that the post code BB4 9—has a low to very low flood insurance claim rating. 4.0 APPRAISAL OF FLOOD RISK – OFF SITE 4.1 In this respect, consideration is given to the effect of the proposed development on the surrounding areas. 4.2 It is considered that the proposed development will have no effect whatsoever on the immediate locality, and does not in any way increase flood risk. This is because of the following factors: - The new building will be similar in scale and size to the existing. - The surface water run off regime will exactly replicate the existing. - There will be no increase in impermeable area on the site, and in all probability impermeable area will be reduced. - The proposed development is very small, and is insignificant in the context of the wider area. 5.0 CONCLUSIONS 5.1 This Flood Risk Assessment has obviously principally concentrated upon the possibility of flooding from rivers and watercourses. -4- 5.2 In view of the close proximity of the site to Whitewell Brook and the River Irwell, this is a justifiable approach. 5.3 From this review, it would appear that the site is sufficiently elevated above Whitewell Brook. The possibility of river flooding can therefore be regarded as being negligible. 5.4 However, in our opinion, it would be appropriate if additional precautions were taken by ensuring that the lowest ground floor levels of the proposed units are constructed at a height of 200mm above floor level of the existing building, which is scheduled for demolition. This will take into account any possible increase in flood levels due to climate change. 5.5 As indicated above, PPS25 also requires an assessment of flooding from all potential sources. These are assessed as follows: Flooding from the sea – risk – zero. The site is at a level of 197m AOD, and at a closest distance of approximately 50km from the coast line. Flooding from land – risk - negligible – there is no recorded overland flow path of flood water and no evidence to suggest that has ever occurred in the past or will occur in the future. Flooding from ground water – risk negligible to low – there are no recorded instances of ground water flooding, and hydro geological data indicates a permeable sub-strata with a secondary aquifer below. Flooding from sewers – risk – low. We understand that sewers in the area have ample capacity to cope with surface water discharge, generally discharging directly to the Primary Rivers. Flooding from artificial sources – risk - zero to negligible. There are no artificial water features considered to pose a risk to the proposed site development. -5- 5.6 On balance therefore, and not withstanding any other planning considerations, we do not believe that there any flood related issues that are likely to have a negative impact on the proposed development, subject to a consideration of exact finish floor levels as outlined above. It is therefore our opinion the site should be considered to be entirely suitable for the proposed development from a flood risk point of view. SIGNED C.R. CARLEY CARLEY DAINES & PARTNERS A P P E N D I X 1:1000 & 1:50,000 FLOOD MAPS & FLOOD DATA .