Upper Mole Flood Alleviation Scheme Environmental Statement Volume 1 Main Text A04 Fourth Draft Final for Planning Submission: 28th January 2011 i We are The Environment Agency. It's our job to look after your environment and make it a better place - for you, and for future generations. Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier. The Environment Agency. Out there, making your environment a better place. Published by: Environment Agency Rio House Waterside Drive, Aztec West Almondsbury, Bristol BS32 4UD Tel: 0870 8506506 Email: [email protected] www.environment-agency.gov.uk © Environment Agency All rights reserved. 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Environment Agency Upper Mole FAS Environmental Statement ii Document History Record Client: Environment Agency Project: Upper Mole Flood Alleviation Project No: B1518000 Scheme Document title : Environmental Statement Ref. No. Originated by Checked by Reviewed by Approved by ORIGINAL NAME NAME NAME NAME Dave Jones James Hanson Chris Boon A01 Sarah Jennings DATE SIGNATURE SIGNATURE SIGNATURE SIGNATURE 18 November 2010 Document status REVISION NAME NAME NAME NAME James Hanson Chris Boon A02 Sarah Jennings Sophie Lee DATE SIGNATURE SIGNATURE SIGNATURE SIGNATURE 18th December 2010 Document status (3) REVISION NAME NAME NAME NAME Steve Mills Chris Boon A03 Sarah Jennings Steve Mills DATE SIGNATURE SIGNATURE SIGNATURE SIGNATURE 14th January 2011 Document status (3) REVISION NAME NAME NAME NAME Steve Mills Chris Boon A04 Sarah Jennings Steve Mills DATE SIGNATURE SIGNATURE SIGNATURE SIGNATURE 28th January 2011 Document status (3) Environment Agency Upper Mole FAS Environmental Statement iii Non Technical Summary Introduction and Background This Environmental Statement has been prepared to consider the effects that the Upper Mole Flood Alleviation Scheme might have on the environment. It is a requirement of UK law to carry out such an assessment, where there are likely to be impacts on the environment. The report is important to help the local councils and other interested parties, including the general public, understand where there might be impacts and how we propose to deal with them. Crawley suffers from flooding from the upper reaches of the River Mole, including the Gatwick Stream, Tilgate Stream, Crawters Brook and Ifield Brook. This affects both residential areas and Gatwick Airport. There were major flood events in 1968 and 2000 and smaller floods in other years. We (the Environment Agency) are proposing to build new flood detention reservoirs to reduce the flood risk in these areas. The scheme started with the raising of Tilgate Dam, which was the subject of a separate environmental assessment and is currently being constructed (completion estimated in early 2011). This scheme was started early as the dam also needed remedial works for safety reasons. We are now progressing the next phase of works, which includes: • replacement of the existing dam at Clay’s Lake with a new higher dam; • new flood detention reservoir at Worth Farm; • river restoration and environmental mitigation works in Grattons Park. A new flood detention reservoir at Ifield was also being progressed, but the planning application for this site has been postponed by the Environment Agency project board pending review of the business case. Once completed, the schemes (including the dam raising at Tilgate but excluding the potential future works at Ifield) would reduce the risk of flooding at 1038 properties in the Crawley and Horley areas, as well as to Gatwick Airport. The number of properties protected would be higher if climate change increases the risk of flooding in the future, as we expect it to. It is anticipated that the works would be carried out between 2011 and 2013 with the main period of construction anticipated during 2012. This Environmental Statement considers the proposed works at all three of the locations noted above and accompanies planning applications to the relevant local authorities. For more details or to comment on any of the applications, please contact the local authority for the scheme of interest: Worth Farm Clay’s Lake Grattons Park Stuart Malcolm Stuart Malcolm Paul Fairham Mid Sussex District Council Mid Sussex District Council Crawley Borough Council The following pages detail the scheme proposals for each site, along with the key impacts and proposed mitigation measures. Environment Agency Upper Mole FAS Environmental Statement iv Worth Farm i Details of the Scheme We are planning to build a new flood detention reservoir in agricultural land to the east of Crawley, close to the M23 motorway. There are no existing flood defences at the site. We would build a new embankment dam to a height of 6.5 metres above the surrounding ground, broadly parallel with the M23 motorway. No water would be stored in the reservoir for most of the year and the area could still be used for farming. However, during times of high river flows, water in the brook that would ordinarily run beneath the dam would start to pond up, creating a reservoir. The water would stay within the reservoir for a period of a few days before emptying again as water levels in the river fall. Water would be released at a steady rate so as not to cause flooding downstream. Once the scheme is complete, the water level is likely to rise up to 3.5 metres above existing bank level on average once every five years (20% annual chance), whilst the annual chance of the reservoir filling to its maximum capacity of 6.5 metres above existing bank level is 1 in 200 (0.5% annual chance). During large floods, the water could flood surrounding agricultural land and areas of trees. Once the flood waters recede, the area would return to normal. Building the new dam requires a supply of earth and rock, and we are intending to dig some of this from the ground in an area known as a “borrow pit”. We can get this material from the surrounding land within the reservoir footprint and we are proposing to dig into the area of low quality grazing land to the south of the stream to provide this. The remainder of the general fill material will be brought to the site by lorry. Once the works are complete, the borrow area would be restored to create woodland Biodiversity Action Plan (BAP) habitats, improving the diversity of habitats in the area. We are likely to start some early works on site during 2011, including stockpiling of fill materials, with the main works starting in early 2012 and lasting for about a year. Having the scheme in place would contribute to provision of flood protection to 1038 properties in the Crawley and Horley areas, as well as at Gatwick Airport. This would minimise the safety and health problems that are associated with flooding such as people being hit by debris in the floodwaters or having to live in damp houses, as well as the real risk to life. It would also reduce the stress people have, wondering if they will be flooded at times of high rainfall. ii The Existing Environment The Worth Farm site lies within Mid Sussex District, to the east of Crawley. The land is currently agricultural and lies within the High Weald Area of Outstanding Natural Beauty (AONB). The landscape is of high quality and there are areas of ancient woodland along the stream and in surrounding areas. The site lies hard up against the M23 motorway, which forms the western boundary of the site, with more continuous woodland to the east. The only public views of the site are from the Worth Way footpath to the north as it crosses the M23 and from the M23 itself. The Gatwick Stream runs through the site. This has populations of coarse fish with the dominant species being bullhead. Other species found include brook lamprey and brown trout. The steam also supports a range of invertebrate species. We have done surveys of the wildlife in the area and found that there are small populations of slow- worms, grass snakes and common lizards in areas of rough grassland such as the motorway verge.