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Policy ENV7: Flood Risk and Drainage

1. Development at an unacceptable risk of flooding will not be permitted. Where a development would be within an area of flood risk, the applicant will be required to: a) submit evidence to establish that the development could not be practicably located within an area of lower or no flood risk. b) submit a flood risk assessment, which will fully assess the risks of flooding associated with the development in accordance with the requirements of Planning Policy Guidance note 25 "Development and Flood Risk". 2. Development will not be permitted if it may cause an unacceptable risk of flooding elsewhere. 3. Mitigation measures will be required, where necessary, to manage flood risk associated with or caused by new development. These should; a) Be derived from a flood risk assessment; b) Be fully described in the planning application; c) Be fully funded - including for the provision of long-term maintenance - as part of the development; and d) Contribute to the biodiversity resource of the Borough. 4. New development will not be permitted unless a Sustainable Drainage System is incorporated into the overall design. Exceptions may be made where it can be demonstrated that: a) The Sustainable Drainage System would be likely to cause either significant land or water pollution; or b) The site’s ground conditions would preclude the use of a Sustainable Drainage System; or c) The size of the site precludes the use of a Sustainable Drainage System; or d) The proposed Sustainable Drainage System could cause damage to adjacent buildings or sites.

*Explanation ENV7* 13.33 It is recognised by the Council that flood risk is likely to increase as a result of climate change. Planning Policy Guidance Note 25 “Development and Flood Risk” requires new development to be consistent with the sustainable management of river systems. Within Knowsley this means having regard to Merseyside-wide initiatives including the Mersey Basin Campaign and the Alt/Crossens Action Plan 2000+. 13.34 The areas currently identified as being at risk from flooding within Knowsley are within the catchment of the River Alt in the northern part of the Borough and Ditton Brook to the south. These areas are based upon the most up to date data from the Environment Agency. Policy ENV7 requires proposals for new development (other than for very minor development such as small extensions and alterations) that are to be located in an area of flood risk to be accompanied by evidence to establish that there are no areas of lower or no flood risk available for that development. 13.35 The policy also imposes controls over new development which may itself increase flooding elsewhere by increasing surface run-off, thereby over stretching the capacity of watercourses and sewers. To control run off as close to the source as possible, the use of Sustainable Drainage systems (SuDs) is often appropriate. These represent a move away from traditional piped drainage systems to those that mimic natural drainage processes e.g. balancing ponds and infiltration devices. 13.36 Part 4) of this policy aims to complement Part H of the Building Regulations 2000 by ensuring that SuDS are incorporated into the overall design of the development. The policy will apply to developments comprising one dwelling or more and also to applications for new retail, industrial and warehousing, as well as commercial uses such as hotels. 13.37 SuDS may be inappropriate in areas which comprise soils with low infiltration rates or where there may be an increased risk of polluting land or water. For example, SuDS may not be suitable for use on contaminated sites or where industrial development is proposed that uses or stores hazardous materials. It will be the responsibility of the applicant to demonstrate why it may be inappropriate to incorporate SuDS into the overall design of their scheme. Whilst secondary benefits such as the creation of new biodiversity habitats are to be welcomed, the primary functions of SuDS must take priority. Procedures 13.38 A flood risk/run-off assessment will be required as part of the planning application for any development which is likely to cause or be subject to a risk of flooding. The Council will adopt a Supplementary Planning Document which will describe where the areas of flood risk are, using the most up to date copy of the Environment Agency’s flood zone maps and to explain the other requirements of this policy further. Merseyside-wide planning guidance is currently being prepared for SuDs to provide more detailed guidance including cross boundary flooding and drainage issues. 13.39 Planning conditions or legal agreements will be used to ensure that where appropriate Sustainable Drainage Systems are provided and maintained. Next



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