Policy ENV 16: Surface water management and flood risk
In order to manage surface water drainage effectively and reduce the risk of flooding elsewhere, in accordance with LPS Policy SE 13 ‘Flood risk and water management’, development proposals should satisfy the following criteria:
- It should be demonstrated how surface water runoff can be appropriately managed. Surface water runoff should be managed to achieve:
- on greenfield sites, at least no increase in runoff rates, and a reduction in rates where possible; and
- on previously developed sites, a reduction in existing runoff rates in line with the Non-Statutory Technical Standards for Sustainable Drainage Systems (2015) or any subsequent replacement standards.
- Development proposals should manage and discharge surface water through a sustainable drainage system (SuDS). The preference will be for new development to incorporate surface level SuDS with multi-functional benefits, as opposed to underground tanked storage systems, for the management of surface water. If it is demonstrated that such a system cannot feasibly be achieved, then the following options may be implemented, in the priority listed:
- an attenuated discharge to watercourse; or
- where (i) is demonstrated not to be feasible, an attenuated discharge to a highway drain footnote 10 or public surface water sewer; or
- where (ii) is demonstrated not to be feasible, an attenuated discharge to a public combined sewer.
- Approved development proposals will be expected to be supplemented by appropriate maintenance and management regimes for surface water drainage schemes.
- Development in a critical drainage area must address and mitigate known risks in that area, where relevant and appropriate.
- Development proposals should not result in the loss of open watercourse, and culverts should be opened wherever possible. The culverting of existing open watercourses will not be permitted unless it is adequately demonstrated that there is an overriding need to do so.
- Watercourses and riverside habitats must be conserved and enhanced, where necessary, through management and mitigation measures.
4.95 LPS Policy SE 13 ‘Flood risk and water management’ seeks to reduce flood risk in the borough, through directing development to those areas that are at lowest risk of flooding from all potential sources (sequential approach). In line with the requirements of the NPPF, in the first instance development should be situated in Flood Zone 1 (low risk). Where development in Flood Zone 1 cannot be accommodated, consideration should then be made towards situating development in Flood Zone 2. Development in Flood Zone 3 should only be proposed if there are no reasonably available alternative sites (subject to the exceptions test). Inappropriate development in Flood Zone 3b will not be permitted.
4.96 There is a requirement to consult with the appropriate risk management authority (e.g. the Environment Agency), and local water companies (e.g. United Utilities) for all sources of flooding.
4.97 In demonstrating a reduction of surface water discharge on previously developed land, applicants should include clear evidence of existing positive connections from the site with associated calculations on rates of discharge. In relation to the reduction of greenfield runoff rates, applicants should include clear evidence of existing positive operational connections from the site with associated calculations on rates of discharge. This evidence is critical to make sure that development does not increase flood risk.
4.98 Landscaping proposals should consider what contribution the landscaping of a site can make to reducing surface water discharge. This can include hard and soft landscaping such as permeable surfaces to reduce the volume and rate of surface water discharge.
4.99 The treatment and processing of surface water is not a sustainable solution; surface water should be managed at source and not transferred, with every option investigated before discharging surface water into a public sewerage network. The expectation will be for only foul flows to communicate with the public sewer. Applicants wishing to discharge to public sewer will need to submit clear evidence demonstrating why alternative options are not available. A discharge to groundwater or watercourse may require the consent of the Environment Agency or Lead Local Flood Authority.
4.100 However, it is not always appropriate to discharge surface water runoff from certain catchments to the environment prior to sufficient levels of treatment. Proposals for SuDS schemes should always be designed to incorporate sufficient treatment stages to make sure that the final discharge is treated to such a standard as is appropriate for the receiving environment. Further information is available from the Environment Agency in its groundwater protection guidance and position statements and The SuDS Manual (CIRIA). Approved schemes will be expected to be supplemented by appropriate maintenance and management regimes for the lifetime of any surface water drainage schemes.
4.101 Any development proposal that is part of a wider development/allocation should demonstrate how the site delivers foul and surface water drainage as part of a wider strategy, having regard to interconnecting phases of development. It will be necessary to make sure the drainage proposals are part of a wider, holistic strategy that coordinates the approach to drainage between phases, between developers, and over a number of years of construction. The applicant will be expected to include details of how the approach to foul and surface water drainage on a phase of development has regard to interconnecting phases in a larger site. Infrastructure should be sized to accommodate flows from interconnecting phases and drainage strategies should make sure a proliferation of pumping stations is avoided on a phased development. This will make sure that a piecemeal approach to drainage is avoided and that any early phases of development provide the drainage infrastructure to meet the needs of any later interconnecting phases of development. In delivering drainage as part of a wider strategy, applicants will be expected to ensure unfettered rights of discharge between the various parcels of development in a wider development to prevent the formation of ‘ransom situations’ between separate phases of development.
4.102 The Canal & River Trust is not a land drainage authority and surface water discharges from developments into Canal & River Trust waterways are not granted as of right; where they are granted they will be subject to completion of a commercial agreement.
4.103 A critical drainage area is defined in the Town and Country Planning (General Development Procedure) (Amendment) (No.2) (England) Order 2006 as “an area within flood zone 1 which has critical drainage problems and which has been notified…[to]…the local planning authority by the Environment Agency." The Environment Agency has not identified or allocated any critical drainage areas in Cheshire East.
4.104 Development(s) shall be situated to avoid the risk of flooding. Where this cannot be achieved, any developments situated in areas at risk of flooding must be designed to make sure they are made safe for their lifetime and do not increase the risk of flooding onsite or elsewhere, taking into account the impact of climate change. Mitigation of flood risk shall be achieved by incorporating on-site measures. Off-site measures shall only be considered where proposed on-site measures are inadequate or where no alternative can be provided. Examples of proposals that could reduce the risk of flooding include mitigation/defence/alleviation work, retro-fitting of existing development, and off-site detention/retention for catchment-wide interventions.
4.105 The council's Local Flood Risk Management Strategy (2017) notes that culverting:
- can damage the ecology of a watercourse;
- introduces an increased risk of blockage, with a consequent increase in flood risk; and
- can complicate maintenance because access into the culvert is restricted (in some cases being classified as a confined space and requiring trained operatives and specialist equipment).
- Preliminary Flood Risk Assessment (2011, Jacobs)
- Preliminary Flood Risk Assessment Addendum (2017, Cheshire East Council)
- Cheshire East Strategic Flood Risk Assessment (2013, JBA Consulting)
- Cheshire East Local Flood Risk Management Strategy (2017, Cheshire East Council)
- The Water Environment (Water Framework Directive) (England and Wales) Regulations 2003
- Catchment Flood Management Plans (2009, The Environment Agency)
- Non-Statutory Technical Standards for Sustainable Drainage Systems (2015, DEFRA)
- Groundwater protection guidance documents (The Environment Agency and DEFRA)
- Position statements: The Environment Agency's Approach to Groundwater Protection (2018, The Environment Agency)
- The SuDS Manual (2015, CIRIA)
- Surface Water Drainage (PDF, 11.0MB) (2015, The Canal & River Trust)
(Footnote 10) Due to design limitations not all highways drains will be suitable points of discharge and due consideration will need to be given on a site specific basis.
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