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Guidance

Surface Water Drainage Statement

Sustainable Drainage Systems (SuDS) are a material consideration as part of planning permission for any major development. This means all major applications should be accompanied by a site-specific drainage strategy or statement that demonstrates that the drainage scheme proposed is in compliance with the National Planning Policy Framework (NPPF) and the Non-Statutory Technical Standards.

Surface Water Drainage Statements help us to ensure that suitable arrangements for adoption and maintenance of the SuDS are in place.

We will not generally adopt or maintain SuDS. Instead we expect as part of any planning application that includes SuDS, an applicant will provide information to demonstrate that suitable adoption and maintenance arrangements are in place.

As an alternative to the Council, the following options are available for applicants to secure the adoption and maintenance of SuDS:

  • A management company to adopt and maintain the SuDS within the development – assurances need to be made that this is a suitable option and definitive evidence should be provided on the suitability and experience of the management company.
  • Other organisation (such as a Parish Council) – assurances need to be made that this is a suitable option and evidence should be provided to the local planning authority by the applicant

Decisions about the suitability of sustainable drainage provision are made by Horsham District Council as we are the Local Planning Authority. However, West Sussex County Council, in its role as Lead Local Flood Authority (LLFA), is a statutory consultee for all major applications.

This page provides advice on completing the statement correctly and further resources that could be useful.

Requirements

Surface Water Drainage Form

In order to provide the required information on surface water drainage from the proposed development, the Surface Water Drainage Statement pro-forma must be completed in full and submitted with any planning application which seeks permission for major development. It must be signed by a competent drainage engineer (recognised by the Engineering Council, the Institution of Civil Engineers or equivalent).

This information contained in this form will be used by West Sussex County Council in its role as Lead Local Flood Authority and ‘statutory consultee’ on SuDs for all ‘major’ planning applications.

The pro-forma is supported by the Defra/EA Guidance on Rainfall Runoff Management and can be completed using freely available tools including SuDS Tools. The pro-forma should be considered alongside other supporting SuDS Guidance, but focuses on ensuring flood risk is not made worse elsewhere. The SuDS solution must operate effectively for as long as the development exists. This pro-forma is based upon current industry standard practice.

Please read the guidance below on completing the form, and download the form.

Form guidance

  • Developers and their design teams need to take into account different factors including the layout of the site, topography and geology when planning and positioning the different SuDS elements for the whole scheme.
  • Depending on whether the planning application is ’Outline’ or ‘Full’ will dictate the level of information required for your Surface Water Drainage strategy statement.
  • Reference should be made to the Association of SuDS Authorities (ASA) Non- Statutory Technical Standards for Sustainable Drainage – Practice Guidance Section 2.14 for the level of information that would facilitate both West Sussex County Council (LLFA) & Horsham District Council in determining whether the application complies with the current National Planning Policy Framework (NPPF) & Planning Policy Guidance (PPG) requirements.
  • SuDS must be properly designed to ensure that the maintenance and operation costs are proportionate and sustainable for the lifetime of the development.
  • Surface water run-off should be controlled as near to its source as possible through a sustainable drainage approach to surface water management. SuDS seek to mimic natural drainage systems and retain water on or near to the site, when rain falls, in contrast to traditional drainage approaches, which tend to pipe water off-site as quickly as possible. SuDS therefore offer significant advantages over conventional piped drainage systems.
  • In accordance with Planning Practice Guidance Paragraph 080, applicants must follow the hierarchy for discharge destinations. Where it is not possible to achieve the first hierarchy, discharge through the grounds (also supported by Approved Document Part H of the Building Regulations 2010), applicants must demonstrate in sequence why the subsequent discharge destination was selected.
  • Where the intention is to dispose to soakaway, these should be shown to work through an appropriate assessment carried out under Building Research Establishment (BRE) Digest 365. All designs shall be based on actual infiltration figures obtained through percolation tests, carried out in accordance to BRE Digest 365. Where such tests cannot be undertaken prior to the start of construction, desktop study will be accepted, based on anticipated geology of the site and/or data from the British Geological Survey. Those will then have to be confirmed through site test at construction phase. House or rubble soakaways are not acceptable.
  • In accordance with CIRIA Report 156, Infiltration Drainage and SuDS Manual (C753), an adequate factor of safety must be applied to the observed infiltration value. The minimum factor of safety acceptable is 2 and that must be increased to reflect the consequences of failure of the system, the topography of the site and the likelihood of flooding.
  • Infiltration units must stand the test of half-emptying the provided storage within 24 hours for up to the 1 in 10 year return period storm (and that is for all rainfall duration events).
  • Subject to the evidence being provided to support the choice of discharge destination, proposals to dispose of surface water into a surface water sewer, highway drain or another drainage system, should be accompanied by evidence of the system having spare capacity downstream.
  • Where an application is part of a larger site which already has planning permission, it is essential that the new proposal does not compromise the drainage scheme already approved.
  • On large application sites, full details of individual development plot discharge and storage constraints, as well as full details of responsibility for controlling the overall surface water management of the site prior to final phase completion, must be also supplied.
  • Where development involves a culvert or any works that may lead to obstruction of flow on a Watercourse, additional consent may be required under the Land Drainage Act 1991. In the case of an Ordinary Watercourse the responsibility for determining Consenting lies currently with Horsham District Council following a local designation agreement. An Ordinary Watercourse is defined as any watercourse not identified as a Main River on maps held by the Environment Agency and DEFRA. Find more information about ordinary watercourse land drainage consent on the West Sussex County Council website.

Download the Surface Water Drainage Statement Form

Additional evidence

In addition to the Surface Water Drainage Statement Form,we require before approving a SuDS scheme and finally discharging any relevant drainage condition imposed on the application, the following from the developer:

  • A verification report from the developer that the SuDS system has been constructed in accordance with the approved design drawings and in accordance with best practice. If the SuDS system could pose a Health and Safety risk, the verification should also include a Health and Safety audit to check that the local community, visitors and operation and maintenance operatives will not be put at risk. For further details see; SuDS Manual (C753 Part E Chapter 36; Health & Safety). The construction verification and audit could be undertaken by an independent body.
  • Evidence that the SuDS have been signed off by an appropriate, qualified, indemnified engineer and are explained to prospect owners via Homeowners Pack plus information that SuDS are entered into the land deeds of the property.
  • An agreement that maintenance is in place over the lifetime of the development; and/or evidence that the SuDS will be adopted by third party.
  • For all site and regional control SuDS, the developer should submit ‘As-built’ drawings and specification sheets for materials used in the construction, plus a copy of Final Completion Certificate.
  • These documents should also be offered to the Lead Local Flood Authority (West Sussex County Council) if the SuDS features are to be designated under Section 21 of the Flood & Water Management Act. This will ensure that all SuDS systems are constructed and maintained to required standard and any changes are registered and agreed with the Local Lead Flood Authority, which takes responsibility for overall local flood risk across West Sussex.

West Sussex policy documents

Applicants are strongly advised to discuss their proposals with West Sussex County Council at the pre-application stage to ensure that an acceptable SuDS scheme is submitted. Email FRM@westsussex.gov.uk

Reference should be made to the Association of SuDs Authorities for guidance on the information required to ensure you comply with the current National Planning Policy Framework (NPPF) and Planning Policy Guidance (PPG) requirements.

To assist developers and their design teams on how to properly plan for SuDS, West Sussex County Council working in partnership with the South East Seven, have prepared the guidance document Water People Places.

West Sussex Policy documents