1. Introduction to Sustainable Drainage Systems (SuDS) for non-major development
Requirement for SuDS
1.1 As set out in the National Planning Policy Framework (NPPF), SuDS are mandatory on all planning applications affecting drainage on or around a development site in England.
1.2 SuDS are an approach to managing surface water runoff which mimics natural drainage and retains water on or near the surface, supporting biodiversity, improving water quality, and promoting amenity benefits and groundwater re-charge; as opposed to traditional drainage systems which involve piping water off site as quickly as possible.
1.2 This guidance represents advice from the Lead Local Flood Authority (LLFA) relating to surface water drainage and sets out our requirements which should be read in conjunction with the National standards for sustainable drainage.
Surrey County Council's role as LLFA in non-major development
1.3 Surrey County Council as LLFA will provide a bespoke response to consultations by Local Planning Authorities (LPA) on non-major development within the 1% Annual Exceedance Probability (AEP) (1 in 100-year rainfall event) surface water flood risk extent (at any depth), and sites which contain, or are immediately adjacent to, a recorded watercourse. We may also comment on other applications upon a specific request by the LPA.
1.4 Non-major development is classified as:
- 1 to 9 dwellings or areas less than 1 hectare
- Commercial sites where the floor space is less than 1,000 square metres
1.5 Non-major planning applications will be considered by the LLFA as a non-statutory consultee, with comments issued as advice/recommendations for the LPA only. However, the LLFA is regulatory body for changes to ordinary watercourses no matter the scale of the development.
1.6 The LPA may use this guidance alongside the national standards for sustainable drainage to support their review of non-major planning applications that fall outside of the threshold defined above.
1.7 We encourage applicants to seek pre-application advice from Surrey County Council as LLFA, (see Section 4) particularly where a site is hydrologically complex or where a proposed approach goes against our advice in this guidance or the national standards for sustainable drainage.
1.8 For any queries relating to this advice or other SuDS matters please contact: SuDS@surreycc.gov.uk.
2. Surface water drainage evidence required
2.1 For non-major development the applicant should clearly set out within their surface water drainage strategy how they have considered the National standards for sustainable drainage in a proportional way. It is recommended that each standard is addressed in a separate section of a drainage strategy (or other evidence document).
2.2 A statement and a surface water drainage plan should be submitted with the planning application to the LPA, which details how surface water will be managed on site. This should demonstrate that development will not increase surface water flood risk on or off site.
Complying with the National standards for sustainable drainage systems
2.3 Standard 1: Runoff destinations
2.3.1 The applicant must follow the drainage hierarchy set out in standard 1.1 of the National standards for sustainable drainage systems.
2.3.2 Surrey is located within a ‘Water Stressed Area’ as defined in the Environment Agency’s Water stress areas – 2021 classification Policy Paper and therefore collection of water for non-potable use (Priority 1) will always be required in accordance with section 1.11 of the National standards for sustainable drainage systems.
2.3.3 It is acknowledged that Priority 1 disposal will normally be proposed in conjunction with another method of lower order priority, in most cases an outfall from the site will still be required (e.g. to ground or off-site).
2.3.4 Infiltration (Priority 2) test results should accompany planning applications.
2.3.5 If infiltration test results are not available to support a planning application, then justification as to why these have not been provided should be included. For example, issues with site access i.e. the site is a working brownfield site and as such it is not possible to dig trial pits. A suitable desk study of ground conditions should be submitted. If infiltration is proposed without test results, other suitable evidence to show the viability of the design should be included.
2.3.6 Surrey County Council as LLFA will not be using its powers as set out in section 1.6.1 of the National standards for sustainable drainage systems for delivering third party developments.
2.3.7 For discharge to a watercourse (Priority 3), the applicant must demonstrate the onward capacity, connectivity and condition of the watercourse to receive flows.
2.3.8 New private surface water drainage will not be allowed to discharge into a SCC highway drainage system, and surface water from private land must not discharge onto the public highway surface.
2.3.9 If the development site has an existing connection to the highway drainage system, please contact us to discuss the proposals, as continued use is not guaranteed.
2.3.10 The granting of planning permission and agreement of the principles of how surface water will be disposed of, from a site does not absolve the requirement to gain Ordinary Watercourse Consent or an Environmental Permit when connecting to a watercourse (see Section 3). The applicant must refer to the need to obtain any consents, licences or permissions within their drainage strategy, and their current status.
2.3.11 There are areas of Surrey that are only served by foul sewers, in these circumstances where a higher priority outfall has been demonstrated as unfeasible (with supporting evidence submitted), there may be a requirement for a connection to the foul sewer subject to the approval of the sewerage authority. Evidence of this approval must be provided at the planning application stage to ensure viability of the proposals.
2.4 Standard 2: Management of everyday rainfall (interception)
2.4.1 If the proposal is not using infiltration, the first 5mm of any rainfall event must be managed on site. The applicant must supply a plan which clearly identifies the type and size of SuDS features used to achieve this and show the areas which drain to those features.
2.4.2 If surface water is managed through SuDS features or systems such as a swale, SuDS planter, raingarden, attenuating tree pits or permeable paving etc, the requirements of this standard would be met.
2.5 Standard 3: Management of extreme rainfall and flooding
Infiltration
2.5.1 On sites where infiltration is proposed to drain surface water, the applicant should confirm the site infiltration rate and that there is 1m separation between the base level of the feature and the depth to the highest recorded ground water level.
Runoff rates
2.5.2 Surface water discharge rates should be limited to as close as possible to the greenfield rate for the designed storm event. Where a sewerage undertaker states a maximum discharge rate in their developer enquiry response, the lowest achievable rate should still be used.
2.5.3 For brownfield sites the expectation is that the relaxation factor will only apply in exceptional circumstances. See section 3.21 and 3.21.1 in the National standards for sustainable drainage systems.
2.5.4 For most sites where development is increasing the volume of runoff the allowable discharge rate will be limited to the 50% Annual Exceedance Probability (AEP) (1 in 2 year return period).
Exceedance events
2.5.5 An exceedance flow route plan demonstrating no increase in surface water flood risk on or off site should be submitted. The plan must include existing and proposed levels and flow directions.
2.6 Standard 4: Water quality
2.6.1 If surface water is managed through above ground SuDS features or systems such as a swale, SuDS planter, raingarden, attenuating tree pits or permeable paving etc, the requirements of this standard would be met. If the site has a use which presents a specific risk to water quality, measures to mitigate the risk or remediation maybe required.
2.7 Standard 5: Amenity
2.7.1 If surface water is managed through SuDS features or systems such as a swale, SuDS planter, raingarden, attenuating tree pits or permeable paving and so on, the requirements of this standard would be met.
2.8 Standard 6: Biodiversity
2.8.1 If surface water is managed through vegetated SuDS features or systems such as a green roof, planted swale, SuDS planter, raingarden, attenuating tree pits etc., the requirements of this standard would be met.
2.9 Standard 7: Design of drainage for construction, operation, maintenance, decommissioning and structural integrity
Construction / Structural integrity
2.9.1 Responsibilities for design safety and structural integrity of individual surface water drainage elements are set out in the Construction Design and Management (CDM) Regulations which is not within the LLFA’s remit to assess.
Maintenance and management Plan
2.9.2 At the planning application stage, future maintenance and access requirements must be considered and clearly set out in the drainage strategy.
3. Legislation, Policy and Other Approvals Required
Local Planning Authority (LPA) policy and guidance
3.1 The submitted drainage strategy should be in accordance with the appropriate LPA Local Plan, Neighbourhood Plan, Strategic Flood Risk Assessments (SFRA) and Supplementary Planning Documents (SPD) where appropriate.
Watercourse regulation
3.2 Development proposals should not enclose, or restrict maintenance access to existing watercourses and should, where possible, remove existing culverts and re-naturalise existing river channels; unless to do so would increase flood risk or result in other environmental harm.
3.3 If there is a proposal to culvert, divert or create any other obstruction in a watercourse, additional consents as detailed below are required. Please note the granting of planning permission does not guarantee permission to carry out these works.
3.4 For works to an ordinary watercourse, written consent under Section 23 of the Land Drainage Act 1991 is required from Surrey County Council prior to construction. See Ordinary watercourse consenting for details.
3.5 For works to and within 8m of a Main River consent may be required from the Environment Agency. See Flood risk activities: environmental permits for details.
3.6 Where works to a watercourse would affect development viability (such as access or layout), agreement in principle should be sought at pre-planning submission stage.
Groundwater quality
3.7 If proposed works include infiltration of surface water to ground within a Source Protection Zone, the Environment Agency will require proof of sufficient surface water treatment to achieve water quality standards to prevent groundwater pollution.
4. Pre-application planning advice
4.1 Surrey County Council provide three levels of pre-application advice. For further information and associated costs, see Pre-application planning advice.