ÖйúPÕ¾

1. Introduction to Sustainable Drainage System Design (SuDS) Guidance

1.1 The Town and Country Planning (Development Management Procedure) (England) Order 2015, makes ÖйúPÕ¾ (SCC) as Lead Local Flood Authority (LLFA), the statutory consultee for surface water drainage for all major planning applications in the County.

1.2 The LLFA is required to provide consultation responses on the surface water drainage provisions associated with major development to the Local Planning Authority (LPA).

1.3 This guidance sets out the LLFA’s requirements for surface water management provisions for major development.

1.4 SuDS are mandatory on all planning applications which could affect drainage on or around a development site in England.

1.5 Where a site is significant in size, is hydrologically complex or where a proposed approach goes against the advice contained in this guidance, it is strongly advised that applicants seek pre-application advice from SCC as LLFA, prior to submission of their application (see Section 7).

1.6 This guidance represents advice from the LLFA relating to surface water drainage and sets out the minimum operating requirements as set out in the and . It does not cover in detail other considerations the LLFA may take into account such as works affecting Ordinary Watercourses or specific requirements of Flood Risk Assessments (FRAs). These can be found on either the SCC or Local Planning Authority (LPA) webpages. Meeting the requirements set out in this guidance will assist the LLFA in assessing the application, enabling a more streamlined assessment process.

1.7 For any queries relating to this advice or other SuDS matters please contact us at: SuDS@surreycc.gov.uk.

2. Vision for ÖйúPÕ¾

2.1 SuDS are an approach to managing surface water runoff which seeks to mimic natural drainage systems and retain water on or near the site as opposed to traditional drainage approaches which involve piping water off-site as quickly as possible. SuDS offer significant advantages over conventional piped drainage systems in reducing flood risk by attenuating the rate and quantity of surface water runoff from a site, promoting groundwater recharge and biodiversity benefits, as well as improving water quality and amenity value.

2.2 SCC's Vison as stated in its Local Flood Risk Management Strategy is to make ÖйúPÕ¾ more resilient to flooding on a long-term basis through a coordinated approach with residents and partners. Objective 6 of the strategy, which deals with Planning, states:

"We will reduce the risk of flooding to and from development through local planning policy and processes."

To achieve this we will:

• Undertake a robust statutory consultee role on surface water drainage
• Influence policy and advise Local Planning Authorities on managing flood risk
• Take viable opportunities to utilise existing and new development to reduce flood risk
• Educate planning officers, Members and developers on flood risk and drainage, particularly SuDS and environmentally beneficial measures

3. Requirement for SuDS

3.1 In accordance with the Ministerial Statement HCWS161 and The Town and Country Planning (Development Management Procedure) (England) Order 2015, as the LLFA, SCC the statutory consultee for surface water for all major planning applications.

3.2 It should be noted that SCC as LLFA is not a statutory consultee in respect of groundwater and this falls outside of our role in planning as defined above. However applicants should consider and mitigate for any potential impacts of groundwater on the management of surface water.

3.3 A surface water drainage assessment should be carried out to demonstrate that the proposed development makes use of SuDS and will not increase surface water flood risk to the development site and surrounding area. The submitted Drainage Strategy should be in accordance with the NPPF, the Planning Practice Guide (PPG), the appropriate LPA Local Plan, Neighbourhood Plan, Strategic Flood Risk Assessments (SFRA) and Supplementary Planning Documents (SPD) where appropriate.

3.4 The proposed design of the surface water drainage system must adhere to the .

3.5 NPPF Paragraph 181 (Feb 2025) states:

“When determining any planning applications, local planning authorities should ensure that flood risk is not increased elsewhere. Where appropriate, applications should be supported by a site-specific flood-risk assessment. Development should only be allowed in areas at risk of flooding where, in the light of this assessment (and the sequential and exception tests, as applicable) it can be demonstrated that:

a. within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location;

b. the development is appropriately flood resistant and resilient such that, in the event of a flood, it could be quickly brought back into use without significant refurbishment;

c. it incorporates sustainable drainage systems, unless there is clear evidence that this would be inappropriate;

d. any residual risk can be safely managed; and

e. safe access and escape routes are included where appropriate, as part of an agreed emergency plan.”

3.6 NPPF Paragraph 182 (Feb 2025) states:

“Applications which could affect drainage on or around the site should incorporate sustainable drainage systems to control flow rates and reduce volumes of runoff, and which are proportionate to the nature and scale of the proposal. These should provide multifunctional benefits wherever possible, through facilitating improvements in water quality and biodiversity, as well as benefits for amenity. Sustainable drainage systems provided as part of proposals for major development should:

a. take account of advice from the Lead Local Flood Authority;

b. have appropriate proposed minimum operational standards; and

c. have maintenance arrangements in place to ensure an acceptable standard of operation for the lifetime of the development.”

3.7 Consideration of the provisions under NPPF paragraphs 181 and 182 should be made for all major developments, but the decision on whether a particular form or type of sustainable drainage system would be appropriate for a particular development proposal is a matter of judgement for the LPA, based on advice from the LLFA, who will have considered the type of drainage system to be reasonably practicable for the development.

4. Surface water drainage evidence required

The applicant should clearly set out how they have met each of the within their Drainage Strategy. It is recommended that each standard is addressed in a separate section of a Drainage Strategy (or document).

In accordance with 3.25 of the National standards for sustainable drainage systems, non-technical summaries should also be provided.

4.1 Standard 1: runoff destinations

4.1.1 The Applicant must follow the hierarchy set out in Standard 1.1 of the National standards for sustainable drainage systems

4.1.2 ÖйúPÕ¾ is located within a ‘Water Stressed Area’ as defined in the Environment Agency’s Water stress areas – 2021 classification and therefore Priority 1 will always be required as per 1.11 of the National standards for sustainable drainage systems.

4.1.3 It is acknowledged that Priority 1 (collected for non-potable use) will normally be proposed in conjunction with another lower order priority, in the majority of cases an outfall from the site will be required (e.g. to ground or off-site).

4.1.4 There are areas of ÖйúPÕ¾ 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 must be provided at the planning application stage.

4.1.5 If infiltration test results are not available to support a Planning Application, then full 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. Justifications will be reviewed on a case-by-case basis. A suitable desk study of ground conditions should be submitted.

4.1.6 In ÖйúPÕ¾ there are areas where deep bore soakaways may be an appropriate method of draining the site with appropriate water quality and geotechnical considerations, subject to any necessary approvals from the Environment Agency.

4.1.7 SCC LLFA will not be considering use of 1.6.1 from the National standards for sustainable drainage systems.

4.1.8 For discharge to a watercourse the applicant must demonstrate the onward connectivity, condition and capacity of the watercourse to receive flows.

4.1.9 New private surface water drainage will not be allowed to discharge into a highway drainage system.

4.1.10 If the development site has an existing connection to the highway drainage system, please contact SCC Highways to discuss the proposals.

4.1.11 Surface water from private land must not discharge onto the public highway surface or into the public highway drainage system.

4.1.12 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 6. Other approvals required). The Applicant must refer to the need to obtain any consents, licences or permissions within their Drainage Strategy.

4.2 Standard 2: management of everyday rainfall (interception)

4.2.1 If any surface water is discharged from the site, the applicant must supply a plan which clearly identifies the type and size of SuDS and demonstrates the areas which drain to those features. A table should also be provided which demonstrates the areas draining to each feature and how those areas comply with the standard.

4.3 Standard 3: management of extreme rainfall and flooding

Infiltration:

4.3.1 On sites where infiltration is proposed to drain surface water, the applicant should provide a table for each soakaway which should include the following information: cover level, invert level, soakaway depth, area drained to soakaway, attenuation volume, rainfall design event, climate change allowance, factor of safety (in accordance with Table S3.1 from the National standards for sustainable drainage systems), depth to highest recorded ground water level and infiltration rate used.

Runoff Rates:

4.3.2 Discharge rates should be limited to the lowest achievable 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 be used.

4.3.3 For brownfield sites the expectation is that the relaxation factor will only apply in exceptional circumstances.

4.3.4 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).

Exceedance Events:

4.3.5 An exceedance flow routing plan demonstrating no increase in surface water flood risk on or off site should be submitted. The plan must include proposed levels and flow directions. This information will be considered at the application stage, with the detailed design information (if not supplied) required at the pre-commencement condition stage.

4.4 Standard 4: water quality

4.4.1 The applicant must provide a section within the Drainage Strategy or a standalone document which confirms how this standard has been met.

4.4.2 In relation 4.16.1(b) of the National standards for sustainable drainage systems, ‘the vicinity of the site’ relates to within 100 metres of the infiltration feature with evidence of the same hydrogeological conditions.

4.5 Standard 5: amenity

4.5.1 The applicant must provide a section within the Drainage Strategy or a standalone document which confirms how this standard has been met.

4.5.2 Whilst the wider amenity benefits are outside the LLFA’s remit, it is still a functional part of the principles of SuDS and should therefore be incorporated into drainage designs.

4.5.3 The specific requirements of this standard may be assessed by other consultees.

4.6 Standard 6: biodiversity

4.6.1 The applicant must provide a section within the Drainage Strategy or a standalone document which confirms how this standard has been met.

4.6.2 Whilst the wider ecology and biodiversity is outside the LLFA’s remit, it is still a functional part of the principles of SuDS and should therefore be incorporated into drainage designs.

4.6.3 The specific requirements of this standard may be assessed by other consultees.

4.7 Standard 7: design of drainage for construction, operation, maintenance, decommissioning and structural integrity

Construction / Structural Integrity:

4.7.1 Responsibility for design safety and structural integrity of individual surface water drainage elements is set out in the construction Design and Management Regulations (CDM) Regulations which is not within the LLFA’s remit to assess.

4.7.2 The applicant must provide a section within the Drainage Strategy or a standalone document which confirms how this standard has been met, including design life, construction risks and phased development where applicable. This information will be considered at the application stage, with the detailed information (if not supplied) required at the pre-commencement condition stage.

Maintenance and Management Plan

4.7.3 At the planning application stage future maintenance and access requirements must be considered and clearly set out in the Drainage Strategy to enable agreement of the principles.

4.7.4 The detailed information as listed in the National standards for sustainable drainage systems will be considered at the application stage, with the detailed information (if not supplied) required at the pre-commencement condition stage. Additionally, the applicant should provide a plan which clearly demonstrates maintenance responsibilities.

5 Standard Conditions

5.1 There are a number of areas where it is acceptable, and in some cases preferred, to use conditions to allow detailed information to be provided post full planning approval; our standard conditions are set out below, which will be applied unless this information is provided (in full) at submission stage. The wording of the conditions will be deemed acceptable by the applicant unless the LPA is notified otherwise.

5.2 Standard conditions for new planning application consultations received from 6th October 2025

Condition 1

The development hereby permitted shall not commence until details of the final design of a surface water drainage scheme have been submitted to and approved in writing by the planning authority. The final solution should follow the principles set out in the approved drainage strategy. The design must satisfy the SuDS Hierarchy and be compliant with the National standards for sustainable drainage systems and the NPPF. The required drainage details shall include:

1. The results of infiltration testing completed in accordance with Building Research Establishment (BRE) Digest: 365 and confirmation of groundwater levels. Where infiltration is proposed confirmation is required of a 1m unsaturated zone from the base of any proposed soakaway to the seasonal high groundwater level and confirmation of half-drain times.
2. Evidence that the receiving watercourse has onward connectivity and capacity to receive flows from the site.
3. Evidence that the surface water drainage system meets the management of everyday rainfall (interception) requirements of the National Standards.
4. Hydraulic calculations to demonstrate the proposed final solution will effectively manage the 1 in 30 (+% allowance for climate change) & 1 in 100 (+% allowance for climate change) storm events and 10% allowance for urban creep. If infiltration is deemed unfeasible, associated discharge rates and storage volumes shall be provided using a maximum discharge rate of xx l/s.
5. Detailed design drawings for all sustainable drainage elements including cross sections and detailed drainage layout plan.
6. An exceedance flow routing plan demonstrating no increase in surface water flood risk on or off site. The plan must include proposed levels and flow directions.
7. Evidence that the surface water drainage system meets the water quality requirements of the National Standards.
8. Evidence that the surface water drainage system meets the amenity requirements of the National Standards.
9. Evidence that the surface water drainage system meets the biodiversity requirements of the National Standards.
10. Details of drainage management responsibilities and maintenance regimes for all drainage elements.
11. Details of how surface water will be managed during construction including measures to protect on site and downstream systems prior to the final drainage system being operational. Including details of how existing watercourse on and adjacent to the site will be protected.

Reason: To ensure the design meets the national standards for sustainable drainage systems and the final drainage design does not increase flood risk on or off site.

Condition 2

Prior to the first occupation of the development, a verification report must be submitted to and approved by the Local Planning Authority. This must demonstrate that the surface water drainage system has been constructed as per the agreed scheme (or detail any minor variations), confirming any defects have been rectified. Provide the details of any management company. Provide an ‘As-Built’ drainage layout and state the national grid reference of key drainage elements.

Reason: To ensure the surface water drainage system is constructed to the national standards for sustainable drainage systems.

5.2 Standard conditions for planning application consultations received prior to 6th October 2025

Condition 1

The development hereby permitted shall not commence until details of the final design of a surface water drainage scheme have been submitted to and approved in writing by the planning authority. The final solution should follow the principles set out in the approved drainage strategy. The design must satisfy the SuDS Hierarchy and be compliant with the national standards for sustainable drainage systems and the NPPF. The required drainage details shall include:

1. The results of infiltration testing completed in accordance with BRE Digest: 365 and confirmation of groundwater levels. Where infiltration is proposed confirmation is required of a 1m unsaturated zone from the base of any proposed soakaway to the seasonal high groundwater level and confirmation of half-drain times.
2. Evidence that the receiving watercourse has onward connectivity and capacity to receive flows from the site.
3. Hydraulic calculations to demonstrate the proposed final solution will effectively manage the 1 in 30 (+% allowance for climate change) & 1 in 100 (+% allowance for climate change) storm events and 10% allowance for urban creep. If infiltration is deemed unfeasible, associated discharge rates and storage volumes shall be provided using a maximum discharge rate of xx l/s
4. Detailed design drawings for all sustainable drainage elements including cross sections and detailed drainage layout plan.
5. An exceedance flow routing plan demonstrating no increase in surface water flood risk on or off site. The plan must include proposed levels and flow directions.
6. Details of drainage management responsibilities and maintenance regimes for all drainage elements.
7. Details of how surface water will be managed during construction including measures to protect on site and downstream systems prior to the final drainage system being operational. Including details of how existing watercourse on and adjacent to the site will be protected.

Reason: To ensure the design meets the national standards for SuDS and the final drainage design does not increase flood risk on or off site.

Condition 2

Prior to the first occupation of the development, a verification report must be submitted to and approved by the Local Planning Authority. This must demonstrate that the surface water drainage system has been constructed as per the agreed scheme (or detail any minor variations), confirming any defects have been rectified. Provide the details of any management company. Provide an ‘As-Built’ drainage layout and state the national grid reference of key drainage elements.

Reason: To ensure the Drainage System is constructed to the national standards for SuDS.

6. Other approvals required

6.1 Watercourse regulation

6.1.1 If the site works propose to culvert, divert or create any other obstruction in a watercourse, the granting of planning permission does not represent permission to carry out these works.

6.1.2 Prior to construction, written consent under Section 23 of the Land Drainage Act 1991 is required from SCC for works to an ordinary watercourse.

6.1.3 Consent may be required from the Environment Agency for works to and within 8m of a Main River.

6.1.4 Where these works would affect development viability or site layout, agreement in principle should be sought at pre-planning submission stage to ensure it is likely to be forthcoming.

6.2 Groundwater quality

6.2.1 If proposed works result in 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.

7. Pre-application planning advice

7.1 SCC provide three levels of pre-application advice. The SuDS Planning advice webpage provides further information and associated costs.