Flood risk and drainage guidance for developers
East Sussex County Council (as the Lead Local Flood Authority or LLFA) provides a strategic flood risk role across East Sussex. As part of this role, we are a statutory planning consultee in relation to flood risk and rainwater/ surface water drainage for major planning applications across the county.
Our advice to the Local Planning Authorities (LPAs) is considered alongside other consultation responses and planning matters during the determination process. Planning decisions are the sole responsibility of the relevant LPA and the LLFA does not have the power to alter a planning decision.
National Standards for Sustainable Drainage
On 19th June 2025 DEFRA published the new ‘National Standards for Sustainable Drainage (SuDS)’. These standards are intended to be used in the design of surface water drainage systems for all new infrastructure and development, whether on greenfield or brownfield sites.
These standards replace the ‘Non-Statutory Guidance for SuDS’ and immediately became a material planning consideration.
The National Standards for Sustainable Drainage (SuDS) promotes consistency of approach and helps ensure long-term performance and resilience. It incorporates seven (7) standards against which a drainage design will be considered.
East Sussex LLFA requires evidence that all new applications have taken into consideration the National Standards for Sustainable Drainage. It is recommended that a summary page is included within any drainage strategy which outlines how each standard has been addressed within the development of the design.
East Sussex flood risk and drainage policies and guidance
Deep-bored soakaways
In line with advice received from the Environment Agency, ESCC generally oppose the use of deep-bored soakaways as a means of managing surface water drainage on developments. The reasoning for this opposition is two-fold.
- The increased risk of groundwater contamination due to direct discharge of waters into groundwater.
- The potential impact on local groundwater levels and flows which can increase the likelihood of groundwater reaching the surface (and potentially increasing flood risk).
ESCC recommend that deep-bored soakaways are used as a last resort where the ground conditions are suitable, and the groundwater levels are known. The County Council requires that the following criteria are met when deep bored soakaways are proposed:
- Investigations showing there are no other alternative surface water destinations.
- The depth of the system should be no deeper than what is required for soakage.
- A minimum of two water treatment stages using SuDS measures must be provided upstream of the soakaway.
- An unsaturated zone must be provided below the base of the structure. There should be a minimum of 10m between the base of the structure and recorded maximum winter groundwater level.
Development near watercourses and culverts
The Lead Local Flood Authority requires a minimum 5m no development buffer from the top of bank, or edge of culvert for all ordinary watercourses. This buffer is required to maintain access to the watercourse for ongoing maintenance and management of the watercourse.
Should a 5m buffer be considered unrealistic by a developer we advise that this is raised as part of pre-application conversations.
Where other policies or guidance require a no development buffer from a watercourse, we advise that the maximum buffer distance should be utilised.
Groundwater monitoring
In line with best practice and national guidance, ESCC require groundwater monitoring results to be provided as part of drainage design submissions.
The County Council can provide the following guidance on our requirements for groundwater monitoring:
- Groundwater monitoring should be undertaken over a 6-month winter period
- Our preferred monitoring period is October - March, although November - April is also considered acceptable.
- Groundwater monitoring locations should consider potential drainage locations and any below ground development such as basements.
We would also advise that any designs based on the groundwater monitoring should also utilise published or publicly available groundwater data, including the BGS depth to groundwater dataset. This is to help ensure that wider impacts on groundwater conditions, such as extended dry periods, are considered within designs.
Comments from third parties on flood risk matters relating to planning applications
We are aware that development proposals, particularly those of a significant size, can often give rise to flood risk and drainage related concerns from members of the public and community groups and organisations. Should you have such concerns then you will need to put these to the relevant Planning Authority during the consultation stage of the planning application. It may be the case that the County Council, as the LLFA, provides comments on such applications that differ from your own views. In this regard, it is important to note that the County Council has to consider and appraise the development proposal in an objective manner, having regard to robust evidence and relevant planning policies, which includes the Government’s National Planning Policy Framework.
With the above in mind, should an individual or organisation wish to challenge the advice we have provided on a planning application then they will need to do so through the relevant Planning Authority. It will then be for the planning authority to decide whether they wish to seek further clarity or advice or reconsideration of position from the County Council. Ultimately it needs to be the planning authority who are content with the advice we are providing as they will be making the decision on the application in question.
It is recognised that very occasionally, a third party (i.e. member of public, town or parish council, etc.) may identify a factual error in either the flood risk evidence that supports the application and or our response to the application. Should this be the case then please contact the County Council highlighting what this factual error is. In turn, we will review our representation, amend it where necessary and maintain a close dialogue with the relevant planning authority and applicant, if necessary. We will respond to the individual or organisation that have highlighted the error to explain what course of action we have taken.
Any correspondence we receive that expresses concerns over flood risk matters, within the context of a planning application, will be sent to the relevant planning authority for their consideration in the determination of the application. In such cases we will acknowledge the correspondence and explain who we have passed it onto and how it will be considered. If you have concerns over sharing of the correspondence between the Local Authorities, please take a look at our privacy notice.
Support for developers
East Sussex Flood Risk Management team can provide support and advise to developers at all stages of development and planning. We highly recommend discussing the flood risk and drainage potential of a site as part of the masterplan stage as this ensures both are considered early. Early consideration of drainage helps meet the requirements of the new National Standards for Sustainable Drainage.
Details of the services we provide can be found on “Support and Services we Provide".