What is a Surface Water Drainage Strategy?
A surface water drainage strategy is a comprehensive plan designed to manage runoff and control the flow of water from a development site. It ensures that drainage is handled sustainably and in compliance with national and local regulations, such as the National Planning Policy Framework (NPPF), the Environment Agency’s guidance, and policies from Local Planning Authorities, including the London Plan.
The strategy begins with an assessment of the site’s existing conditions — including topography, ground permeability, and proximity to watercourses or public sewers. On greenfield (previously undeveloped) sites, the aim is to maintain the site’s natural hydrology as much as possible. On brownfield (previously developed) sites, the strategy typically looks to improve or reuse existing drainage infrastructure, such as soakaways, sewer connections, or outfalls to watercourses.
A robust drainage strategy incorporates the four pillars of Sustainable Drainage Systems (SuDS): water quantity, water quality, amenity, and biodiversity. These principles ensure that surface water is managed in a way that reduces flood risk, improves water quality, creates attractive public spaces, and supports local ecosystems.
Core components of the strategy include identifying flood risks, analysing existing drainage capacity, recommending best management practices, and aligning with relevant planning requirements. An effective implementation schedule, along with a monitoring and maintenance plan, ensures long-term functionality and resilience to climate-related pressures.
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When is a Surface Water Drainage Strategy required?
Albeit there are no national statutory to answer this question, most Local Planning Authorities make validation checklists available to guide developers on this matter.
Most Local Planning Authorities (LPAs) require a drainage strategy to be submitted alongside planning applications for major developments, and increasingly for minor developments in areas sensitive to flooding. This includes both greenfield and brownfield sites.
If the site is located in Flood Zones 2 or 3, or within a Critical Drainage Area, a drainage strategy is usually mandatory to demonstrate how surface water will be managed to avoid increasing flood risk.
What are Sustainable Drainage Systems (SuDS)?
Sustainable Drainage Systems (SuDS) are environmentally friendly ways of managing rainwater runoff. Instead of quickly piping water away, SuDS slow it down, store it, and allow it to soak into the ground or be released gradually. This helps reduce flood risk, improves water quality, and supports wildlife.
- Permeable Paving;
- Green Roofs
- Swales & Rain Gardens
- Soakaways
- Underground geo-cellular tanks
- Detention & Infiltration Basins
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What do Surface Water Drainage Strategies contain?
The level of detail of our deliverables depends on the planning stage and scale of development. Outline planning applications do typically require a conceptual drainage strategy, whereas the discharge of conditions and reserved matters require construction details and liaison with third parties.
- Assessment of sustainable drainage options, with attention to limitations and constraints
- Establishment of hydrology conditions, including greenfield runoff rates and volumes
- Draft of drainage layout plan, showing the location of SuDS and drainage networks
- For detailed drainage strategies, provision of pipework details, storage volumes and discharge rates
- Liaison with third parties, including capacity checks with Sewerage Undertakers
- Construction details to inform construction activities
Can I be asked for a Foul Water Drainage Strategy?
Yes. Under certain circumstances, Local Planning Authorities may impose conditions if the disposal of foul water is not obvious. This is often the case for non-mains solutions, where the use of Small Treatment Plants and drainage fields is required. Our work varies from the liaison with third parties (Environment Agency, Sewerage Undertakers) to the design of off-mains solutions to the best guidance set out in the Building Regulations (2010) and in the British Standards.
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FAQs
What are the National Standards for SuDS (2025)?
Albeit non-statutory, the National Standards for SuDS are strongly recommended and requirement by Local Authorities. These set out benchmarks for design, construction, operation, and maintenance. Local authorities and developers are expected to integrate them into planning and design decisions, aligning with the National Planning Policy Framework.
The Standards set out key principles in terms of water quantity, quality, amenity and biodiversity. The Standards promote the reuse and interception of rainwater.
What type of SuDS should I use?
Infiltration and open SuDS are often at the top of the hierarchy, as these are most suitable to deliver amenity, recreational and bio-diversity benefits.
The latest National Standards for SuDS 2025 set out that interception needs to be provided for the first 5mm of rainfall. Attenuation and infiltration basins, green roofs, permeable paving, swales and rain gardens are some of the preferred SuDS for meeting this criteria.
What is Rainwater Harvesting and how can this help me?
From March 2025, the new National Standards for SuDS set out that rainwater should be reused, as a first priority. This means that the implementation of rainwater harvesting tanks is almost certainly required in water stressed areas or in sites where there is a need of water for non-potable uses, including irrigation.
Do I need to undertake surveys?
Albeit we can work to any assumption in the absence of surveys, these elements of work are highly recommended to minimise the risk for abortive costs during construction.
If the proposals are likely to make use of existing drainage arrangements, a drainage survey is of essence to understand if a gravity connection is possible. Alternatively, if soakaways form part of the design, the Local Planning Authority will most likely require evidence of infiltration rates and groundwater levels.
If some of the information above is not provided, Local Authorities may still grant Planning Permission, subject to the discharge of conditions.
