Drainage Strategies & SuDS Design in Sussex

We prepare drainage strategies, SuDS designs and flood risk assessments for planning applications across East Sussex, West Sussex and Brighton & Hove, and help discharge drainage conditions once permission is granted. We work for developers, self-builders, architects and homeowners, from single new homes to small developments.

Get a quote or call 020 3835 2633

What the Sussex flood authorities expect
Sussex has three Lead Local Flood Authorities: East Sussex County Council, West Sussex County Council and Brighton & Hove City Council. They advise the planning authority on surface water drainage for major applications, while district and borough councils usually deal with drainage on smaller schemes, often through planning conditions.
• East Sussex expects a summary showing how each of the seven national SuDS standards has been addressed, and groundwater monitoring over a six-month winter period, preferably October to March. Deep-bored soakaways are only accepted as a last resort, and a 5m buffer is expected from ordinary watercourses.
• West Sussex expects major applications to comply with the national standards, and does not accept lack of space or high-density housing as a reason to leave out source control SuDS. Infiltration in a groundwater Source Protection Zone needs details of how pollution will be prevented.
• Works affecting an ordinary watercourse need the flood authority’s consent before construction.

National standards
Defra’s National Standards for Sustainable Drainage, published in June 2025, now apply to new development, and drainage strategies are expected to show how each standard has been met. The revised NPPF also expects SuDS on development that could affect drainage. Read our NPPF article →

Ground conditions
Sussex ground varies a lot. The chalk of the South Downs can often take infiltration, but groundwater levels and Source Protection Zones need checking. The Weald clays usually drain poorly, so attenuation and controlled discharge are common, and coastal and river floodplain sites can have high groundwater. That’s why winter groundwater monitoring is often the first thing to plan.

Local area pages
We also cover Brighton & Hove, Hastings, Eastbourne & Bexhill and Lewes.

What we provide
• Drainage strategies and SuDS design for planning applications, from single new homes to small developments
• Infiltration testing to BRE 365 and soakaway design
• Flood risk assessments where the site needs one
• Discharging pre-commencement drainage conditions, and responses to the council and the Lead Local Flood Authority
• Water company applications: sewer connections (Section 106), adoption (Section 104), diversions (Section 185) and build-over agreements
• Structural design for the same project, so the drainage and foundations work together

Our drainage work in Sussex
• Combermere Road, Hastings: below-ground drainage specification for a new-build house, and help discharging the planning conditions.
• Rotherfield Close, Brighton: new below-ground drainage for an infill new-build house, and a Section 106 sewer connection application to Southern Water.
• Meads Court, Bexhill-on-Sea: structural and below-ground drainage design for a mixed-use building.
• Downey Close, Hastings: structural and civil engineering for a new townhouse development.
• Wilderness Lane, Hadlow Down: structural and civil engineering for side and rear extensions.
See our projects →

Common questions

Do I need a drainage strategy for one new house in Sussex?
Usually, yes. Even where the flood authority doesn’t comment, the district council will normally ask for a drainage strategy, or attach a drainage condition to the permission.

Why do I need winter groundwater monitoring?
In East Sussex, the flood authority expects groundwater levels measured over the winter, when they are highest, before infiltration can be relied on. Starting early avoids delays to your planning programme.

Who handles sewer connections in Sussex?
Southern Water is the sewerage company across Sussex. We prepare and submit the Section 106 connection, adoption and build-over applications for you.

12+ years’ experience · £1,000,000 PI insurance

SuDS and drainage design →
Civil engineering services →
New build structural and civil engineering →
Flood risk assessments →
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Get in touch or call 020 3835 2633