Drainage Strategies & SuDS Design in Surrey

We prepare drainage strategies, SuDS designs and flood risk assessments for planning applications across Surrey, 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 Surrey County Council expects
Surrey County Council is the Lead Local Flood Authority. As well as major applications, it gives advice on non-major development (1 to 9 homes or sites under 1 hectare) that falls within the 1 in 100 year surface water flood extent or is next to a recorded watercourse. Its guidance asks for:
• A drainage strategy with a section addressing each national SuDS standard, and a surface water drainage plan
• Infiltration test results, or a justified desk study where testing isn’t possible
• An exceedance flow route plan, maintenance and access arrangements, and evidence of the consents needed
• Discharge limited as close as possible to the greenfield rate
• At least 1m between the base of any infiltration feature and the highest recorded groundwater level
• Because Surrey is a water stressed area, rainwater collection for non-potable use is always expected
• No new private surface water discharge to county highway drains or onto the highway
Works to an ordinary watercourse need the county council’s consent under Section 23 of the Land Drainage Act 1991, and works within 8m of a main river may need Environment Agency approval.

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
Much of northern and eastern Surrey sits on London Clay or Weald Clay, which drain poorly, so attenuation with a controlled discharge is often needed. The chalk of the North Downs and the sandier soils in the west can be better for infiltration, but only testing will confirm it.

Local area pages
We also cover Esher & Thames Ditton and nearby Kingston & Surbiton.

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

Common questions

Does the county council comment on small schemes?
Sometimes. For 1 to 9 homes, Surrey County Council comments where the site is in the 1 in 100 year surface water flood extent or next to a recorded watercourse, or when the planning authority asks. Either way, the borough council will expect drainage to be dealt with.

Why is rainwater harvesting required?
Surrey is classed as a water stressed area, so the county council expects rainwater to be collected for non-potable uses such as toilet flushing or garden watering before other drainage options.

Who handles sewer connections in Surrey?
Depending on location, Thames Water or Southern Water. We prepare and submit the 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 →
Other areas: London · Sussex · Kent
Get in touch or call 020 3835 2633