Design and construct SuDS for new developments

When you need SuDS and which rules apply

If you are developing land in England or Wales, you will almost certainly need to incorporate sustainable drainage systems (SuDS) into your surface water drainage strategy. SuDS manage rainwater close to where it falls, reducing flood risk, improving water quality, and creating amenity and biodiversity value.

The regulatory requirements differ significantly between England and Wales, even though both stem from the Flood and Water Management Act 2010:

• England -- Schedule 3 has not been commenced. SuDS requirements are delivered through the planning system. The NPPF expects major developments to incorporate SuDS, and the Lead Local Flood Authority (LLFA) is a statutory consultee. If the LLFA objects and the objection is unresolved, the planning authority is expected to refuse permission
• Wales -- Schedule 3 was commenced on 7 January 2019, creating a mandatory SuDS Approval Body (SAB) process. You cannot start construction on any development with a construction area of 100 square metres or more, or more than 1 dwelling, without SAB approval. Building without approval exposes you to SAB stop and enforcement notices, and failing to comply with a notice is a criminal offence carrying an unlimited fine

Getting the approach wrong for your jurisdiction can cause serious delay, enforcement action, or criminal liability. If you work across both nations, follow the correct route for each site.

Design your SuDS to CIRIA C753 standards

The CIRIA SuDS Manual (C753) is the accepted industry standard for SuDS design in both England and Wales. Whether your scheme must satisfy an LLFA or a SAB, C753 is the reference point that approving bodies assess against.

The SuDS management train

Design drainage using the management train hierarchy, managing surface water as close to source as possible:

1. Prevention -- minimise impermeable surfaces and protect natural drainage features
2. Source control -- manage rainfall where it falls (permeable paving, green roofs, rain gardens, soakaways)
3. Site control -- collect water from source controls using swales, detention basins, and filter strips
4. Regional control -- manage larger catchments using retention ponds, wetlands, and flood storage

Use multiple stages rather than relying on a single attenuation feature. This provides better water quality treatment and greater resilience.

The four pillars

C753 requires SuDS to deliver across four areas: water quantity (match greenfield runoff), water quality (treat pollutants), amenity (enhance the development), and biodiversity (support habitats). Designs addressing only water quantity are unlikely to satisfy review. In Wales, all four pillars are an explicit statutory requirement.

Choosing SuDS components

Select components based on site constraints, soil conditions, and treatment needs:

• Permeable paving -- water infiltrates through the surface into a sub-base reservoir; suitable for car parks and driveways; requires maintenance to prevent clogging
• Swales -- shallow vegetated channels that convey and treat runoff; effective along road edges and boundaries
• Rain gardens and bioretention -- planted areas with engineered soil media that filter pollutants; attractive in residential settings
• Detention basins -- vegetated depressions for temporary storm storage; normally dry and usable as amenity space
• Retention ponds and wetlands -- permanently wet features providing storage, sedimentation, and biological treatment; high biodiversity value
• Green roofs -- vegetated roof systems absorbing and slowing rainwater; also provide insulation
• Below-ground attenuation -- geocellular crates or tanks; a last resort as they provide no quality, amenity, or biodiversity benefit

Where infiltration is possible (confirmed by BRE 365 percolation testing), prioritise infiltration-based components. Where ground conditions prevent infiltration, use lined systems with controlled discharge.

Obtain the required approvals

The approval process depends on whether your site is in England or Wales.

England: LLFA consultation through planning

Plan adoption and long-term maintenance

Failing to secure clear adoption arrangements before construction is one of the most common SuDS problems. Agree who will adopt and maintain the system before you build, not after.

Adoption routes

• Water company (Section 104 agreement) -- SuDS connected to the sewer network may be adopted under a Section 104 agreement. Design must comply with the Design and Construction Guidance (DCG). Water companies have historically been reluctant to adopt above-ground features such as swales and ponds, though this is improving
• Highway authority (Section 38 agreement) -- SuDS within the highway boundary (roadside swales, permeable paving in adopted roads) may be adopted under a Section 38 Highways Act agreement
• Private management company -- SuDS not adopted by a statutory body are maintained by a management company funded by service charges. This creates long-term risks if the company fails

In Wales, the SAB adopts approved SuDS upon satisfactory completion, providing a statutory adoption route that removes the uncertainty over long-term responsibility.

Construction quality

• Protect SuDS areas -- fence off areas designated for infiltration to prevent soil compaction from construction traffic
• Manage silt -- install temporary silt fences and settlement lagoons; silt from construction will clog permeable surfaces and outlet controls. A water discharge environmental permit may be required
• Phase construction -- build SuDS features after bulk earthworks are substantially complete, or provide temporary drainage
• Use specified materials -- substituting cheaper aggregates or filter media can cause premature failure; for Section 104 adoption, materials must comply with DCG requirements
• Notify for inspections -- the adopting body will inspect at key stages. Notify them before covering drainage infrastructure

Every SuDS scheme needs a maintenance plan specifying what maintenance is required, how often, and who is responsible. Secure this through planning conditions, Section 106 agreements, or SAB approval in Wales.

What to do next

• Site assessment -- commission ground investigation including BRE 365 percolation testing; check Environment Agency flood maps; consult the LLFA or SAB early
• Design -- engage a drainage engineer experienced in CIRIA C753; in Wales, contact the SAB for pre-application advice; in England, check the LLFA's local requirements
• Pre-application -- discuss adoption with the water company (Section 104) and highway authority (Section 38) before finalising design; in Wales, prepare the SAB application
• Construction -- discharge drainage conditions before starting work; protect SuDS areas from traffic and silt; notify the adopting body before covering infrastructure

For broader flood risk requirements including Flood Risk Assessments and Sequential Tests, see Flood risk assessment and SuDS compliance.

For sewer adoption details including bond requirements and the vesting process, see Adopt new sewers under Section 104.