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:

In England, Schedule 3 has not been commenced, so SuDS requirements come 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.

In 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.

Manage surface water as close to where it falls as you can, using several stages (a "management train") rather than a single attenuation feature: this gives better water quality treatment and more resilience. C753 expects SuDS to deliver on water quantity, water quality, amenity and biodiversity, so designs that address only water quantity are unlikely to satisfy review. In Wales, all four are an explicit statutory requirement.

Choosing SuDS components

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

• Permeable paving lets water soak through the surface into a sub-base reservoir. It suits car parks and driveways but needs maintenance to stop it clogging.
• Swales are shallow vegetated channels that carry and treat runoff, and work well along road edges and boundaries.
• Rain gardens and bioretention areas are planted areas with engineered soil that filter pollutants, and suit residential settings.
• Detention basins are vegetated hollows that store storm water for a short time. They are normally dry and can be used as amenity space.
• Retention ponds and wetlands are permanently wet features that provide storage, sedimentation and biological treatment, with high biodiversity value.
• Green roofs absorb and slow rainwater and also provide insulation.
• Below-ground attenuation, such as geocellular crates or tanks, is a last resort because it gives 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.

LLFA consultation through planning in England

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

• A water company may adopt SuDS connected to the sewer network under a Section 104 agreement, if the design complies with the Design and Construction Guidance (DCG). Water companies have historically been reluctant to adopt above-ground features such as swales and ponds.
• The highway authority may adopt SuDS within the highway boundary, such as roadside swales and permeable paving in adopted roads, under a Section 38 Highways Act agreement.
• SuDS that no statutory body adopts are maintained by a private management company funded by service charges, which 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

• Fence off areas designated for infiltration so construction traffic does not compact the soil.
• Install temporary silt fences and settlement lagoons, because construction silt will clog permeable surfaces and outlet controls. A water discharge environmental permit may be required.
• Build SuDS features after bulk earthworks are substantially complete, or provide temporary drainage.
• Use the specified materials. Cheaper aggregates or filter media can cause premature failure, and for Section 104 adoption materials must comply with the DCG.
• Tell the adopting body before you cover drainage infrastructure, so it can inspect at key stages.

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

• Commission ground investigation, including BRE 365 percolation testing, check Environment Agency flood maps and consult the LLFA or SAB early.
• Engage a drainage engineer experienced in CIRIA C753. In Wales, ask the SAB for pre-application advice; in England, check the LLFA's local requirements.
• Discuss adoption with the water company (Section 104) and highway authority (Section 38) before you finalise the design, and in Wales prepare the SAB application.
• Discharge drainage conditions before starting work, protect SuDS areas from traffic and silt, and notify the adopting body before covering infrastructure.