London Borough of Sutton Local Flood Risk Policies

The London Borough of Sutton adopted its local plan in 2018, covering the period from 2016 to 2031. Policy 32 specifically addresses flood risk and drainage.

Flood Risk Management

Policy 32 requires that developments avoid or minimise all sources of flood risk by:

• Preparing site-specific flood risk assessments for all proposals in Flood Zones 2 or 3, all major proposals in Flood Zone 1 over 1 hectare, and any proposal in critical drainage areas
• Avoiding inappropriate development in flood risk areas using the sequential and exceptions tests
• Setting buildings back at least 8 meters from main river banks and 5 meters from ordinary watercourses
• Ensuring “more vulnerable” and “highly vulnerable” developments within Flood Zones 2 and 3 maintain finished floor levels a minimum of 300mm above the modelled 1 in 100 annual probability flood level, including climate change
• Mitigating residual risks through flood resistance or resilience measures

Sustainable Drainage (SuDS)

Minimum SuDS performance standards include:

For greenfield sites: Peak runoff rates and volumes for the 1 in 100-year rainfall event must not exceed greenfield runoff rates for the same event.

For previously developed sites: Peak runoff rates and volumes for the 1 in 100-year event should achieve greenfield runoff rates unless demonstrably impractical. In such cases, runoff rates must not exceed 3 times the calculated greenfield rate per the Mayor’s Sustainable Design and Construction SPG. Site drainage strategies must contain the 1 in 30-year event plus climate change without flooding, with any overflow between the 1 in 30 and 1 in 100-year events safely contained on-site.

Sutton’s Policy 32 requires flood risk assessment applicants to also produce a SuDS strategy or SuDS statement for smaller developments.