Sustainable drainage systems

Enfield is both a Lead Local Flood Authority (LLFA) and a statutory consultee for major planning applications in relation to surface water drainage. As such, we have certain requirements for all planning applications of this kind.

The first is that you submit a Sustainable Drainage Strategy that demonstrates how Sustainable Drainage Systems (SuDS) will be used to manage rainfall runoff.

The second requirement is that, if the development is in a flood risk area, you submit a Flood Risk Assessment. This is to ensure that new development is safe from flooding, does not increase flood risk elsewhere and reduces overall flood risk.

Email the Structures and Watercourses team if you have any queries.

Sustainable Drainage Strategy

A Sustainable Drainage Strategy details how surface water runoff and waste water arising from the development of a site will be managed in line with the Development Plan. See our Development Management Document (DMD) for further information, particularly DMD policies 59 to 62.

What a Sustainable Drainage Strategy should include

A Sustainable Drainage Strategy should include the following:

  • A plan of the existing site
  • A topographical plan of the area
  • Plans and drawings of the proposed site layout identifying the footprint of the area being drained (including all buildings, access roads and car parks)
  • The controlled discharge rate for a 1 in 1 year event and a 1 in 100 year event (with an allowance for climate change), this should be based on the estimated greenfield runoff rate
  • The proposed storage volume
  • Information on proposed SuDS measures with a design statement describing how the proposed measures manage surface water as close to its source as possible and follow the drainage hierarchy in the London Plan
  • Geological information including borehole logs, depth to water table and/or infiltration test results
  • Details of overland flow routes for exceedance events
  • A management plan for future maintenance

Flood Risk Assessment

A Flood Risk Assessment considers the possible impacts of all sources of flooding on a new development – this includes river flooding and surface water flooding.  It must demonstrate that the development is safe and does not increase flood risk elsewhere.  Refer to the DMD and Enfield’s Strategic Flood Risk Assessment for additional information about requirements for site-specific Flood Risk Assessments.

Our Local Flood Risk Management Strategy page has more information, and the Environment Agency’s online flood maps has information about the extent of flood risk.

What a Flood Risk Assessment should include

Refer to Appendix 10 of the DMD for a description of the minimum requirements for a site-specific Flood Risk Assessment.