Flood Risk and Surface Water Drainage in Enfield
Enfield has bespoke planning policies including level-for-level floodplain compensation and specific SuDS requirements for all developments including minor applications.
Flood Risk Assessments (FRA) in Enfield
The latest NAFRA2 report states “Over one quarter of properties in areas at high flood risk from surface water flooding are in London — nearly a third of a million.”
The London Borough of Enfield has several bespoke planning policies and numerous Critical Drainage Areas (CDAs) to navigate. Enfield can seem at first glance a problematic region to gain planning approval for your project. However, over the last 3 years, Aegaea has been involved with over 100 different projects minor through to major applications within the area.
In line with the Enfield Council’s Validation Checklist (updated in October 2024), you’ll need to provide a Flood Risk Assessment if the development involves any of the following constraints (this includes Minor Developments):
- Surface water flood risk (or in a CDA)
- Flood Zone 2, 3a, 3b
- Greater than 1ha
- Proposals including new buildings, basements, extensions to basements, extensions within 8m of a watercourse
What Should My Flood Risk Assessment in Enfield Include?
The specific advice listed in Enfield’s Validation Checklist includes:
- Finished Floor Levels to be set at least 150mm above the 1:100 Year Surface Water Flood Level (plus climate change)
- Finished Floor Levels to be set at least 300mm above the 1:100 Year Fluvial Flood Level (plus climate change)
- Level for Level Floodplain Compensation — if the development is located within either of the 1:100 Year Flood Level (plus climate change) for fluvial or surface water flooding. This is an important requirement as not all councils require Floodplain Compensation
- A Flood Management/Evacuation Plan must be provided demonstrating that the evacuation route is in the “Very Low Hazard Level”
- Flood resistant and resilient measures should be utilised where appropriate
Floodplain Compensation is when a section of the site (i.e. a small section of the garden) is lowered during construction to prevent any flood water displaced by the development increasing risk elsewhere.
Aegaea hold the Environment Agency’s modelled flood data for Enfield on file, including Enfield’s preferred datasets for the Pymmes Brook and Salmons Brook catchments which are considered superior to the national RoFSW mapping.
Sustainable Drainage Systems (SuDS)
Most if not all developments in Enfield are now required to demonstrate how surface water will be managed as part of the development, adhering to the London Plan Drainage Hierarchy:
- Store rainwater for later use
- Use infiltration techniques, such as porous surfaces in non-clay areas
- Attenuate rainwater in ponds or open water features for gradual release
- Attenuate rainwater by storing in tanks or sealed water features for gradual release
- Discharge rainwater direct to a watercourse
- Discharge rainwater to a surface water sewer/drain
- Discharge rainwater to the combined sewer
Recent updates from the Council at the end of 2024 indicate that minor developments (i.e. developments below 250m2 and all Householder developments) may only require their specific SuDS proforma to be completed, potentially saving on both time and cost.