Flood Risk Assessment Guide
What a Flood Risk Assessment is, when you need one, and what it should contain.
Last updated: 2026-03-26
What Is a Flood Risk Assessment?
A Flood Risk Assessment (FRA) evaluates the flood risk to a development site and demonstrates how flood risk will be managed now and over the lifetime of the development.
When You Need an FRA
- All development in Flood Zones 2 and 3
- Development on sites larger than 1 hectare in Flood Zone 1
- Development in an area with known drainage problems
- Where the EA or Lead Local Flood Authority has requested one
Types of FRA
Desktop FRA: Uses existing mapping and data. Suitable for low-risk sites. Costs £500-1,500. Detailed FRA: Includes hydraulic modelling, topographic surveys, and detailed mitigation design. Costs £2,000-10,000+.What an FRA Must Include
- Site description and location
- Assessment of all sources of flooding
- Existing flood risk (from EA mapping and historical data)
- Impact of climate change over the development's lifetime
- How surface water drainage will be managed
- Proposed mitigation measures
- Emergency access and evacuation routes
Climate Change Allowances
FRAs must account for increased flood risk due to climate change. The EA publishes climate change allowances — currently a 35% increase in peak river flows for most of England.