What Is a Flood Risk Assessment? And What Do All the Flood Zones Mean?
A guide to Flood Risk Assessments in the planning system, covering when they are required, how the four EA flood zones work, and vulnerability classifications.
When FRAs Are Required
A Flood Risk Assessment (FRA) is essential for planning applications, with requirements varying based on development type and location. According to the National Planning Policy Framework, “site-specific flood risk assessments should be provided for all development in Flood Zones 2 and 3.”
The NPPF mandates FRAs for developments in Flood Zones 2 and 3, plus all proposals of 1+ hectares in Flood Zone 1 that meet specific criteria. An adequate FRA must assess risks from all flooding sources and demonstrate management strategies throughout the development’s lifetime.
The Four EA Flood Zones Explained
Flood Zone 1 (Lowest Risk): Less than 1 in 1,000 annual probability of flooding. Most development types are permitted without necessarily requiring an FRA.
Flood Zone 2 (Medium Risk): Between 1 in 100 and 1 in 1,000 annual probability of river flooding. An FRA is mandatory for planning applications.
Flood Zone 3a (High Risk): Greater than 1 in 100 annual probability of river flooding or 1 in 200 for sea flooding. FRAs are required.
Flood Zone 3b (Functional Floodplain): Approximately 1 in 20 annual flooding probability. Development is typically restricted, though exceptions exist.
Vulnerability and Risk Assessment
The planning system uses risk-based assessment where vulnerability classifications determine permitted locations. Housing is categorised as “more vulnerable,” while commercial spaces are “less vulnerable” — unless they contain hazardous materials.
Development compatibility depends on both flood zone designation and use vulnerability. Exception tests may be necessary to authorise certain projects.