Flood risk is a material consideration in planning. For developers and land agents, knowing which zone a site sits in — and what that actually means — is essential for early-stage screening.

Flood zone definitions (England & Wales)

Flood zones are based on Environment Agency (EA) mapping. They reflect the chance of river or sea flooding in a given year (annual probability).

- Zone 1 — Low risk: less than 0.1% annual probability (1 in 1,000 years). No EA flood map normally required for planning in many cases, but check local policy. - Zone 2 — Medium risk: between 0.1% and 1% (1 in 100 years). A Flood Risk Assessment (FRA) is typically required. - Zone 3a — High risk: 1% or greater (1 in 100 years or more). FRA required; sequential and exception tests may apply. - Zone 3b — Functional floodplain: land that would store or convey floodwater in a 1 in 100 year event. Development is heavily restricted.

Surface water (pluvial) flooding

Separate from river/sea zones, surface water (rainfall) flooding is mapped by the EA and by lead local flood authorities. It can affect sites in Zone 1. Always consider both when screening.

What developers should do

1. Screen early — Check zone and surface water as part of your first pass. Zone 3a/3b or significant surface water risk is often amber or red in a site pack. 2. Don't assume Zone 1 is clear — Local drainage, SuDS, and surface water can still be an issue. Use a report that includes both flood zone and surface water layers. 3. Use cited data — Your report should state the data source (e.g. EA Flood Map for Planning) and date. Never rely on unsourced "low/medium/high" labels. 4. Confirm with an FRA — A site screening report is not an FRA. For sites you're taking forward, commission a proper assessment.

Limitations

EA data is updated periodically; there can be lag after major changes. Small watercourses may not be fully reflected. When in doubt, check the official EA Flood Map for Planning and involve a flood consultant for marginal sites.

SiteSift pulls flood zone and surface water data into every report, with clear source citations. Use it to flag risk early, then follow up with specialist advice where needed.