Aspect | Risk of Flooding from Surface Water (RoFSW) | Flood Zones 2 & 3 |
Type of flooding | Heavy rainfall, poor drainage, runoff from land, roads, roofs (flash flooding) | Rivers (fluvial flooding) and sea (tidal flooding) |
Source | Environment Agency surface water flood maps (rainfall & topography modelling) | Environment Agency Flood Map for Planning |
Probability bands | High (>3.3% annual chance), Medium (1–3.3%), Low (0.1–1%) | Zone 2: 0.1–1% (river) / 0.1–0.5% (sea)Zone 3: >1% (river) / >0.5% (sea) |
Scale | Very localised – property/street level | Strategic – floodplains and catchments |
Duration of flooding | Usually short-lived, flash flooding, drainage-dependent | Longer duration floods, river/sea overbank flooding |
Planning use | Risk assessments for property owners, drainage design, resilience measures | Core to planning policy (Sequential Test, Exception Test, Flood Risk Assessments) |
Examples | Water pooling in a street valley after heavy rain | Floodplain along the Thames or Severn rivers |
