Summary
Risk of Flooding from Surface Water, or RoFSW, is a national model showing where rainwater may lie or flow when drainage systems are overwhelmed. It uses terrain modelling, drainage assumptions, local model enhancements where available and depth bands. Buyers must understand the modelling assumptions because a building footprint may look dry due to the modelled building uplift while a low threshold or basement could still be exposed.
Definition
RoFSW is England’s Risk of Flooding from Surface Water mapping. It shows surface water flood extents and depths for 3.3%, 1% and 0.1% annual probability rainfall events, with climate change information added in the updated mapping. The model uses a digital terrain model, applies drainage loss assumptions and raises buildings in the model to reduce false flooding of footprints. Very shallow water may also be removed from displayed mapping to reduce clutter. For buyers, RoFSW should be read with site levels, thresholds, gullies, kerbs, dropped drives, local sewer information and Lead Local Flood Authority evidence.