Risk of Flooding from Surface Water - Speed

Risk of Flooding from Surface Water (RoFSW) map is an assessment of where surface water flooding may occur when rainwater does not drain away through the normal drainage systems or soak into the ground, but lies on or flows over the ground instead. It is produced using national scale modelling and enhanced with compatible, locally produced modelling from lead local flood authorities (LLFAs). The RoFSW datasets include information about flooding extents, depths, speed and hazards.

This dataset shows information about flood speed. The speed of water during a flood is an important factor in how dangerous a flood might be.

RoFSW is a probabilistic product, meaning that it shows the overall risk, rather than the risk associated with a specific event or scenario. In externally published versions of this dataset, risk is displayed as one of three likelihood bandings:

High - greater than or equal to 3.3% (1 in 30) chance in any given year; Medium - less than 3.3% (1 in 30) but greater than or equal to 1% (1 in 100) chance in any given year; Low - less than 1% (1 in 100) but greater than or equal to 0.1% (1 in 1000) chance in any given year.

Note that all locations outside of mapped extents should be considered at ‘Very Low’ risk. ‘Very Low’ extents in the dataset have been explicitly modelled as below 1 in 1000 chance.

This speed dataset shows the likelihood of a flood occurring with water travelling at a given speed (or higher). There are separate layers with thresholds for speeds of 0m/s (i.e. flooding extent), 0.25m/s, 0.5m/s, 1m/s and 2m/s.