This research project has developed new guidance to estimate local drainage rates when mapping and modelling surface water flood risk. The information can be used to validate and update the national maps, called the Risk of Flooding from Surface Water, which use a national average drainage rate.
The guidance provides simple approaches for Lead Local Flood Authorities to use to check if the national maps represent surface water flood risk in their area. The approaches can also be used to see how the flood maps may change with more or less drainage, and to test scenarios like future climate change.
This project proposes and tests approaches to estimate locally specific drainage rates. This will help users estimate the impact of any changes in drainage on the extent of potential flooding – and potentially inform investment decision-making.