Abstract
The Environment Agency has recently completed research looking at rainfall runoff assumption within national scale surface water flood mapping in England and Wales . In particular, the research focussed on the use of a single drainage rate parameter (x mm/hr) to represent the water removed by sub-surface drainage system. The research project developed a method for varying the drainage rate from the national default using local knowledge. We concluded that this approach was valid for the current generation of national scale flood maps. However, we also identified that there is very little scope to develop the approach further. Instead we suggest that new methods need to be developed to support future improvements to national scale surface water flood mapping.
Highlights
In England there are 3 million properties at risk from surface water flooding (Environment Agency 2014)
The drainage rates identified from local models were compared against seven different characteristics of the case study sites
The statistical approach identified the following drainage rates for each case study. These results can be compared to drainage rates extracted from local data, provided below
Summary
In England there are 3 million properties at risk from surface water flooding (Environment Agency 2014). The main simplification used in the uFMfSW is to parameterise the drainage network. We assume that a fixed 12 mm per hour of rainfall is removed by the drainage network. In England and Wales, the Updated Flood Map for Surface Water (uFMfSW) has been published. It provides flood depth and velocity information, at 2 metre resolution for a range of flood probabilities and storm durations. It aims to give a broad understanding of flood risk in an area rather than accurate property level risk assessments
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