Natural Flood Management – how much can it help nationally? Floods in the winter of 2019-20 sparked a lot of discussion on whether our focus in managing risk should shift from traditional defences to embrace natural flood management – using techniques to improve soil properties, slow the flow of water in catchments, leaky dams etc to reduce fluvial flows and hence risk. These are popular with the public as they appear to offer a win-win – improving the environment while reducing risk. But how effective can they be at managing national flood risk? Some recent research by Dadson et al. synthesizing evidence from a wide range of sources sounds a note of caution, finding that the impacts of NFM will be mainly limited to more frequent floods in smaller catchments (expressed in their figure, right). How much risk is there from frequent floods in small catchments? We started to think about this for England by analysing postcode data (here, used as a proxy for property level data) along with the Environment Agency’s Risk of Flooding from Rivers and the Sea dataset (here) and the UK Centre for Ecology and Hydrology’s integrated hydrological units data (here). The analysis is limited to fluvial risk, so postcodes below 10m above sea level (according to Ordnance Survey’s Terrain 50 data) are removed to filter out coastal flood risk. Results are in the tables below. The table on the left shows the number of properties in each flood risk band by catchment size. Most properties are in the medium/low bands, and most are in catchments greater than 100 km2 in area. In terms of property counts, the areas that could benefit most from NFM (high probability band, cover only around 4% of the total properties at fluvial risk. Counts of properties at risk don’t tell the full story, as properties which flood more frequently will contribute more to damages and disruption.

Click here to read more