Onno Bokhove, Mark Kelmanson, Thomas Kent

The questions we address in the present article are the following:
(i) whether (extreme) river floods can be prevented or seriously mitigated by the introduction of beavers in the wild, and (ii) for which river catchments does flood mitigation by beaver activity (not) work?
By using the concept of flood-excess volume (FEV) for four rivers in the UK, in the context of five (extreme) UK flood events in the last two decades, we show that even a 10% flood reduction of the FEV, using beaver colonies and beaver dams, requires hundreds of such colonies per river catchment. Given the high number of beaver colonies and dams required for mitigation, we conclude/demonstrate that serious flood mitigation by massive introduction of beaver colonies is completely unrealistic, in stark contrast to statements made in scientific literature and in the media. Furthermore, FEV is valuable beyond its utility as a tool in analysing the efficacy of beaver dams as flood protection: it is demonstrated to be a useful tool for assessing in an easy-to-understand way a variety of flood-mitigation measures, including analysing the scalability of local flood-mitigation measures for overall catchment needs.