Modelling the impact of beaver dams on hydrological extremes following the re-introduction of beavers in England 

Abstract

The Eurasian beaver (Castor fiber) is being reintroduced to Great Britain after an absence of ~400 years. Beavers are well known for their considerable engineering capabilities. Given the right conditions, beavers construct dams, excavate channels and maintain wetlands. These changes have been demonstrated to have a significant impact upon hydrological extremes in the English environment. There is the potential for beaver re-introduction to have a transformative impact as a widespread nature-based solution (NBS). However, there is a need for policy and management relevant understanding at a national level. Funded by the Environment Agency in England, the aim of this study was to use a modelling approach to be able to estimate how catchments in England may respond to extreme events following the re-introduction of beavers. To accomplish this, we have applied the 2D version of the hydraulic model HEC-RAS to sites across England. Sites were selected that had the potential for beavers to construct dams. Beaver dams are represented within HEC-RAS by digitising a series of weirs intersected by culverts, allowing water to leak through the dam as well as overtopping the weir. To account for uncertainty in dam properties, we configured the model to simulate different configurations of dam height, as well as the “leakiness” of each dam. Using the approach described, HEC-RAS was used to simulate the impact of hypothetical beaver dams on storm events of different magnitudes in addition to low flow scenarios. Results suggest that the impact of beaver dam sequences on hydrology is highly dependent on channel and floodplain topography. We were then able to apply these results to produce an estimation of the impact of beavers on flow regimes at any river stretch in England. This was estimated for three scenarios with high, moderate and low presence of beavers across England. It is hoped that these modelling tools can be used to strategically determine where and how beavers may be able to provide a hydrological NBS and where supporting their wetland creation could be most valuable.