Highlights

The key new finding of this study was a strong modulating effect of soil permeability on the hydrological effects of beaver dams. By changing the behaviour of an artificially incised stream from draining floodplain soils to partially irrigating them, beaver dams could help to restore floodplain wetland hydrology well beyond beaver ponds themselves.

Model simulations showed that this effect was substantially greater with permeable floodplain soils and reduced with relatively impermeable soils. Model simulations of the main study site (Garage Field and surroundings) suggested that beaver dams caused a 32% increase in the area that had floodplain water levels (principally water table levels) high enough for a common wetland plant in the study area (Glyceria maxima). This “irrigation” came at the expense of slightly decreased downstream flows due to the water diverted onto the floodplain. Therefore, beavers have significant potential to restore hydrological conditions to headwater streams and floodplains that have been artificially drained thus supporting wetland restoration.