Impacts of beaver dams on channel hydraulics and substrate characteristics in a mountain stream

Beaver dams have significant impacts on the hydrology, temperature, biogeochemical processes, and geomorphology of streams and riparian areas. They have also been used as a viable tool in restoring impaired riverine systems. Because of the dynamic nature of beaver dams, these influences vary and are difficult to quantify. To begin understanding the impacts of beaver dams in mountain streams, we developed 1D hydraulic models for a beaver impacted reach that includes eight dams and a non-impacted reach to compare hydraulic responses (e.g. channel depth, width, and velocity distributions). We also compared observations of substrate size distributions for different geomorphic/habitat units within each reach. Results from the models indicated shifts in channel hydraulics through statistically significant increases in depths and widths as well as a decrease in flow velocities through the beaver impacted reach. These hydraulic adjustments, as a result of beaver dams, are consistent with observed changes in the increased variability and spatial heterogeneity in sediment size distributions. Through the application of three different modelling approaches, we found that a relatively low number of beaver dams would result in significant changes in channel hydraulics. These results provide preliminary information regarding the number of dams per unit stream length required to begin meeting various restoration goals.