To What Extent Might Beaver Dam Building Buffer Water Storage Losses Associated with a Declining Snowpack?

Dam building activity by North American Beaver (Castor canadensis) alters the timing and delivery of stream water and facilitates groundwater infiltration, overall increasing natural water storage behind and adjacent to dams. At the stream reach scale, increased water storage often alters hydrologic regimes by attenuating annual, and storm-event hydrographs, and increasing base flows. In the montane west, the most important water storage reservoirs are not human-made dams, but mountain snowpack, which slowly releases water through a mix of runoff and infiltration. Given estimates of decreasing snowpack with warming temperatures, beaver dams could provide a conceptually similar function to snowpack by delaying the delivery of precipitation by increasing surface and groundwater storage, thus lengthening residence time as water travels downstream. However, lack of predictive methods for modeling storage increases associated with relatively small magnitude beaver ponds at large spatial scales has precluded further investigation of this hypothesis. I address this knowledge gap by supplementing existing empirical data regarding the height of beaver dams and implement these empirical height distributions to develop the Beaver Dam Surface Water Estimation Algorithm (Chapter 2), a predictive model estimating beaver pond water storage that can be applied spatially at large scales. I then apply this model to estimate potential surface water storage and parameterize a groundwater model to estimate resulting groundwater storage increases for the entire Bear River basin under four different beaver dam capacity scenarios (Chapter 3). Estimated water storage changes from beaver dams are presented in the context of expected reductions in average annual maximum snow water equivalent, and existing and proposed reservoir storage within the basin. While the water storage provided by beaver dams is only a small fraction of expected snow water equivalent loss, it is not insubstantial and may prove beneficial for ecosystems where human-made reservoirs are not available to regulate hydrologic regimes. These results also stress the importance of further research examining how the cumulative effects of dams may affect the timing of runoff under changing precipitation regimes