Hydrogeomorphic effects of beaver dams in Glacier National Park, Montana

Sediment depth and stream-flow data from 10 beaver ponds illustrate that beavers (Castor canadensis) considerably influence hydrogeomorphic processes in low-order stream systems of Glacier National Park (CNP), Montana. Beaver ponds clearly trap sediment, and the depth and volume of sediment substantially increase with dam age. Beaver impoundments also reduce the velocity and discharge of streams emerging downstream of dams. Older beaver dams more efficiently reduce stream velocity and discharge than young dams. Three older dams actually precluded downstream discharge, redistributing water as hyporheic outflow. The ability of beavers to alter the hydrogeomorphic environment in the near vicinity of their ponds is dramatic, but future work is still needed to elucidate the relative importance of lowered stream energy versus the erosive potential of underloaded water downstream.