Hydrogeomorphic effects of beaver dams in Glacier National Park, Montana

Sediment depth and stream-flow data from 10 beaver ponds illustrate that be avers (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 substant ially increase with dam age. Beaver impoundments also reduce the velocity a nd discharge of streams emerging downstream of dams. Older beaver dams more efficiently reduce stream velocity and discharge than young dams. Three ol der dams actually precluded downstream discharge, redistributing water as h yporheic outflow. The ability of beavers to alter the hydrogeomorphic envir onment 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.