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.