HR: 16:30h
AN: H32I-03    [PDF]
TI: Bed Mobility on the Deschutes River, Oregon: Tracer Gravel Results
AU: * Kondolf, G M
EM: kondolf@uclink.berkeley.edu
AF: Department of Landscape Architecture and Environmental Planning, 202 Wurster Hall University of California, Berkeley, CA 94720 United States
AU: Williams, J
EM: jgwill@dcn.davis.ca.us
AF: Independent consultant, 875 Linden Lane, Davis, CA 95616 United States
AB: The Deschutes River, drainage area 20,250 km2 near Madras, Oregon, is a gravel-bedded river, impounded since 1957 by three dams in the Pelton-Round Butte hydroelectric project, operated by Portland General Electric (PGE). Salmon spawning has declined in the reach below the dams since their construction, so possible project effects on spawning habitat are an issue of concern in relicensing of the project. Consultants to PGE applied the Parker bedload transport function to several sites below the hydroelectric dams; they concluded that the entrainment threshold flow was 340 m3s-1, and that the bed had been mobile only 25 days in the 72-year period of record from 1925-1996. However, their model was not calibrated with any actual field data of bed mobility or bedload transport, and the calculations were for full bed mobility, ignoring potentially significant bedload transport that might occur at a condition of partial mobility. To redress that lack of field data, we placed tracer gravels in the bed at three sites below the dams. In 2002 tracer gravels moved at one of the three sites after a flow of 150 m3s-1 (128-mm stones moved up to 1 m). The minor movement suggests that the bed is just beginning to move at 150 m3s-1, but indicates that the previously assumed entrainment threshold of 340 m3s-1 is too high.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1857 Reservoirs (surface)
SC: Hydrology [H]
MN: 2003 Fall Meeting