HR: 1330h
AN: H52A-1162    [PDF]
TI: Preliminary analysis of water discharge and suspended sediment data from the Columbia River Basin: shifting rating curves and diminishing sediment loads
AU: * MacGregor, K R
EM: macgregor@macalester.edu
AF: USGS Coastal and Marine Geology, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Gelfenbaum, G
EM: ggelfenbaum@usgs.gov
AF: USGS Coastal and Marine Geology, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Rubin, D
EM: drubin@usgs.gov
AF: USGS Coastal and Marine Geology, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Significant erosion along the coastlines of southwestern Washington in the last decade has motivated increased studies of sediment sources, sinks, and transport dynamics in the region. A key question is whether a reduction in sediment supply is responsible for the recent shift from a depositional regime. Because the Columbia River is the major fluvial system in the littoral cell, it is important to quantify sediment flux from the Columbia River to the coastal environment. We examine historical records of water discharge and suspended sediment transport along the Columbia main stem and in three subbasins in an attempt to quantify changes in total sediment transport and total load, and examine possible shifts in sediment sources over time. Suspended sediment data from the main stem near Vancouver, WA demonstrate a 3 to 5 fold downward shift in the rating curve in the last 90 years. The same trend is visible in data from the Snake River, with a decrease of almost an order of magnitude in sediment transport since the 1950's. Grain size data from the Kootenai River show a clear fining trend in the suspended load. The John Day River is the only long-term record we examined with no change in the rating curve over time; it is also the largest undammed river in the basin. Calculations of sediment load in the main stem were made using actual water discharge, estimated discharge (assuming no dams), and calculated `virgin' flow (Naik and Jay, in review). Preliminary results suggest that changes in the hydrograph (assuming a uniform rating curve) would diminish sediment transport to the coast by up to 20% over the last century; changes in the rating curve are responsible for at least that change, possibly more.
DE: 1655 Water cycles (1836)
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 3020 Littoral processes
SC: Hydrology [H]
MN: 2003 Fall Meeting