HR: 0800h
AN: OS21B-1223    [Abstracts]
TI: The Columbia River Estuary: Sediment Source or Sediment Sink? Process-based Modeling of Sand Transport and Morphological Change at a Dynamic River Mouth
AU: * Lesser, G
EM: glesser@usgs.gov
AF: Delft Hydraulics, Rotterdamseweg 185, Delft, 2600MH Netherlands
AU: * Lesser, G
EM: glesser@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, MS999 , Menlo Park, CA 94025 United States
AU: Gelfenbaum, G
EM: ggelfenbaum@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, MS999 , Menlo Park, CA 94025 United States
AU: Moritz, R
EM: Hans.R.Moritz@nwp01.usace.army.mil
AF: USACE Portland District, PO Box 2946, Portland, OR 97208 United States
AU: Kaminsky, G
EM: gkam461@ECY.WA.GOV
AF: Washington State Department of Ecology, PO Box 47600, Olympia, WA 98504 United States
AB: The Columbia River accounts for more than 75% of the coastal drainage on the U.S. West Coast and during the late Holocene has delivered O(15 Mm$^{3}$/yr) of sediment (sand and finer) to the coasts of Oregon and Washington. However, anthropogenic influences have modified both the river discharge and the transport of sand through the estuary to such an extent that it is no longer clear whether the Columbia River Estuary delivers sand to, or extracts sand from, the coastal system. This study applies a process-based three-dimensional numerical hydrodynamic and sediment transport model (Delft3D) to the transport of sediment in and around the mouth of the Columbia River. The primary objectives are to isolate which physical processes dominate the transport of sand in different regions of the river mouth and estuary and to understand how the dynamic balance between these processes determines whether the Columbia is currently a net source or sink of sand in the coastal system. Preliminary model results indicate that the balance between the physical processes that govern the transport of sand through the Columbia Estuary varies both spatially and temporally. At the upper end of the estuary river discharge dominates sand transport, with river floods accounting for the majority of sand delivered to the estuary. Through the estuary mouth density-driven estuarine circulation plays an important role in driving an inwards-directed flux of sand in the main channel. In the outer estuary mouth wave-driven currents and mass fluxes dominate sand transport and net transport patterns are largely determined by the coastal wind and wave climate. As such, the supply of sand to the upper estuary is dependent on temporal fluctuations in river discharge, whereas the transport of sand through the river mouth depends on the dynamic balance between river discharge, tidal range, and wave climate. Initial model results suggest that the river mouth fluctuates between importing and exporting sand-sized sediment.
DE: 4235 Estuarine processes
DE: 4255 Numerical modeling
DE: 4558 Sediment transport
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting