Sediment Characterization of a drowned river valley: Foster Reservoir, Willamette Valley, Oregon
Nick Poser – MS candidate
Advisor: Dr. Jillian Maloney
GMCS 129 – August 5, 2022 at 9 am
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New Chirp data collected from Foster Reservoir shows the accumulation of sediment along a drowned river valley in the Willamette Drainage Basin in central Oregon. Two small mountainous rivers, the South Santiam River and the Middle Santiam River merge into the reservoir, where a portion of the streams’ bedload and sediment load are trapped. Results show that fine-grained suspended load is accumulated mostly in the deepest part of the reservoir at a maximum annual rate of 26 mm/yr. Bedload is deposited as a subaqueous delta from the South Santiam River, but minimal bedload deposition is observed from the Middle Santiam River, likely due to trapping by the upstream Green Peter dam. These results are important for reservoir management and for reducing environmental impacts of the dam. Additionally, drowned river valleys potentially contain archaeological sites that may be impacted by accumulating sediment load.