Portland State University. Department of Geology
Michael L. Cummings
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geology
Hydrogeology -- Oregon -- Williamson River Watershed, Paleohydrology -- Oregon -- Williamson River Watershed, Williamson River (Or.)
1 online resource (116 pages)
Stress on the water resources of the Williamson River basin has led to their regulation to protect important habitat. Quantification of this resource is required for accurate regulation. A portion of this study is a hydrogeologic reconnaissance that suggests directions for future work. Measured discharge and deuterium isotope data from points above and below the Williamson River canyon indicate that the river receives 99% of its discharge from ground water during periods of low flow. The principle aquifer of the southern Klamath Marsh is a fractured basalt, while continental sediments that are up to 200 m thick provide high artesian yields south of the canyon. The disparity between high precipitation on the basin's western margin and the low and variable discharge of the Williamson River at the Kirk Sill suggests either the presence of a fault zone that interrupts the flow of ground water or deep flow paths that do not surface within Klamath Marsh.
Three terraces line the eastern edge of Klamath Marsh at approximate elevations of 1380, 1385, and 1397 m. The lowest terrace is late Holocene and cut into marsh sediment and reworked deposits from the pyroclastic eruptions of Mount Mazama. The middle terrace is planed into bedrock and formed when Pleistocene Lake Chemult occupied this basin. The upper terrace, a strand line, is delineated by a slope break that separates reworked pyroclastic deposits from undisturbed pyroclastic fall. Formation of this terrace occurred when pyroclastic flows from the cataclysmic eruption of Mount Mazama formed a blockage in the Williamson River canyon. Resultant backflooding reworked pyroclastic deposits and rafted pumice up to an approximate elevation of 1400 m. The blockage failed catastrophically from overtopping, draining 5.7 x 109 m3 of water, scouring the canyon and producing an erratic boulder deposit at the mouth of the canyon. Upstream evidence of rapid draining includes linear scour channels incised in pyroclastic-flow deposits and scouring of the broad Pleistocene terrace. Paleohydraulic reconstruction of down stream flooding using a flow-competence equation and a physically based dam-break model yield a peak discharge of 1.3 x 104 m3 s-1.
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Conaway, Jeffrey Scott, "Hydrogeology and Paleohydrology in the Williamson River Basin, Klamath County, Oregon" (1999). Dissertations and Theses. Paper 6378.