HR: 09:15h
AN: H31H-05    [Abstracts]
TI: Hydrogeology of the Groundwater Dominated Williamson River Subbasin, Upper Klamath Basin, Oregon
AU: * Cummings, M L
EM: cummingsm@pdx.edu
AF: Dept of Geology, Portland State University, PO Box 751, Portland, OR 97207 United States
AB: Pyroclastic flow and fall deposits from the climactic eruption of Mount Mazama that formed Crater Lake influence flow paths for ground water migrating into the Williamson River sub-basin from relatively small catchments within the Cascade Range. Snow melt runoff in May and June partitions between low discharge (<1m³/s) surface streams and ground water. Pyroclastic flows have an estimated infiltration rate of 10^-4 to 10^-6 m/s. Ground water moves primarily through underlying pumice and weakly lithified, medium to coarse grained volcaniclastic sedimentary rocks and intertercalated thin basalt lava flows of Pleistocene age. Since April 2000 ground water levels have declined throughout the basin and the slope on the potentiometric surface between Klamath Marsh and the Cascade Range has steadily declined. The result is earlier (7/21/2001 versus 6/17/2004) and longer periods (126 days in 2001, 248 days in 2004/2005) of no surface discharge from Klamath Marsh to the Williamson River. Ground water discharge within Klamath Marsh is estimated for late summer when precipitation is absent, Williamson River discharge into the marsh is low (0.5 m³/s), discharge from the marsh is absent, and evapotranspiration is maximum. Based on a surface area of 62 km², the ground water discharge to Klamath Marsh is estimated at 3.1 to 3.7 x 10⁵ m³/day. During the growing season evapotranspiration is 110 to 120% of ground water discharge resulting in water level declines of nearly 1 m below the elevation at which surface discharge from the marsh resumes on the Williamson River.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
SC: Hydrology [H]
MN: Fall Meeting 2005