HR: 1340h
AN: H33C-0475    [Abstracts]
TI: Geology Broadly Predicts Summer Streamflow in Volcanic Terrains: Lessons From the Oregon Cascades
AU: * Jefferson, A
EM: jeffersa@geo.oregonstate.edu
AF: Dept. of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: Grant, G
EM: gordon.grant@orst.edu
AF: USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR 97331 United States
AU: Lewis, S
EM: sarah.lewis@orst.edu
AF: Dept. of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, OR 97331 United States
AU: Tague, C
EM: ctague@mail.sdsu.edu
AF: Dept. of Geography, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4493 United States
AB: The western slope of the Cascade volcanic arc is comprised of two distinct geologic provinces, both with similar climate and vegetation, making it an excellent place for examining geologic controls on hydrologic variability. Analysis of streamflow from USGS gauges has shown that summer streamflow characteristics are related to the percent of basin area underlain by High Cascade (0-7 Ma) basalt flows and related rocks. Watersheds with High Cascade geology exhibit higher unit streamflows and slower summer recessions than those with Western Cascade (7-40 Ma) geology. Since July 2003, gauging of thirteen 1st to 4th order High Cascade streams in the McKenzie River basin has shown that some High Cascade streams are runoff-dominated, like Western Cascade streams, while others are fed by large volume cold springs, with relatively steady flow. During the summer, these spring-fed streams provide over 80% of the flow to the McKenzie River. In winter months, runoff-dominated streams respond rapidly to rain and rain-on-snow events and become the major water source to the McKenzie River. Spring-fed streams also respond to precipitation events, but show muted and delayed hydrograph peaks. Summer flow behavior and response to individual events varies between springs, even between those that are located less than 1 km from each other. Oxygen isotope analysis suggests that closely spaced springs may have recharge areas differing by over 150 m in average altitude. These springs emanate from lava flow toes or contacts; thus, paleotopography, including buried channel networks, and lava flow characteristics, such as primary and secondary porosity, are also likely to be important determinants of event and seasonal streamflow response. Therefore, geologic differences are useful for predicting streamflow in large basins and over seasonal to interannual timescales, but at the headwater catchment spatial scale, or event time scale, groundwater-fed streams exhibit variability that cannot be predicted by regional geology alone. Prediction at these scales will require more detailed knowledge of local geologic and meteorologic variability.
DE: 1829 Groundwater hydrology
DE: 1860 Runoff and streamflow
DE: 1884 Water supply
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting