HR: 0830h
AN: H41D-1025    [PDF]
TI: The Effect of Geomorphic Complexity on Water Temperature in a Pacific Northwest Alluvial River
AU: * Arrigoni, A S
EM: arrigoni@geog.ucsb.edu
AF: Department of Geography and ICESS, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Poole, G C
EM: gpoole@eco-metrics.com
AF: Eco-Metrics, 4051 Wildflower lane, Tucker, GA 30084 United States
AU: Thomas, S A
EM: sthomas@eco-metrics.com
AF: Eco-Metrics, 325 SW 3rd, Pendlton, OR 97801 United States
AU: Woessner, W W
EM: gl_www@selway.umt.edu
AF: Department of Geology, University of Montana, Missoula, MT 59802 United States
AU: Mertes, L A
EM: leal@geog.ucsb.edu
AF: Department of Geography and ICESS, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: Boer, B R
EM: brian.boer@umontana.edu
AF: Department of Geology, University of Montana, Missoula, MT 59802 United States
AU: O'Daniel, S J
EM: ScotODaniel@ctuir.com
AF: Department of Geography and ICESS, University of California Santa Barbara, Santa Barbara, CA 93106 United States
AU: O'Daniel, S J
EM: ScotODaniel@ctuir.com
AF: Confederated Tribes of the Umatilla Indian Reservation, PO Box 638, Pendleton, OR 97801 United States
AB: Hyporheic exchange of ground and surface water is an important physical process that contributes to the habitat template of alluvial rivers and is known to increase thermal diversity within streams by creating localized or isolated pockets where water temperature is buffered. Although the Umatilla River in northeastern Oregon, USA once supported healthy populations of salmonids (trout, salmon, and charr), summertime water temperatures in the river are now stressful or lethal to salmonids, exceeding 26$\deg$C. Using funding from NASA, the Confederated Tribes of the Umatilla Indian Reservation are coordinating the Data Rich Decision Support Environment research project to study the hydrologic and thermal regime of the river. As part of that study, we are documenting the influence of near-channel hyporheic exchange on the river's thermal regime. We instrumented a variety of stream channel units (pools, riffles, spring channels, etc.) and gravel bars with more than 70 temperature loggers. These were used to describe the thermal diversity of the channel and hyporheic zone in geomorphically complex settings where hyporheic exchange is prevalent. The loggers were deployed over a 4-week period during July and August. To monitor surface water temperatures loggers were attached to rebar that was pounded into the stream bed. For monitor hyporheic water temperatures loggers were placed in piezometers set 15 cm to 2 m into gravels . A total station was used to survey bar and streambed topography along with the locations of the temperature loggers. Resulting data suggest that complex channel patterns and bed-forms create hydraulic gradients within the near-channel aquifer that enhance hyporheic exchange. In addition to creating the expected localized patterns of thermal diversity in the stream channel near upwelling water, our data suggest that the cumulative affect of geomorphically complex nodes within the river have the ability to buffer diel temperature variation in the main flow of the river. Thus, when daily maximum temperature occurs and fish are most stressed by warm water temperatures, hyporheic exchange creates cool pockets of water and appears to reduce peak temperatures throughout the river. Our results suggest that loss of geomorphic complexity within the river due to flood-plain development, large wood removal, and channel engineering (e.g., dredging and diking) may reduce the effect of hyporheic flow as an important temperature regulation mechanism throughout the river. Restoration of geomorphic complexity and the fluvial processes that create and maintain geomorphic complexity may be an important step in restoration of habitat for now beleaguered runs of salmon within the river.
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
SC: Hydrology [H]
MN: 2003 Fall Meeting