HR: 17:00h
AN: H54B-05    [Abstracts]
TI: Simulating Sub-Decadal Channel Morphologic Change in Ephemeral Stream Networks
AU: * Semmens, D J
EM: semmens.darius@epa.gov
AF: U.S. EPA Office of Research and Development, P.O. Box 93478, Las Vegas, NV 89193
AU: Osterkamp, W R
EM: wroster@usgs.gov
AF: Desert Laboratory, U.S. Geological Survey, 1675 W Anklam Rd., Tucson, AZ 85745
AU: Guertin, P
EM: phil@nexus.srnr.Arizona.EDU
AF: School of Natural Resources, University of Arizona, 325 Biological Sciences East, Tucson, AZ 85721
AU: Goodrich, D C
EM: dgoodrich@uswcl.ars.ag.gov
AF: Water Conservation Lab, USDA Agricultural Research Service, 4331 E Broadway Rd., Phoenix, AZ 85040
AB: A distributed watershed model was modified to simulate cumulative channel morphologic change from multiple runoff events in ephemeral stream networks. The model incorporates the general design of the event-based Kinematic Runoff and Erosion Model (KINEROS), which describes the processes of interception, infiltration, surface runoff, and erosion from small watersheds predominantly characterized by overland flow. A geomorphic sub-model was added to compute geometric adjustment of the channel reaches in response to computed changes in sediment storage by minimizing the total stream power. The event-based watershed model framework permits exceptional temporal resolution of channel response to ephemeral water and sediment fluxes, including impacts resulting from distributed land-use/cover management. A GIS-based interface was developed to facilitate parameterization of the model, track cumulative geomorphic change and errors resulting from multiple distributed rainfall events. In addition the interface allows visualization of the spatial patterns of computed geomorphic adjustment, and permits comparisons of results from different simulations. Results from multiple-event simulations indicate that morphologic adjustment within channel networks is predominantly controlled by the frequency and magnitude of rainfall events. In ephemeral stream networks transmission losses progressively decrease the transport capacity of flows as they move downstream. Drier periods, characterized by small runoff events, thus produce aggradation and increasing width-to-depth ratios within the smallest headwater channels. As rainfall and the number of large events increases, headwater channels begin to incise and sediment is progressively redistributed further downstream. Disturbance within a portion of the watershed can interfere with this response pattern, with significant alterations to channel morphology extending well downstream of the disturbance. Comparisons of simulated patterns of morphologic adjustment with and without localized urbanization demonstrate the anticipated geomorphic response of incision within the urbanized area and increasing width-to-depth ratios downstream.
DE: 1812 Drought
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting