HR: 1340h
AN: H53B-1242    [Abstracts]
TI: Relationships between River Discharge and Stream Bed Scour: Implications for Redd Scour on a Large Regulated River
AU: * Lang, M
EM: mml1@humboldt.edu
AF: Humboldt State University, Environmental Resources Engineering, Arcata, CA 95521 United States
AU: May, C
AF: University of California, Berkeley, Dept of Earth and Planetary Sciences, Berkeley, CA 94720-4767 United States
AU: Smith, B
AF: USFS Pacific Southwest Research Station, 1700 Bayview Drive, Arcata, CA 95521 United States
AU: Lisle, T
AF: USFS Pacific Southwest Research Station, 1700 Bayview Drive, Arcata, CA 95521 United States
AU: Castelanelli, C
AF: Humboldt State University, Environmental Resources Engineering, Arcata, CA 95521 United States
AB: A critical knowledge gap for implementing environmental flow releases on regulated rivers is understanding the effects of dam releases on the potential for scouring of spawning redds in downstream reaches. To address this question we need to understand the relationships between river discharge, bed mobility, and scour depth in river reaches heavily utilized by spawning salmon. Once these relationships are established it will be possible to calculate the probability that dam releases and/or tributary generated floods will result in a significant level of egg/embryo mortality. Our approach couples numerical modeling and empirical data to quantify spatially explicit predictions of bed mobility and identify specific areas where scour is deep enough to impact redd viability. Boundary shear stress values are predicted using the USGS's Multi-Dimensional Surface Water Modeling System (Nelson and Smith, 1989) for a segment of the Trinity River below Lewiston Dam. From model-generated shear stress and mapping of local particle size distributions, Shield stress parameters are determined to quantify areas of differential bed mobility. Field data acquired during high flow events is used to calibrate the model and to obtain estimates of scour depth. Scour depth is measured using a dense array of scour chains supplemented by motion-sensing radio tagged particles that record the specific time, and hence discharge, that particles in the surface and subsurface layer become mobile. Zones of differential mobility are compared with detailed maps of spawning sites for Chinook to quantify risk of significant redd scouring and to determine whether salmon are spawning in areas of inherently high or low mobility.
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
DE: 1857 Reservoirs (surface)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting