HR: 0800h
AN: H41A-0128    [Abstracts]
TI: Case Study: Channel-forming discharge on the Dolores River and Yampa River, Colorado
AU: * Richard, G A
EM: grichard@mesastate.edu
AF: Mesa State College, 1100 North Ave., Grand Junction, CO 81501, United States
AU: Anderson, R
EM: Rick.Anderson@state.co.us
AF: Colorado Division of Wildlife, Independent Ave., Grand Junction, CO 81501, United States
AB: Channel-forming discharges of both the Yampa and Dolores Rivers have been estimated in the past by various methods. In this study we estimated channel-forming discharge for three study sites on the Yampa River and Dolores River in Colorado via four different methods and compared the results with results from previous studies. The first method estimated the bankfull discharge utilizing GPS survey data, GIS mapping and HEC-RAS modeling to determine the flow that begins to inundate the floodplains or reaches the top of banks. The second method determined the effective discharge using discharge and sediment data at USGS gaging stations to determine the flow that transports to most sediment over a long period of time. The third method involved development of flood-frequency curves from annual peak flow data and determination of the two-year frequency flow. The final method estimated the flows necessary for marginal transport and for significant motion of the bed material using the Shields equation and the average boundary shear stress. On the Dolores River, the channel-forming discharge estimates are in the range of 74 to 96 m3/s corresponding to 1.8 to 2.5-year frequencies in the post-dam flow regime. The effective discharge was not estimated on the Dolores River because of a lack of sediment data. On the Yampa River, the flow that inundates most of the floodplain areas and the flow that begins to mobilize the bed material range from 311 to 368 m3/s corresponding to 2.5 to 5.4 year frequencies. The effective discharge on the Yampa River, however, was estimated to be 230 m3/s and 1.4-year frequency, which differs from previous studies that suggested that the bankfull and effective discharges are equivalent. The difference between estimates of bankfull and effective discharge on the Yampa River raises questions regarding which method is appropriate to estimate channel-forming discharge in a gravel- bed river.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting