HR: 1330h
AN: H42E-1122    [PDF]
TI: Debris Flow Initiation and Fan Reworking in the Green River Canyons of the Eastern Uinta Mountains: The Limited Role of Wildfire and the Significance of Low-Magnitude Floods
AU: * Larsen, I J
EM: isaaclarsen@cc.usu.edu
AF: Geology Department, 4505 Old Main Hill, Logan, UT 84322-4505 United States
AU: Schmidt, J C
EM: jschmidt@cc.usu.edu
AF: Department of Aquatic, Watershed, and Earth Resources, 5210 Old Main Hill, Logan, UT 84322-5210 United States
AU: Pederson, J L
EM: bolo@cc.usu.edu
AF: Geology Department, 4505 Old Main Hill, Logan, UT 84322-4505 United States
AU: Martin, J A
EM: jmartin@eaest.com
AF: EA Science and Technology, 6731 Collamer Road, East Syracuse, NY 13057 United States
AB: The primary determinant on channel organization of the Green River in the canyons of the eastern Uinta Mountains is the occurrence and frequency of debris flows in tributary watersheds. The frequency of these debris flows appears to be related to climatic factors, not factors related to wildfire. Debris flows in the eastern Uinta Mountains occur by a process known as the firehose effect, wherein overland flow generated on bedrock slopes cascades down steep cliffs and saturates and impacts colluvium stored in bedrock hollows. The colluvium fails, initiating debris flows that travel downslope to the Green River. The dry climate and high-strength bedrock cause hillslopes to be weathering-limited, prohibiting the formation of extensive regolith and vegetative cover. This reduces the degree vegetation regulates geomorphic processes and, in turn, causes wildfire to have little influence on debris flow initiation; slight increases in watershed runoff do not appear to alter the likelihood of this process occurring. A secondary determinant on channel organization in debris fan-dominated canyons are the magnitude of mainstem discharges and the degree to which they rework debris flow deposits; in this case flows are regulated by Flaming Gorge Dam. Substantial reworking of debris flow deposits can be accomplished by mainstem floods with discharges greater than 75%\ of the pre-dam two year flood, whereas floods with magnitudes less than 40%\ of the pre-dam 2-year flood do little reworking.
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting