HR: 17:25h
AN: H34A-06    [Abstracts]
TI: A tale of two rivers: channel adjustments to restorative floods in the Green River in Dinosaur N.M. as compared to those in the Colorado River in Grand Canyon N.P.
AU: * Alexander, J S
EM: frles25@yahoo.com
AF: Utah State University - Department of Watershed Sciences, 5210 Old Main Hill, Logan, UT 84322-5210, United States
AU: Schmidt, J C
EM: jack.schmidt@cc.usu.edu
AF: Utah State University - Department of Watershed Sciences, 5210 Old Main Hill, Logan, UT 84322-5210, United States
AB: Sediment mass balance is a critical system attribute in assessing the potential for restoration of dam-impacted rivers. We compared channel response to large floods on the Green River in Lodore Canyon to similar changes measured along the Colorado River in part of Grand Canyon National Park, a reach with similar geomorphic organization, regulatory constraints, and habitat management goals. The post-dam sediment mass balance of the Green River is indeterminate or in surplus, but the mass balance of the Colorado River is in deficit. Analysis of repeat measurements at 36 cross sections along a 20 km reach of Lodore Canyon show that the sand storage condition in 2006 was no different than the condition observed in 1994, despite an increased frequency of high magnitude floods. Four high magnitude floods occurred in 1997, 1999, 2005, and 2006, but only one, the 1999 flow, triggered channel adjustments to the bed and banks that were significantly different than those of the post- dam 2-year return flood. This condition of relative equilibrium contrasts the sand storage condition of the Colorado River in Grand Canyon, where sand bar area and volume have declined despite specific dam releases intended to rebuild sand bars. The contrasting patterns of channel adjustment in these rivers indicate that the opportunities and cost of restoration are likely to differ in relation to the sediment supply available for channel restoration.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1808 Dams
DE: 1821 Floods
DE: 4863 Sedimentation (1861)
DE: 6334 Regional planning (1880)
SC: Hydrology [H]
MN: 2007 Fall Meeting