HR: 1340h
AN: H43C-0511    [Abstracts]
TI: Remote Sensing of Debris Flow Deposition and Reworking by the Colorado River in Grand Canyon, Arizona
AU: * Yanites, B J
EM: Brian.Yanites@colorado.edu
AF: Department of Geological Sciences, University of Colorado, Campus Box 399 2200 Colorado Ave., Boulder, CO 80309 United States
AU: Webb, R H
EM: rhwebb@usgs.gov
AF: U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ 85719 United States
AU: Griffiths, P G
EM: pggriffi@usgs.gov
AF: U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ 85719 United States
AU: Magirl, C S
EM: magirl@usgs.gov
AF: U.S. Geological Survey, 520 N. Park Avenue, Tucson, AZ 85719 United States
AB: Debris flows from 740 tributaries transport sediment ranging from clay to large (>3m) boulders into the Colorado River in Grand Canyon, Arizona. The resulting debris fans constrict the river to form rapids. Debris fans and rapids are in turn altered by the river, which entrains particles and transports them downstream. River regulation in Grand Canyon began with the closure of Glen Canyon Dam in 1963, and the geomorphic character of the debris fans has been adjusting to the change in flow regime ever since. Previous studies have suggested that the debris fans have and will continue to aggrade in response to reduced discharge on the Colorado River. In order to monitor and evaluate changes in debris fans, we created a time series of digital terrain models for two frequently aggraded debris fans (75-Mile Wash and Monument Creek) using ground surveys and photogrammetry acquired between 1984 and 2005. Two-dimensional photogrammetric analysis was extended to include years 1965 and 1973. Debris fan volume, surface area, and river constriction confirm that these two debris fans have recently aggraded owing to multiple debris flows that occurred from 1984 through 2003. Debris fan volumes increased at 75-Mile Wash by over 10,000 m³ and at Monument Creek by almost 8000 m³. Some of this aggradation is likely the effect of the preferential growth of small, non-resolvable plants and settling of sediments in topographical lows. Aggradation has also altered the geometry of the fans. Profiles of the surface models show maximum aggradation near the middle of the debris fan and a shift of surface morphology from a concave to a convex profile. Although small controlled-flood releases partially reworked both fans at the edges, reworking removed far less sediment than was added by debris-flow deposition. This is partly the result of the geography of debris-flow deposition, as material deposited in the middle of the fan can be reworked only by large floods that overtop the debris fans. Our results indicate that photogrammetry, if carefully analyzed for surface-model quality, can be an effective tool for monitoring and quantifying the intertwined effects of debris-flow deposition and mainstem discharge on canyon river morphology.
DE: 1808 Dams
DE: 1810 Debris flow and landslides
DE: 1824 Geomorphology: general (1625)
DE: 1855 Remote sensing (1640)
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005