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WATER RESOURCES RESEARCH, VOL. 42, W11411, doi:10.1029/2005WR004847, 2006

Debris flow deposition and reworking by the Colorado River in Grand Canyon, Arizona

Brian J. Yanites

Department of Geological Sciences, University of Colorado, Boulder, Colorado, USA


Robert H. Webb

U.S. Geological Survey, Tucson, Arizona, USA


Peter G. Griffiths

U.S. Geological Survey, Tucson, Arizona, USA


Christopher S. Magirl

U.S. Geological Survey, Tucson, Arizona, USA


Abstract

Flow regulation by large dams affects downstream flow competence and channel maintenance. Debris flows from 740 tributaries in Grand Canyon, Arizona, transport coarse-grained sediment onto debris fans adjacent to the Colorado River. These debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream. Beginning in 1963, flood control operations of Glen Canyon Dam limited the potential for reworking of aggraded debris fans. We analyzed change in debris fans at the mouths of 75-Mile and Monument Creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005. Our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003. Volume, area, and river constriction increased at both debris fans. Profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases, and surface shape shifted from concave to convex. Dam releases above power plant capacity partially reworked both debris fans, although reworking removed much less sediment than what was added by debris flow deposition. Large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in Grand Canyon.

Received 30 December 2005; accepted 26 July 2006; published 18 November 2006.

Keywords: debris flows; regulated rivers; geomorphology; Grand Canyon; Colorado River.

Index Terms: 1824 Hydrology: Geomorphology: general (1625); 1810 Hydrology: Debris flow and landslides; 1808 Hydrology: Dams; 1895 Hydrology: Instruments and techniques: monitoring.

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Citation: Yanites, B. J., R. H. Webb, P. G. Griffiths, and C. S. Magirl (2006), Debris flow deposition and reworking by the Colorado River in Grand Canyon, Arizona, Water Resour. Res., 42, W11411, doi:10.1029/2005WR004847.