The completion of Glen Canyon Dam in 1963 altered the transport of sediment in the Colorado River through Grand Canyon National Park. By the mid-1970's, river runners and scientists had noticed that some of the sandy beaches were disappearing and the plant and animal life along the river was changing. It was theorized that controlled floods could be used to transfer sand from the channel bed to eddies, increasing both the area and volume of eddy sandbars. However, results from the controlled experimental flood carried out in 1996 and from subsequent studies indicate that sand deposited at higher elevations in eddy sandbars is derived mostly from the lower parts of these bars rather than from the bed, resulting in bars that are smaller in area and volume. Sand transport in the river is now approximately equally regulated by changes in the discharge of water and changes in the grain sizes of sand on the channel bed and eddy sandbars, with suspended-sand transport regulated more by changes in the surface grain size of eddy sandbars than by changes in the grain size of sand on the bed of the channel.
The closure of Glen Canyon Dam also appears to have increased the frequency of debris flows in the Grand Canyon, with debris flows occurring, on average, five times per year. Depositing sediment ranging in size from clay to boulders, debris flows raise the river bed at tributary junctions until floods rework the debris deposits and reposition boulders. Potentially hazardous to the recreational community, debris flows are natural phenomena that appear unaffected by current land-use practices in the tributary drainages within the Grand Canyon.
Topping, D.J., Rubin, D.M., and Schmidt, J.C., 2005, Regulation of sand transport in the Colorado River by changes in the surface grain size of eddy sandbars over multi-timescales: Sedimentology, v. 52, Issue 5, Page 1133-1153.
Hereford, R., 2003, Map showing Quaternary geology and geomorphology of the Lonely Dell Reach of the Paria River, Lees Ferry, Arizona, with comparative landscape photographs. U.S. Geological Survey Geologic Investigations Series Map I-2771 - with accompanying pamphlet:
Webb, R.H., and Hereford, R., 2003, Comparative landscape photographs of the Lonely Dell area and the mouth of the Paria River.
Magirl, C.S., Webb, R.H., and Griffiths, P.G., 2005, Changes in the water surface profile of the Colorado River in Grand Canyon, Arizona, between 1923 and 2000: Water Resources Research, v. 41, W05021, doi:10.1029/2003WR002519
Griffiths, P.G., and Webb, R.H., 2004, Frequency of initiation of debris flows in Grand Canyon, Arizona: Journal of Geophysical Research, v. 109, F04002, doi:10.1029/2003JF000077, 2004.
Webb, R.H., Griffiths, P.G., Magirl, C.S., and Hanks, T.C., 2005, Debris flows in Grand Canyon and the rapids of the Colorado River, in Gloss, S.P., Lovich, J.E., and Melis, T.S., eds., The State of the Colorado River Ecosystem in Grand Canyon: U.S. Geological Survey Circular 1282, p. 119-132. (pdf format
Wright, S.A., Melis, T.S., Topping, D.J., and Rubin, D.M., 2005, Influence of Glen Canyon Dam operations on downstream sand resources of the Colorado River in the Grand Canyon, in Gloss, S.P., Lovich, J.E., and Melis, T.S., eds., The state of the Colorado River ecosystem in Grand Canyon: U.S. Geological Survey Circular 1282, p.17-31. (pdf format)
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For additional information, including additional references, see the projects, Environmental Fluid Dynamics or Response of Fluvial Systems to Climatic Change, or contact David J. Topping, firstname.lastname@example.org or Robert H. Webb, email@example.com )