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United States Department of Agriculture

Agricultural Research Service

Title: Coupling Sediment Transport with the Dryland Environment 1665

Authors
item Yuill, B. - ARIZONA STATE UNIVERSITY
item Nichols, Mary
item Shipek, David
item Schmeeckle, M. - ARIZONA STATE UNIVERSITY

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 18, 2004
Publication Date: December 16, 2004
Citation: Yuill, B.T., Nichols, M.H., Shipek, D.C., Schmeeckle, M. 2004. Coupling sediment transport with the dryland environment. [Abstract]. EOS Trans. AGU, 85(47), Fall Meet. Suppl., Abstract 4653.

Interpretive Summary: The hydrologic response of dryland fluvial systems is unique in comparison with that of humid fluvial systems. Infrequent, high intensity precipitation events produce the effective flow discharge, controlling channel morphology. Transport efficiency in dryland ephemeral channels is often orders of magnitude higher than similar in perennial streams with bedload transport making a relative higher contribution to overall sediment yield, which is fully transport capacity limited. Because of the infrequency of the transport events in dryland fluvial systems, empirically based datasets are rare. Acceptable predictions of sediment transport rates and yields based on available simulations models span a broad range of values. High quality field data are critical to improving simulation models. A research project was initiated in 2004 to measure and model sediment transport processed in low-order dryland channels based on detailed field data collection. The USDA ARS has monitored the Walnut Gulch Experimental Watershed near Tombstone, Arizona for over 50 years. The area is semiarid rangeland, receiving an average of 350 mm of precipitation annually. The Lucky Hills watershed, an 11.4 acre sub-watershed, is intensively monitored for precipitation and run-off. Two traversing slot-samplers and pit traps have been installed to measure sediment transport within its main channel. Historical local research and a decade of comprehensive cross-section surveys provide information on channel morphology change. Historic runoff and sediment data are analyzed to define relationships between the two. Findings are coupled with recent field surveys of channel morphology, bed substrate, affecting vegetation, and evidence of hillslope processes to provide a greater understanding of regional landscape evolution. Even in a small, relatively uniform watershed like Lucky Hills, controlling processes are highly complex and vary dramatically in time and space. The wealth of historical data available at Walnut Gulch is a rare and valuable asset helping to overcome these inherent difficulties with the study of dryland fluvial geomorphology.

Technical Abstract: The hydrologic response of dryland fluvial systems is unique in comparison with that of humid fluvial systems. Infrequent, high intensity precipitation events produce the effective flow discharge, controlling channel morphology. Transport efficiency in dryland ephemeral channels is often orders of magnitude higher than similar in perennial streams with bedload transport making a relative higher contribution to overall sediment yield, which is fully transport capacity limited. Because of the infrequency of the transport events in dryland fluvial systems, empirically based datasets are rare. Acceptable predictions of sediment transport rates and yields based on available simulations models span a broad range of values. High quality field data are critical to improving simulation models. A research project was initiated in 2004 to measure and model sediment transport processed in low-order dryland channels based on detailed field data collection. The USDA ARS has monitored the Walnut Gulch Experimental Watershed near Tombstone, Arizona for over 50 years. The area is semiarid rangeland, receiving an average of 350 mm of precipitation annually. The Lucky Hills watershed, an 11.4 acre sub-watershed, is intensively monitored for precipitation and run-off. Two traversing slot-samplers and pit traps have been installed to measure sediment transport within its main channel. Historical local research and a decade of comprehensive cross-section surveys provide information on channel morphology change. Historic runoff and sediment data are analyzed to define relationships between the two. Findings are coupled with recent field surveys of channel morphology, bed substrate, affecting vegetation, and evidence of hillslope processes to provide a greater understanding of regional landscape evolution. Even in a small, relatively uniform watershed like Lucky Hills, controlling processes are highly complex and vary dramatically in time and space. The wealth of historical data available at Walnut Gulch is a rare and valuable asset helping to overcome these inherent difficulties with the study of dryland fluvial geomorphology.

Last Modified: 7/30/2014
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