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CHARACTERISTICS OF TRANSPORTED SEDIMENT FROM SMALL SEMIARID WATERSHEDS DURING THUNDERSTORM GENERATED RUNOFF

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Pp. 130-135tmdl in Total Maximum Daily Load (TMDL) Environmental Regulations–II Proceedings of the 8-12 November 2003 Conference (Albuquerque, New Mexico USA), Publication Date 8 November 2003.  .(doi:10.13031/2013.15548)
Authors:   M. H. Nichols
Keywords:   Bedload, Sediment Transport, Semiarid, Ephemeral Channel

Vast areas of rangeland in the semiarid southwestern US are characterized by ephemeral channels that transport sediment during occasional flows. Reducing the amount of sediment in surface water runoff can improve water quality and minimize the impact of upland activities on downstream water users. Because measuring transported sediment in natural channels during highly variable flow conditions is difficult and expensive, total load measurements are relatively rare. There is a need for data, and subsequent interpretation, describing the characteristics of sediment transported in suspension and as bedload in semiarid rangeland regions, for improving prediction technologies and assessing regulatory compliance. Runoff and sediment data are collected at the outlet of a 4.53 ha upland watershed on the USDA-ARS Walnut Gulch Experimental Watershed in southeastern Arizona. A critical depth runoff-measuring flume and depth-integrated traversing slot sampler collects runoff and sediment during flow events. Although the traversing slot collects a depth-integrated sample, computed concentration values do not represent sediment particles greater than the 13 mm slot width. During the 2002 runoff season, a tank was installed at the outfall of the flume to trap coarse sediment. Total load was characterized by coupling sampled sediment < 4 mm collected with the traversing slot and sediment > 4 mm trapped in the tank for three runoff events. Sediment particles larger than 4 mm make up as much as 15% of the total sediment load transported during the measured events.

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