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United States Department of Agriculture

Agricultural Research Service

Title: The Effect of Spatial and Temporal Separation on Suspended-Sediment Concentration Measurements

Authors
item Wren, Daniel - UNIVERSITY OF MISSISSIPPI
item Bennett, Sean
item Barkdoll, Brian - UNIVERSITY OF MISSISSIPPI
item Kuhnle, Roger

Submitted to: International Conference on Hydroinformatics
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2000
Publication Date: N/A

Interpretive Summary: The amount of suspended solid material in rivers and streams often is used as the primary indicator for watershed integrity and the success or failure of engineering measures and best management practices implemented upstream. Hence, much depends on the effectiveness of sediment sampling programs, how representative are the measurements, and the physical interpretation of the results. It is well known that sediment samples must average over the passage of several bed waves to adequately represent the average concentration of suspended solids at a point. Less attention has been given to the degree of error introduced by sampling in a limited number of locations across a stream. Experiments were carried out to determine the minimum and maximum variability likely to occur due to sampling at different locations in a cross-section and at a point. Variability in suspended-sediment concentration from the viewpoints of a stationary observer, moving observer, and from samples separated in space was examined for two different riverbed conditions. The sampling time necessary to obtain the average suspended-sediment concentration for the higher-velocity flow was determined to be about 30 seconds while for the lower-velocity flow it was found to be about 1.2 hours. The degrees and sources of variability discussed here have important implications for federally regulated sampling programs for suspended solids, the assessment of the accuracy of results, and the reliability of the measurements.

Technical Abstract: The spatial and temporal scales of suspended-sediment sampling have a profound effect on the quality of concentration data and the interpretation of results. It is well known that samples must average over the longitudinal passage of several bed forms to adequately represent the average suspended-sediment concentration at a point. Less attention has been given to the degree of error introduced by sampling in a limited number of locations in a stream cross-section. Experiments were carried out to determine the minimum and maximum variability likely to occur due to sampling at different locations in a cross-section and at a point. Variability in suspended-sediment concentration from the viewpoints of a stationary observer, moving observer, and from laterally separate samples was examined for both dune and upper-stage plane bed conditions. The sampling time necessary to obtain the average suspended-sediment concentration for the upper-stage plane bed was determined to be about 30 seconds while for the dune-covered bed it was found to be about 1.2 hours. The degrees and sources of variability discussed here have implications for suspended-sediment sampling programs and the assessment of their accuracy.

Last Modified: 10/26/2014
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