Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2003
Publication Date: 8/1/2005
Citation: Wren, D.G., Bennett, S.J., Barkdoll, B.D., Kuhnle, R.A. Variability in suspended-sediment concentration over mobile, sand beds. Journal of Hydraulic Engineering. 131(8): 733-736. Interpretive Summary: The amount of suspended solids transported in rivers and streams is an important parameter in understanding watershed processes and for managing the environment. Changes in land-use, climate, and stream channel shape and size may increase or decrease the amount of sediment that is eroded and transported through a river. Understanding these relationships is particularly important in the development of criteria for determining the maximum amount of clean sediment that can pass through a river without causing any adverse effects on aquatic wildlife. Much depends on the effectiveness of sediment sampling programs, the accuracy of the measurements, and the physical interpretation of the results. A study was undertaken to examine the variability of suspended sediment concentration in a laboratory channel. Using a channel filled with sand and flow conditions where suspended sediment concentrations were high, repeated measurements of sediment concentration were made. It was shown that suspended sediment concentration varied greatly both in time and in the location of the sampler. In general, very long sample times were required to obtain accurate and reliable measurements of the mean suspended sediment concentration. The magnitudes and sources of variability discussed here have important implications for federally sponsored sampling programs for suspended solids and the accuracy and reliability of the results.
Technical Abstract: Suspended-sediment flux measurements are used to determine, among other things, Total Maximum Daily Loads (TMDL), the effects of hydraulic structures on sediment transport, and watershed stability. The accuracy of suspended-sediment sampling programs and how they are affected by different bed and flow conditions are of interest to agencies and individuals who make decisions based on suspended-sediment flux data. Variability in suspended-sediment concentration for a stationary observer, moving observer, and for laterally separate samples was examined for dune and upper-stage plane bed conditions. A much greater sampling time was required to reliably predict mean concentration in dune than upper-stage plane bed conditions. Laterally separated, simultaneous samples in both dune and upper-stage plane beds were poorly correlated. It was also found that for dunes, the region above point of flow re- attachment on the stoss side of a dune was found to have higher suspended-sediment concentrations further from the bed than at other locations relative to dune length. The magnitudes and sources of variability discussed here have implications for suspended-sediment sampling programs.