Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 1/8/2001
Publication Date: N/A
Interpretive Summary: The amount of suspended solid material transported in rivers and streams often is used as the primary indicator for watershed integrity, the success or failure of engineering measures and best management practices implemented upstream, and a direct measure of water quality. Hence, much depends on the effectiveness of sediment sampling programs employed, how representative are the measurements, and the physical interpretation of the results. This report summarizes three years of research examining the transport of suspended sediment in an experimental channel. It was shown that (1) acoustic techniques for measuring suspended sediment are the most in need of further use and development, (2) the variability of sediment concentration measured simultaneously at two locations within the flume show little correlation to each other and are highly variable in time and space, (3) a new method for calculating the lateral mixing of suspended sediment using velocity data is comparable to those previously reported, and (4) the distribution of flow velocity and suspended sediment concentration within the experiments agree well with general theory with only slight modification. The results presented here will aid federal agencies in their measurement, interpretation, and assessment of total sediment load in streams and rivers.
Technical Abstract: The measurement and variability of suspended-sediment concentrations are important areas in river hydraulics. In this report, methods for measuring suspended-sediment concentration are reviewed in detail, resulting in the conclusion that acoustic techniques are the most in need of further use and development. The variability of time series of suspended-sediment concentration data taken at a single point and taken simultaneously at two laterally separated positions in both dune and upper-stage plane beds is examined. Concentration was found to vary greatly in both conditions, with no correlation between simultaneous samples. A new method for calculating the transverse diffusion coefficient using turbulent velocity fluctuations and transverse velocity gradients in a sediment-laden flow is described, with results comparable to those measured in natural rivers and in previous flume studies. Velocity profiles, turbulence intensities, and suspended-sediment concentrations obtained in super-critical conditions in a sediment-laden flow were compared to theory. Velocity profiles showed good agreement with the law of the wall, the magnitude of turbulence intensities was found to depend on the measurement technique, and the Rouse equation was modified to better-fit concentration profiles over flat, mobile beds.