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Flume experiments in support of multi-beam bed load measurement in rivers
Proceedings of the 2020 Mississippi Water Resources Conference
Year: 2020 Authors: Wren D., Kuhnle R.A., McAlpin T., Jones K., Abraham D.
Measuring sediment transport in large rivers is problematic, due to high water depth and large bed forms that make it difficult to obtain accurate physical samples near the bed of the river, where most sediment is transported. Additionally, sediment transport is highly variable in space, which means that multiple physical samples must be collected to reach a reasonable estimate of load for a river cross-section. Another problem that compounds error is that bed forms are not consistent over a cross-section, which means that samples from a given cross-section will likely be collected over different parts of bed forms that will yield a wide range of sediment concentrations. In order to overcome these issues, repeated multi-beam acoustic surveys of bed topography can be used to arrive at reach-averaged sediment transport rates. This technique is relatively rapid, does not require physical samples, and accounts for the spatial variability inherent in sand transport. An established methodology for converting repeated bed topography measurements to sediment load is ISSDOTv2, which stands for Integrated Section, Surface Difference Over Time; however, there is a need for establishing error bounds and further developing the methodology. Since it is nearly impossible to collect enough physical samples to validate the method in a river, flume experiments at the National Sedimentation Laboratory were initiated to estimate error bounds for the ISSDOTv2 method, to continue development of the method, and to evaluate its performance in unsteady and spatially variable sediment transport scenarios. Results from the flume experiments, including independent measurements of bed load, suspended load, and bed topography will be presented.