Submitted to: Government Publication/Report
Publication Type: Proceedings
Publication Acceptance Date: 3/3/2004
Publication Date: 10/18/2004
Citation: Kuhnle, R.A., Wren, D. 2004. Simultaneous side by side variability of sediment concentration over dunes. Proceedings of the Ninth International Symposium on River Sedimentation, Yichang, China, pp. 2556-2562. Publication/Report. Interpretive Summary: Knowledge of the rate of sediment being moved in the water column of stream channels is necessary for several reasons: the sediment may fill reservoirs and reduce their capacity, may fill channels and cause flooding, may degrade water quality, and may cause instability of the channel banks which can cause the destruction of valuable agricultural and other lands. The collection of accurate samples of sand in a stream channel requires information about the variability of sediment movement across the channel. Currently there is very little information available about the variability of sediment movement across a stream channel. A series of experiments were conducted in a model stream channel in the laboratory to measure and characterize the changes in the amount of sediment in the water column across the channel. Two samples collected at the same time across the channel were found to vary by as much as 40%. This study has led to a more complete understanding of the variation of sand movement across a sand-bottom stream or river channel. The information from this study is critical for improving sediment prediction and sampling techniques and will lead to advances which will allow agricultural and other watersheds to be managed in a more informed and environmentally sensitive manner.
Technical Abstract: A series of laboratory experiments were conducted in a laboratory flume to characterize the lateral variations of suspended sediment over dunes. Forty experimental runs were made using flow depths of 0.33 and 0.13 m in a 1.2 m wide flume channel. The Froude number was 0.5 and the median diameter of the bed material was 0.52 mm. Point samples and depth-integrated values calculated using acoustic backscatter data of suspended sediment were collected simultaneously at two lateral positions at spacings of 0.40, 0.20, 0.10 and 0.05 m. Mean absolute differences between the paired point samples were shown to increase and then level off to values of about 40 percent of the mean concentration as the lateral spacing between samples was increased. Mean absolute differences for paired depth-integrated samples had a similar pattern with values of 30% for the largest spacing. The information provided by this study has important implications for the testing of emerging techniques for measuring suspended sediment in fluvial environments.