Submitted to: American Society of Civil Engineers Water Resources Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/21/2001
Publication Date: N/A
Interpretive Summary: Accurate determinations of the rate of sediment being moved on the bottom of stream channels are necessary because 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 information on the erosion and movement of sediment by streams provided by accurate instruments and techniques is critially needed by land use managers to allow them to make informed decisions on the best way to manage agricultural and other watersheds for sustainable production in an environmentally sensitive manner. To reduce costs and allow more and higher quality sediment samples to be collected, automatic samplers using new technologies such as acoustics are needed. This paper reports the results from a study in which a set of sediment samples was collected using g2 identical samplers at the same time and flow depth at points one third and two thirds way across a laboratory stream channel. The information from these paired sediment samples documents the degree of variability to be expected from two identical samplers are used at the same time. This information is critically needed for the testing of new samplers such as those that employ acoustics.
Technical Abstract: The establishment of Total Maximum Daily Loads (TMDL) for contaminants entering water bodies requires the development of sitable methods for contaminant measurement. In an effort to assess quantities of suspended-sediment transport, an acoustic device is being developed in a collaborative effort between the University of Mississippi's National Center for Physical Acoustics and the Department of Civil Engineering along with the USDA-ARS National Sedimentation Laboratory with support from the National Science Foundation. The acoustic device will be non- intrusive, automatic, and provide suspended-sediment concentration and particle-size information at many points throughout the flow depth in a short time period. In order to test the new acoustic device, validation against an established measurement method is necessary. Due to the properties of the acoustic technique, this validation cannot be performed by sampling directly beneath the device. Towards this end, a laboratory flume with a sediment-starved bed was used to establish whether laterally separated samples collected simultaneously at like elevations within the flow would have similar concentrations. It was found that the average error, after a constant correction was applied, was 6%. This was deemed acceptable for use in instrument testing. Starved bed results are compared with previously collected data in dune and upper-stage plane bed regimes, demonstrating the profound effect of a mobile bed on the accuracy of suspended-sediment sampling.