SEDHYD-2023, Sedimentation and Hydrologic Modeling Conference

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Continuous Measurement of Bed Load On Goodwin Creek Using Impact Plates

Measurements or predictions which accurately represent the rate of bed load transport by gravel-bed channels are difficult to make. Yet, accurate estimates of the rate of bed load transport are necessary for assessing and designing stable channels in agricultural and other watersheds. To improve our knowledge of the rate of gravel bed load transport within the channels of the Goodwin Creek Experimental Watershed, Mississippi, USA, two impact plates (0.35 x 0.50 x 0.016 m) were installed near the center of the channel at the upstream end of a supercritical flow measurement structure. The channel at the study site drains 17.9 square kilometers of the 21.3 square kilometer watershed. The bed material ranges in size from 0.06 to 90 mm with a median size of 8.3 mm. Flows in the channel of sufficient strength to entrain the gravel fractions of the bed material occur during rainfall events most commonly during the winter and spring months of the year. The flow in the channels is highly flashy with the channel going from low base flow to sediment transporting flows in periods of tens of minutes. Since December of 2021, when the impact plates first became operational, continuous gravel bed load data has been collected from more than 20 runoff events in their entirety. Physical samples of transported gravel bed load have been collected during the 25 May, 2022 runoff event. Preliminary calibration relations have been developed between the mass of the impacting grains and the peak amplitude and frequency of the recording impacts. Generally, the flow strength at initiation of motion of the gravel during the rising limb of the hydrograph was greater than the flow strength at cessation of motion during the falling limb, and the flow magnitude of the initiation of motion was related to the elapsed time and peak flow of the most recent antecedent flow. Bed load rates and grain sizes have been observed to fluctuate over several orders of magnitude for similar flows. These observations are preliminary and data collection and analyses are ongoing.

Roger Kuhnle
National Sedimentation Laboratory, USDA-ARS
United States

James Smith
Department of Geography, Simon Fraser University
Canada

Daniel Wren
National Sedimentation Laboratory, USDA-ARS
United States

 



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