Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2006
Publication Date: 8/28/2006
Citation: Cochrane, T.A., Flanagan, D.C. 2006. Sediment deposition in a simulated rill under shallow flow conditions. Transactions of the ASABE. 49(4):893-903.
Interpretive Summary: This paper presents results of a series of laboratory experiments that were conducted in a flume that simulates a rill channel out in an agricultural field. Sediment particles (sand, tiny glass beads, or large plastic/glass beads) were supplied to the bed from both the top and from the sides at different rates. Also, the rainfall falling on the water flow in the rill as well as the infiltration rate could be controlled. A special laser instrument was used to very accurately measure the depth of sediment that was either removed from the flume bed or deposited on the flume bed from the flowing water. Sediment particles that were less dense (glass beads and large plastic/glass beads) were affected more by the rainfall rates and depth of the water flow than the more dense sand particles. Some erosion prediction equations were tested with the data collected here, and they worked okay for the sand particles and large plastic/glass beads, but not very well for the small glass beads. Values were calculated for a turbulence factor in one of the erosion equations using this data, and may improve estimates of sediment deposition in erosion models. This work will impact other scientists and users of erosion prediction models, because it shows how these models might be able to be improved. Erosion prediction technology is used within the United States to assess the impacts of various land management practices on potential soil erosion and sediment losses from agricultural and other land uses.
Technical Abstract: Experiments to study the processes of erosion mechanics are fundamental to the understanding of erosion and subsequently for our ability to accurately predict erosion with process-based models such as WEPP. An experimental laboratory hydraulic flume apparatus under rainfall simulators was used to study sediment deposition in a 25 cm wide rill as influenced by water flow rate, rainfall intensity, infiltration, and sediment type. Sediment feeders were used to add sediment and water to the top of a simulated rill as well as to the sides of the rill to simulate contributions of interrill erosion to the rill as would occur in natural conditions. A laser scanner was used to quantify the amount of deposition that occurred after each experiment and sediment concentration samples were taken from the flume outlet to quantify sediment transport in the rill during the run. The experiments were conducted using silica sand, glass beads, and artificial plastic/glass aggregates with average diameters of 330 µm, 150 µm, and 3 mm and specific gravities of 2.65, 2.5, and 1.25 respectively representing a variety of soil conditions. Combinations of different flow rates, rainfall intensities, and sediment feed rates were studied for each sediment type at low slopes. The objective of these experiments was to determine if shallow water flow as influenced by rainfall intensity, infiltration rate, and incoming sediment concentration had a significant effect on the deposition of sediment in a rill. Results showed that the interaction of rainfall intensity and flow depths had a more significant effect on deposition of particles of low specific gravity and under higher interrill sediment contributions; however this was not obvious for denser particles such as sands. The effect of infiltration on sediment deposition was observed to be related to the slope steepness. It was also shown that under no rainfall and high intensity rainfall sediment deposition in the rill was less than deposition under medium intensity rainfall. Results from the sediment output showed that the estimation of sediment transport using the equation in WEPP for sands and artificial plastic/glass aggregates was acceptable, but not acceptable for glass beads. Modeling efforts showed that the current WEPP equation may be improved by incorporating a turbulence factor based on rainfall intensity and flow depth.