MODELING THE PARTICLE SIZE DISTRIBUTION OF ERODED SEDIMENTS DURING SHALLOW OVERLAND FLOW

Recent advances in watershed and sediment transport modeling have made possible the evaluation of the component processes controlling sediment transport from upland or overland flow areas. Many watershed models now exist which estimate total watershed sediment yield. Some of the models, such as the distributed parameter models, are quite adaptable and can describe both spatially and temporally the response of watersheds to different sediment control strategies. The vase majority of the models are, however, stochastic or lumped parameter models and have great difficulty describing the response of watersheds to local, site specific management practices. This research involved incorporating a new sediment transport model based on Yalin\u27s work into the ANSWERS distributed parameter watershed model. The new model can describe the transport of individual particle size classes in a sediment mixture during the overland flow process. The sediment transport model was verified using particle size distribution data collected from rainulator plot studies conducted by the USDA. The plots consisted of three identical 1.8 m wide by 10.7 m concave slope test strips with slopes varying from 18 percent at the top to zero percent at the bottom. The plots were subjected to uniform simulated rainfall and the particle size distributions of the transported sediment were measured at a different downslope location on each test strip. The model was verified by simulating the test plots and comparing the output with the observed particle size distributions at different points on the slopes. The results of the verification runs were quite satisfactory. Additional verification runs for gross sediment yield were conducted on the 714 hectare Upper Black Creek watershed. The results were also satisfactory. The model was then used to simulate the effects of different sediment control practices on a construction site in central Indiana to evaluate its ability to provide land use and management practice information. The results were the basis of several specific management recommendations