|Ascough Ii, James|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/1997
Publication Date: N/A
Citation: N/A Interpretive Summary: The USDA-Water Erosion Prediction Project (WEPP) model was developed to estimate runoff and sediment yield for small agricultural watersheds located throughout the United States. WEPP user requirements dictate that the impoundment component must simulate the sedimentologic response of several types of impoundments including farm ponds, terraces, culverts, filter fences, and check dams. Algorithms and computer code for the sedimentation simulation portion of the WEPP Surface Impoundment Element (WEPPSIE) were developed and validated for a variety of possible impound- ment geometries and outflow structures. The sedimentation algorithms are based upon an analogy to the overflow rate and conservation of mass. Two parameters were developed and included in the determination of sediment deposition. These parameters are empirical factors used to account for the effects of impoundment geometry, hydraulic response, and stratification of the suspended sediment. WEPPSIE sediment routing result showed excellent agreement when compared against results obtained with the more complex CSTRS model. The WEPPSIE sedimentation algorithms were also validated against experimental impoundment data. Taken as a whole, WEPPSIE satisfied the impoundment user requirements of the WEPP model by producing in the WEPPSIE predicted versus observed trapping efficiency averaged 5/5% reasonable predictions of effluent sedimentation concentration for impoundments covering a wide range of geometries and outflow structures.
Technical Abstract: The sedimentation algorithms included in the Water Erosion Prediction Project Surface Impoundment Element (WEPPSIE) are described and validated in this paper. Algorithms and computer code were developed to perform hydraulic routing and determine sedimentation and deposition in impoundments with a wide variety of geometries and outflow structures including drop spillways, perforated risers, culverts, open channels, emergency spillways, rock fill check dams, filter fence, and straw bales. Sedimentation is determined using conservation of mass along with continuous stirred reactor and overflow rate concepts to account for the effects of impoundment geometry, hydraulic response, and stratification. Using a data set that was optimized against results from the more complex CSTRS model, prediction models for the calibration coefficients were developed based upon easily computed hydraulic and geometric paramenters. The sedimentation procedures were validated against an independent data se created with the CSTRS model and the average difference in trapping efficiency was 2.6%. The sedimentation procedures were also validated against data developed in a pilot scale impoundment with an average difference in trapping efficiency of 5.5%. Taken as a whole, WEPPSIE satisfied the impoundment user requirements of the WEPP model by producing reasonable predictions of effluent sedimentation concentration for impoundments covering a wide range of geometries and outflow structures.