|Hjelmfelt Jr, Allen|
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2001
Publication Date: N/A
Interpretive Summary: States are required by the Environmental Protection Agency to develop Total Maximum Daily Load (TMDL) standards for rivers in their state. These TMDLs are used to establish the ability of the river to assimilate contaminants. Thus, runoff into the river can be controlled to limit degradation of the water resource. The recommended procedure requires application of the computer model, Hydrologic Simulation Program-Fortran (HSPF). The validit of the model for erosion studies in many agricultural regions is not known. Also, data with parameter recommendations and model sensitivity to those parameters are not always available. The intensive data sets collected by the Missouri Management Systems Evaluation Area (MSEA) and Agricultural Systems for Environmental Quality (ASEQ) projects provide an excellent opportunity for evaluating the HSPF model. Our results showed that the model could be used to obtain reasonable estimates of sediment yield. We were, however, unable to correctly simulate soil loss from large rainfall events. We also found it difficult to adjust the model to account for changes due to tillage operations. This study provides additional model parameter values plus details of the parameter development. The results will assist hydrologists and water quality modelers in establishing reasonable TMDLs for sediment in streams and rivers.
Technical Abstract: The performance of Hydrological Simulation Program-FORTRAN (HSPF) version 11.0 in simulating sediment yield from a claypan agricultural watershed was evaluated. The calibration of model parameters required to describe sediment behavior constituted the major research. The claypan watershed studied is Goodwater Creek, a 73 km**2 agricultural watershed in Central Missouri, which is characterized by a level to gently rolling topography, with slopes averaging 3%. In this study, the HSPF model was first calibrated for land surface sediment erosion on a 36-ha research field within the Goodwater Creek watershed. Calibration for instream sediment transport was done for the entire Goodwater Creek watershed. Modeling the impacts of field activities, such as cultivation, on soil erosion in HSPF was through resetting the variable DETS, the detached sediment storage on the land surface. Our results showed that as the size of the watershed area increased, the gains of resetting DETS diminished significantly. Thi is an important finding because of the difficulty in estimating correct DETS reset values. We also found that HSPF tended to overpredict sediment yield from a claypan soil for large rainfall events. In general, however, it is concluded that HSPF can successfully simulate sediment yield from the Goodwater Creek, a claypan soil watershed.