|Hjelmfelt Jr, Allen|
Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Abstract Only
Publication Acceptance Date: 7/11/2000
Publication Date: N/A
Technical Abstract: The performance of the BASINS/NPSM model (version 2.01) in simulating hydrology from a 7,250-ha watershed with a claypan soil was evaluated. Using BASINS default input parameters, the model overpredicted mean annual stream flow by 52%; groundwater flow contributed 84% of the total stream flow, which is extremely high from watersheds in the claypan soil region. Overprediction of the model was a result of several stream flow events tha the model simulated mainly from groundwater flow whereas no stream flow was measured. For the stream flow events where measured flow was >2 mm, the model under-predicted annual stream flow by 57%. To improve the prediction of the model, key hydrologic parameters that influence surface and groundwater flows were calibrated in this study. The model was found to be sensitive to INFILT (infiltration rate), AGWRC (basic groundwater recession rate), LZSN (lower zone nominal storage), UZSN (upper zone nominal storage), and DEEPFR (fraction of groundwater inflow which enters deep) parameters. When calibrated, the predicted mean annual stream flow was 19% higher than that measured, and surface flow contributed 65% of the total flow. The model performed extremely well for the events where measured runoff was >2 mm. The difference between measured and predicted mean annual stream flow for these events was <3%. Although BASINS provides useful estimates for many NPSM input parameters, this study showed that for hydrologic simulation of watersheds in a claypan soil, some of BASINS default input parameters need to be calibrated. In the future, BASINS/NPSM will be calibrated for herbicide, nitrates, and sediment simulations so that the model can be used in the development of TMDLs for other claypan soil watersheds.