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Title:   Author  item
                                            Feyereisen, Garyitem
                                            Strickland, Timothy

                                                         - *Tim*item
                                            Bosch, David

                                                         - *Dave*item
                                            Batten, Herman
  Submitted to: Proceedings of American Society of Agricultural Engineers
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 7/29/2005
                                    Publication  Date: 7/29/2005
                                    Citation: Feyereisen, G.W., Strickland, T.C., Bosch, D.D., Batten, H.L. 2005. Evaluation of swat input parameter undertainty for the little river watershed. In: Proceedings of American Society of Agricultural Engineers. ASAE Paper No. 052167.Interpretive Summary: The loss of sediment, nutrients, and pesticides into surface waters of the Southeast Coastal Plain is being monitored within the Little River Experimental Watershed, an area of about 130 square miles just northwest of Tifton, Georgia.  There is a need to know how various agronomic and conservation practices, and climate affect the water quality in the region.  In order to extend analysis to longer time frames, computer simulation models are utilized to mimic the response of the natural landscape.  Questions such as:  “What if 50% of the cropped land were in conservation tillage?” or “What if 100% of the cropped land were in conservation tillage?” or “What if 25% of the cropped land was converted to permanent plantings?” can be analyzed.  Computer simulations do not perfectly model what happens in the field and on the watershed.  The person doing the modeling needs to know how accurate and how precise the model being used is, and which inputs to the model cause the largest changes to the model output.  When the most influential inputs are identified, more time and energy can be focused on measuring or estimating these inputs with a higher degree of accuracy.  This paper identifies the input values to a widely-used model, the Soil Water Assessment Tool (SWAT), that are most sensitive to predicting annual total water yield and surface runoff for the 1692-ha subwatershed known as “K” of the Little River Experimental Watershed.  The most sensitive model inputs are the soil curve number, a soil evaporation coefficient, and the available water content of the soil.
                                Technical Abstract: Water quantity and quality issues continue to be a concern on the Southeast Coastal Plain.  Changes to land management practices can conserve soil moisture and reduce sediment, nutrient, and pesticide loadings at the field scale.  The Soil Water Assessment Tool (SWAT) watershed scale model was used to simulate the hydrologic response of a 1692-ha subwatershed of the Little River in south-central Georgia over the 1995-2004 period.  The model overpredicted total water yields in 7 of 10 years, primarily due to overestimation of base flow, and underpredicted evapotranspiration.  Predicted surface runoff was estimated to within 3% of calculated values for the ten-year period.  Analysis of model input parameter sensitivity on annual total water yield and surface runoff was conducted for key hydrologic parameters within the LRW.  Additional work planned includes analyzing input parameter sensitivity for daily peak flows, calibrating the model for hydrology and chemical loading, and estimating the uncertainty in the model outputs.


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