Scaling up the SWAT model from Goodwater Creek Experimental Watershed to the Long Branch Watershed

The primary model selected for use in the Conservation Effects Assessment Project-Watershed Assessment Study (CEAP-WAS) was the Soil and Water Assessment Tool (SWAT) model. The first objective of the study was to calibrate and validate the SWAT model to simulating stream flow and sediment yield for the Goodwater Creek Experimental Watershed (GCEW), a 70 km2 watershed located in north-central Missouri, using the SSURGO and the STATSGO soil data sets. The model performed well in simulating stream flow, particularly on an annual and monthly basis. The study showed that the performance of the model in simulating stream flow using the STATSGO soil data was as good as that using the much more complex SSURGO soil data. The second objective of the study was to evaluate the performance of the model calibrated for GCEW using the STATSGO data set in simulating stream flow for the Long Branch watershed, a 462 km2 watershed containing the GCEW and draining into Mark Twain Lake within the Salt River Basin. The performance of the model in simulating stream flow from the Long Branch watershed was as good as that from GCEW. For the Long Branch watershed, the 9-yr (1995-2003) average simulated annual stream flow was less than 4% higher than that measured, and the ENS and r2 values were 0.97 and 0.94 for annual stream flow and 0.79 and 0.77 for monthly stream flow, respectively. The model did not perform as well in simulating stream flow on a daily basis but its performance was similar in the GCEW and Long Branch watersheds. Future plans include: (1) to evaluate the parameters that influence the flow component of the model to determine if daily stream flow simulation could be improved, (2) to calibrate the pesticide component of the model, and (3) to perform further calibration of the sediment yield component of the model, once the sediment load computation process from GCEW is completed. When these steps are completed, simulation for 12 other watersheds on the Salt River Basin will be done.