Submitted to: ASABE Annual International Meeting
Publication Type: Abstract Only
Publication Acceptance Date: December 21, 2009
Publication Date: N/A
Interpretive Summary: Abstract Only.
Technical Abstract: The Fort Cobb Reservoir, which is within the Fort Cobb Reservoir Experimental watershed (FCREW) in Oklahoma, is on the Oklahoma 303(d) list (list of water bodies that do not meet the water quality standards as given in the Clean Water Act) based on sedimentation and trophic level of the lake associated with phosphorus loads. Nitrogen is also of concern in some stream segments in some seasons. Impairment of the lake for municipal water supply, recreation, and fish and wildlife are important factors in local economies and a high priority quality of life issue for community inhabitants. As a result the FCREW, one of the benchmark watersheds of the Conservation Effects Assessment Project which seeks to quantify environmental effects of USDA and other conservation programs, was selected for in-depth study. The Soil and Water Assessment Tool (SWAT2005) is a continuous-time physically-based watershed-scale model developed to predict the impact of land management practices on water, sediment, and agricultural chemical yields in watersheds with varying soils, land use, and management conditions over time. The level of uncertainty of input parameter values associated with hydrologic modeling has a significant impact on the simulation accuracy and the uncertainty of the resulting outputs. The objectives of this study were to: 1) investigate the effect of soils dataset resolution (STATSGO and SSURGO) on SWAT2005 sediment and total phosphorus simulation accuracy and outputs using four precipitation datasets, and 2) determine the best combination of soil-precipitation datasets for the Lake Creek sub-watershed within the FCREW. SWAT2005 was calibrated and validated for streamflow, sediments, and phosphorus for each of the soil-precipitation combination datasets using two soils and four precipitation datasets. The four sources of rainfall data included the National Weather Service’s network of Co-operative weather stations (COOP), statewide Oklahoma Mesonet (MESONET), USDA Agricultural Research Service’s weather station network (MICRONET), and NWS Next generation radar precipitation estimates (NEXRAD). The model performance was assessed using the Nash-Sutcliffe efficiency coefficient (NSE) and percent bias (PBIAS) statistics. Calibration and validation results and their discussion are presented in this study. Large differences in the simulated sediment and phosphorus yields and concentrations due to soils and precipitation dataset resolution could lead to significantly different outcomes in terms of the impacts of a given conservation practice for studies like CEAP. For this study sub-watershed, the SSURGO soil-MICRONET precipitation dataset combination consistently yielded the best simulation accuracy and is recommended for use in determining the impact of given conservation practices on water quality and quantity.