HYDROLOGIC SIMULATION OF THE LITTLE WASHITA RIVER EXPERIMENTAL WATERSHED USING SWAT

Authors: Van Liew, Michael; Garbrecht, Jurgen

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2001
Publication Date: 1/15/2003
Citation: Van Liew, M.W., Garbrecht, J.D. Hydrologic Simulation of the Little Washita River Experimental Watershed Using SWAT. Journal of the American Water Resources Association. 2003. v. 39(2). p. 413-426.

Interpretive Summary: In recent years computer programs have been developed to determine how changes in land use or climate impact runoff and groundwater on a watershed Computer programs used for these kinds of studies contain parameters that describe the watershed properties such as vegetative cover, soil characteristics, or landscape features. These parameters must be given watershed specific values to accurately simulate runoff from that watershed. This process of assigning appropriate values is referred to as model calibration. Once a hydrologic model is calibrated, it should also be tested on different data sets in a process referred to as model validation. Validation is used to verify that the model has been properly calibrated. A study was conducted to calibrate and validate a computer model referred to as the Soil and Water Assessment Tool (SWAT) on the Little Washita River Experimental Watershed (LWREW) in Southwestern Oklahoma. The calibration involved a two-step process. A preliminary calibration was conducted to establish good agreement between observed and simulated yearly and monthly runoff. Parameters in the model were then fine-tuned based on measured daily runoff. Calibration of the model on a daily basis resulted in a better match between the measured and simulated runoff than was obtained in the preliminary calibration. Results from this study show that for the most part SWAT simulated runoff responses reasonably well over a range of hydrologic conditions for the validation periods. Results indicate that the model is capable of providing reasonably accurate simulations for hydrologic studies related to the impact of changes in land use and climate fluctuations on water availability of the LWREW.

Technical Abstract: Precipitation and runoff data from two subwatersheds within the Little Washita River Experimental Watershed (LWREW) in Southwestern, OK were used to evaluate runoff prediction capabilities of the Soil and Water Assessment Tool (SWAT). Over six years of precipitation and streamflow record were used to calibrate parameters that govern surface and subsurface runoff response in the model, and over nine years of available record were used for subsequent model validation. Calibration of the two subwatersheds involved a multi-step process. A preliminary calibration was conducted to estimate model parameters so that the measured versus simulated yearly and monthly runoff depths were in agreement for the respective calibration periods. Model parameters were then fine-tuned based on a visual inspection of daily hydrographs and flow frequency curves. Calibration on a daily basis resulted in higher baseflows and lower peak runoff rates than nwere obtained in the preliminary calibration. Test results from this stud show that for the most part SWAT predicted runoff responses reasonably well over a range of hydrologic conditions for the validation periods. Results of this investigation indicate that the model is capable of providing reasonably accurate simulations for hydrologic studies related to the impact of changes in land use, management, and climate fluctuations on water budget and water availability of the LWREW.