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United States Department of Agriculture

Agricultural Research Service

Title: Validation of Hydrologic Response on Various Sized Watersheds Using Swat

Authors
item Van Liew, Michael
item Garbrecht, Jurgen

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: July 28, 2002
Publication Date: July 28, 2002

Interpretive Summary: Hydrologic simulation models are important tools for water resources managers. Simulation models used for studies in water resources 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. Of considerable interest to those involved in water resources studies is the question of applying a model calibrated on a particular watershed to smaller watersheds within that watershed or larger or adjacent watersheds with similar land use, soils, and geologic characteristics. This process is referred to as model validation. 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. Two subwatersheds within the LWREW (12.9 and 61.9 square miles in size) were used to calibrate parameters that govern the surface and subsurface runoff response in SWAT. The model was then applied to five other subwatersheds within the LWREW ranging in size from 1.1 to 236 square miles. Measured and simulated runoff agreed well on five of the seven subwatersheds. Less than satisfactory agreement on one of the subwatersheds was likely due to errors in the precipitation input on that watershed; overestimation of subsurface runoff on another subwatershed was due to the model's misrepresentation of ground water flow properties. Results of this study suggest that in most cases calibration parameters from one subwatershed in the LWREW can be used in other subwatersheds of varying size, and that subwatershed size had negligible impact on the performance of the model.

Technical Abstract: Accurate predictions of water budget and water availability for water resources investigations depend upon proper calibration and validation of hydrologic simulation models. In this study precipitation and streamflow data from seven subwatersheds within the Little Washita River Experimental Watershed (LWREW) in Southwestern, OK were used to calibrate and validate the performance of the Soil and Water Assessment Tool (SWAT). The LWREW was delineated into a number of subbasins, with the smallest subwatersheds consisting of only one subbasin and the largest consisting of dozens. Two subwatersheds within the LWREW (33.3 and 160 square kilometers in size) were used to calibrate parameters that govern the surface and subsurface hydrologic response in SWAT. The model was also applied to five other subwatersheds within the LWREW ranging in size from 2.9 to 610 square kilometers. Comparison of measured and simulated daily hydrographs and flow frequency curves shows that the calibrated model predicted peak flows, recession curves, and baseflows with reasonable accuracy on five of the seven subwatersheds. Less than satisfactory agreement on one of the small subwatersheds was likely due to errors in the input signal for precipitation on that watershed; overestimation of subsurface runoff on another subwatershed was attributed to the model's misrepresentation of shallow aquifer flow properties. Results of this study suggest that in most cases calibration parameters from one subwatershed in the LWREW can be used in other subwatersheds of varying size, and that subwatershed size had negligible impact on the performance of the model.

Last Modified: 7/31/2014
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