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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Swat for the Little River Experimental Watershed: Work in Progress

Authors
item FEYEREISEN, GARY
item STRICKLAND, TIMOTHY
item BOSCH, DAVID
item POTTER, THOMAS
item Sullivan, Dana
item Wauchope, R - USDA-ARS-SEWRL-RETIRED

Submitted to: Soil and Water Conservation Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 6, 2006
Publication Date: October 11, 2006
Citation: Feyereisen, G.W., Strickland, T.C., Bosch, D.D., Potter, T.L., Sullivan, D.G., Wauchope, R.D. 2006. Evaluation of swat for the little river experimental watershed: work in progress. Managing agricultural landscapes for environmental quality: strengthening the science base workshop [abstract]. Soil and Water Conservation Society Proceedings.

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 The purpose of the present research is to estimate the effectiveness that conservation practices have in improving stream water quality in the Coastal Plain. Questions being asked include: “What effect does cropping system change have?”; “What effect has conservation tillage had to date? What would be the impact of increasing conservation tillage in the future?”; “What happens to pesticides that are applied to the cropping systems in the Coastal Plain?”. The method of research involves the use of the measured field and stream information to calibrate computer simulation models, which mimic the response of the natural landscape to management and climate changes. Very detailed information about soil properties under conventional and conservation tillage, obtained from a field-scale experiment, is used in analysis of watersheds with areas of 6.4 square miles and 130 square miles. The model predicted results are compared to measured results to check accuracy of stream flow and stream chemistry, and to provide feedback for improvement of the simulation model.

Technical Abstract: The Soil and Water Assessment Tool (SWAT) was manually calibrated to simulate the hydrologic budget components measured for the 16.9 km2 subwatershed K of the Little River Experimental Watershed (LREW) near Tifton, GA from 1995 to 2004. A local sensitivity analysis indicated that the most sensitive parameters for total water yield (TWYLD) were curve number for crop land (CN2), soil available water content (SOL_AWC), and soil evaporation compensation factor (ESCO). The most sensitive parameters for stormflow were curve number for crop land, curve number for forested land, soil bulk density (SOL_BD), and soil available water content. Correcting the seasonal flow discrepancies and trimming the high peak predictions after long dry spells would improve the hydrologic modeling efficiency and enhance the model for future water quality simulation. SWAT, parameterized in one watershed for a particular time period and run on a nearby watershed and for a different time period, predicted hydrologic response satisfactorily. Monthly Nash-Sutcliffe model efficiencies for TWYLD were 0.79 and 0.79 for the calibration and validation watersheds for the same time period, respectively. SWAT was also found to simulate hydrology and stream chemistry (N, P, pesticides) responses directly comparable to those produced by the Pesticide Root Zone Model (PRZM).

Last Modified: 9/29/2014
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