SWAT Team Targets Water Pollution

By Don Comis
October 7, 2002

Rivers and lakes throughout the United States and world are kept cleaner with the aid of a computer model called SWAT, for Soil and Water Assessment Tool. Whether it's the Great Salt Plains Lake of Oklahoma--a shallow, briny lake that's an important way station for migratory birds--the Joanes River watershed in Brazil, or the Rio Grande watershed that spans eight states and parts of Mexico, water quality managers rely on SWAT to reduce the flow of silt, fertilizers or toxic chemicals into waterways.

Agricultural Research Service engineers Jeffrey G. Arnold and Kevin W. King and agronomist James R. Kiniry, all with the Grassland Soil and Water Research Laboratory in Temple, Texas, developed SWAT by assembling 30 years of ARS research data into an easy-to-use package. The key is an interactive color mapping software interface that enables managers to bring large, complex watersheds to life.

The maps pinpoint hot spots likely to be important sources of water pollution. The U.S. Environmental Protection Agency uses the model to set allowable pollution limits for 20,000 streams it has found to have poor water quality.

The SWAT model helps managers extend the life of reservoirs and cut their maintenance costs by reducing the amount of soil entering them. It has even been used in drought-stricken parts of Texas to increase streamflow by showing where to remove brush that was lowering water levels.

The model helps reduce farming's effects on waterways, whether that impact comes from pesticides and fertilizers in runoff from wheat fields of Oklahoma and Kansas washing into tributaries that feed into the Great Salt Plains Lake reservoir, or from large livestock feedlots polluting rivers that flow into downstream drinking water reservoirs. Excessive nutrients from fertilizers or manure cause algal blooms in waterways--or can even deplete the water of oxygen.

For more on the SWAT model, see the October issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.