Modeling the Lake Eucha Basin with SWAT 2000

Lake Eucha is first in a complex of two lakes. The second, Spavinaw Lake, is used as a watersource by the City of Tulsa. Taste and odor problems made the water very expensive orimpossible to treat in recent years. The source of these problems is thought to be algal bloomsdue to elevated nutrient concentrations in Lake Eucha. In a previous modeling study of thebasin, we supported claims that the application of poultry manure was responsible for increasedphosphorus load to Lake Eucha. We prepared a new model including more water quality andflow data, recent land cover data derived from Landsat TM+ imagery, high resolution (Nextgeneration weather radar) NEXRAD precipitation data, and soil test phosphorus for bothpastures and row crops. The Soil and Water Assessment Tool (SWAT) 2000 model wascalibrated for flow at three gages and for phosphorus loads at eight locations. Phosphorus loadswere estimated using the US Geologic Survey (USGS) program LOADEST2 using observedwater quality measurements, and streamflow estimates provided by both the City of Tulsa andthe USGS. The SWAT model predicts that the application of poultry litter and elevated soil testphosphorus in the basin is responsible for 49% of the current annual phosphorus load to thelakes.