Water Quality Modeling of Bosque River Watershed to support TMDL Analysis

Abstract

The State of Texas has identified a number of water bodies having water quality problems andclassified them for Total Maximum Daily Load (TMDL) development. A TMDL program hasbeen initiated for the North Bosque River Watershed in Texas, USA, where point and nonpointsources of pollution are of a concern. Impairment was determined under narrative water qualitycriteria related to excessive aquatic plant growth.<br><br>A watershed modeling approach was used to quantify the effects of phosphorus control measureson stream water quality. The watershed simulation model, Soil and Water Assessment Tool(SWAT), was validated for flow, sediment, and nutrients. The validated model was applied toquantify the effects of management practices related to dairy manure management and municipalwastewater treatment plant effluent. This paper describes the impact of these practices onphosphorus. The benefits of phosphorus control measures for wastewater treatment plantsresulted in greater improvement in stream concentrations, while control measures on dairiesmade greater difference on phosphorus loadings. Results were used to inform the TMDLstakeholder group of possible controls that could reduce phosphorus loadings and concentrationsin the Bosque River Watershed. This SWAT application and these assessment methods areadaptable to similar TMDL/water quality projects in other parts of the United States.