Evaluation and Spatially Distributed Analyses of Proposed Cost-Effective BMPs for Reducing Phosphorous Level in Cedar Creek Reservoir, Texas

Abstract

The assessment of BMP (best management practice) impacts using a watershed model has helped to establish a watershed conservation and protection plan that is projected to be required by government and decision makers. Cedar Creek watershed, located southeast of Dallas, Texas, was included in the 303(d) list as an impaired watershed due to high pH values. A number of efforts have been made to develop watershed protection plans by the North Central Texas Water Quality (NCTXWQ) project team. Tarrant Region Water District (TRWD) has monitored the water quality in the reservoir and found that chlorophyll-a has been increasing at an annual rate of 3.85%. Chlorophyll-a is a good indicator of algae growth, and TRWD, with 18 years of monitoring, revealed that the increase of chlorophyll-a needs to be a primary focus of the watershed protection plan. A stakeholder group and the project team suggested that total phosphorous (TP) reduction from the watershed should be targeted at 35% of current loading in order to preserve the water quality in the reservoir. In previous studies, flow and nutrients in the watershed were calibrated using SWAT (Soil and Water Assessment Tool). In addition, sensitivity analyses for each BMP were conducted such that each BMP was simulated in the model at a 100% adoption rate. The cost-effectiveness of each BMP was estimated and ranked by TP reduction. In this study, using the calibrated model and the cost-effectiveness analyses of the BMPs, the initially selected BMPs were simulated in SWAT to identify the reduction rate at the watershed outlet (reservoir) using a marginal adoption rate and to illustrate the spatially distributed impacts of each BMP at the subbasin scale. The results show that simulation of the eight selected BMPs in subbasins with higher TP loading can achieve the 35% reduction goal at the reservoir.