Alcovy Watershed Assessment: Simulating Best Management Practices and Future Development Using the BASINS Framework

The Alcovy River watershed (312 square miles) spans Gwinnett, Walton, Newton and Jasper counties which are served by the Northeast Georgia Regional Development Center. The Northeast Georgia RDC has taken a proactive stance in protecting the Alcovy River watershed. In anticipation of significant growth and protection of valuable water resources, the group has requested the preparation of the Alcovy River Watershed Assessment Report and the Alcovy Watershed Protection Plan. This project discusses the modeling portion of these larger studies. The purposeof this study was to develop a calibrated watershed water quality model in order to simulate the impact of different future scenarios. The BASINS interface to HSPF was selected as the watershed water quality model for the Alcovy River watershed. Water, sediment, phosphorus and fecal coliform were the constituents modeled. The hydrologic portion of the model was calibrated to continuous daily USGS flow data available at a station on the Alcovy River. In-stream water quality data used for the model were obtained from four USGS stations located on the Alcovy River and fifteen additional stations located throughout the study area. Upon completion of calibration, the model simulated the impact of future development using a projected land cover for the year 2020 and increased loads from point sources. Eight future scenarios incorporating various management practices were modeled. These scenarios include the simulation of conservation subdivisions, riparian buffer ordinances, impervious surface restrictions, storm water quality controls and improved enforcement of erosion and sedimentation controls. Model simulations indicate that the phosphorus load nearly doubles for almost all future scenarios as compared with current conditions. Furthermore, no single management practice indicates a significant pollutant load reduction. Sediment and fecal coliform results showed similar trends. Modeled results indicate that a combination of best management practices must be implemented in order to achieve any noticeable reduction in pollutant loading to the Alcovy River. This hydrologic and water quality model demonstrates that the anticipated growth and development will be detrimental to the water quality of the Alcovy River watershed. If only the BMPs simulated for this project are considered, it is expected that the degradation of water quality will be slowed, but not eliminated.