HSPF Modeling of Nonpoint Sources in Tickfaw River Watershed

The Tickfaw watershed is located in southeastern Louisiana with the Tickfaw River originating in Southern Mississippi, flowing through St. Helena and Livingston Parishes, and eventually emptying into Lake Maurepas. The total drainage area is 1,896 km2. Forests cover 66% of the watershed and agriculture is the second predominant land use type. The elevation of the watershed changes from 0 m above sea level in the south to 130 m in the north. According to the 2004 Louisiana Water Quality Inventory report section 303(d), outstanding natural resource and secondary contact recreation designated uses are fully supported, but fish and wildlife propagation and primary contact recreation are not supported. According to the 303(d) list, the impairments in Tickfaw River are mercury, total dissolved solids, fecal coliform, phosphorus and dissolved oxygen. There are many suspected sources of impairment, including agriculture, construction, forest management, and industrial sources. The goal of this study is to make use of a Geographic Information System (GIS), the EPA\u27s BASINS tools, and the HSPF water quantity and quality modeling program to quantify and differentiate the sources of pollution that arise from storm water runoff coming from agriculture, forestry, and other sources. This will allow the Louisiana Department of Environmental Quality (LADEQ) personnel to better focus implementation efforts on those areas and practices that appear most critical to water quality problems. In the process, a water quality model has been calibrated and validated for annual flows; seasonal flows and for water quality parameters like dissolved oxygen, nitrogen and phosphorus. An assessment analysis was performed to determine the loading of nitrogen and phosphorus coming from each land use. Various land use scenarios were created in Tickfaw watershed and total loading resulting from these landuses were integrated with the watershed’s subbasins in the GIS for graphical presentation. These landuse scenarios were also ranked based on its resultant total loading. Based on these loading rates, total loading of nitrogen and phosphorus resulting from these land use scenarios were significantly higher when current landuse was converted to cropland and pasture, thereby adversely affecting the water quality in rivers