WATERSHED ANALYSIS TO IDENTIFY WATER QUALITY IMPROVEMENT POTENTIAL AND SPECIFIC SITES FOR STREAM AND WETLAND RESTORATION

The Charlotte Area local watershed plan (LWP) was developed for the North Carolina Wetlands Restoration Program (WRP) (recently renamed the Ecosystems EnhancementProgram) in conjunction with local stakeholder agencies in Charlotte and Mecklenburg County, North Carolina. LWPs are developed by NC WRP with funding provided by the North Carolina Department of Transportation (NCDOT) for the purpose of developing watershed plans within hydrological units where NCDOT projects are or are projected to have significant impacts. In addition to developing plans to exisitng improve and future watershed conditions, the LWP process is geared to identify restoration sites to meet mitigation needs in a way to provide the most benefit to improving water quality.The LWP development included development of a GIS-linked database; a detailed assessment of exisitng land use, water quality, biological, and habitat; development/refinement of new and exisitng HSPF watershed models; screening process to identify focus areas within the watersheds for detailed field investigations; field studies that included geomorphic and habitat assessments of identified stream reaches, delineation of potential wetland restoration sites, and verification of potential retrofit sites for BMPs; data analysis and ranking of potential projects for focus areas; development of capital improvement plans based on the ranking; determining stream, wetland, and “watershed approach” mitigation potential for the recommended projects; and a comprehensive LWP with recommendations for local program modifications to protect stream uses. The mitigation potential based on the “watershed approach” uses recent guidance from the Army Corps of Engineers where stream restoration mitigation credit can be achieved through implementation of a combination of stream restoration and BMP type projects.The focus areas identified represent 7 percent of the total watershed areas and were selected to demonstrate the water quality improvement that could be achieved if restoration activities were focused in small catchment areas. This effort has shown that a combination of BMP and stream/wetland restoration projects within the focus areas can reduce annual sediment loading in the range of 30 to 50 percent within the focus areas. This includes estimated reduction from streambank erosion, which was evaluated during field investigations using the Bank Erosion Hazard Index (BEHI). The stream and wetland projects recommended have the potential to provide 60,000 linear feet of stream mitigation credit and 10 acres of wetland credit in the focus areas. An additional 29,000 linear feet of stream credit is potentially available through the implementation of BMPs.The focus area analyses and the modeling of future land use water quality with and without various controls has demonstrated that water quality targets can be achieved through a combination of efforts. Implementing post-construction runoff control requirements, which in NC included a requirement to control 85 percent to the total suspended sediment from new development, were identified as a critical factor in meeting future water quality targets.