IMPLEMENTING WATERSHED MANAGEMENT RECOMMENDATIONS THROUGH STORMWATER MASTER PLANNING IN GWINNETT COUNTY, GEORGIA

Gwinnett County, like many suburban areas near Atlanta, is experiencing rapid population growth and corresponding changes in land use. These changes dramatically affect the character of many of the County's watersheds. The State of Georgia recently began requiring watershed assessments, and corresponding watershed protection plans, to help mitigate the secondary impacts of development on the health of its lakes and streams.In early 1998, the Gwinnett County Department of Public Utilities (DPU) began a comprehensive watershed assessment project covering all 437 square miles of the County. The project's major components are watershed characterization (including habitat, benthos, fish and water quality monitoring), watershed modeling (using BASINS), watershed protection, and public involvement. Currently, all tasks in the project are complete and the County is moving toward implementing recommendations of the watershed protection plan.One key component of the watershed protection plan is the development and implementation of requirements for new development in the watershed. Performance-based strategies were used to provide needed protection as well as maximum flexibility for the development community. A site-specific guideline for TSS was developed and a spreadsheet tool that assists with new development layout to meet the target was developed. Options are provided for implementing Best Management Practices (BMPs on the site and designating the contributory drainage area to each BMP. The form automatically graphs and compares the uncontrolled and controlled loading rates to the performance criterion. This tool can be used iteratively in the site design process.In addition to the new development tool, which focuses mainly on water quality controls, Gwinnett's regulations were also revised to control water quantity from new development including four key hydrologic design events – 1) major flooding (100-year), 2) out of bank flooding (2-to 25-year), 3) channel protection (1-year) and 4) water quality (1.2 inch rainfall). These design events are managed to protect the environment and the public. In combination with the BMP form, these strategies provide needed protection to steams as well as maximum flexibility for the development community.In watersheds where new development requirements were not sufficient to meet watershed improvement guidelines, phased stormwater master planning is used to address improvements to current conditions in the watersheds and to develop a capital improvement plan that will help improve water quality within the watersheds to meet watershed improvement guidelines and address current TMDLs. The major components of the stormwater master plan involve 1) a flood study, 2) infrastructure inventory, 3) BMP analysis, and 4) stream restoration.This paper presents a method for prioritizing subwatersheds to focus stream restoration recommendations and develop water quantity and quality BMPs to improve watershed biotic integrity. Data characterizing stream habitat quality, Rosgen stream channel classification and stream bank erosion are collected along the study area steams. The information is then used to prioritize subwatersheds to focus stream restoration and structural BMP recommendations. This information is the used to develop conceptual plans for improvements as part of the stormwater master plan. Recommendations are modeled to demonstrate attainment of watershed improvement guidelines and development of the capital improvement plan.