Gwinnett County Watershed Improvement Plans

Client: Gwinnett County

Location: Gwinnett County, GA

Summary: Cardno ENTRIX, Inc. has worked on four watershed improvement plans, covering over 200 square miles of the County for Gwinnett County since spring 2002. These plans are being developed for the Department of Water Resources to prioritize storm water projects and improve existing conditions within each of these watersheds as outlined in the watershed protection plan. Watersheds in the county are mostly highly developed, and as a result, the streams are degraded due to non-point source pollution (i.e. sediment) and altered hydrology.

A significant component of the improvement plans is to evaluate the conditions of the streams in each watershed to identify potential sources of sediment and prioritize areas for rehabilitation and restoration. Cardno ENTRIX is the lead firm for conducting the stream restoration task in all three projects, which involves walking all streams in each watershed to quantify stream bank erosion throughout the study area, identifying illicit discharges, and completing a Rosgen stream channel classification to assist with developing restoration plans. Information from the stream walks is used to prioritize areas within the watersheds to identify retrofitting opportunities or new storm water best management practices (BMPs). To date, Cardno ENTRIX staff has walked over 600 miles of streams for these projects.

Once BMPs and stream restoration projects have been identified, projects are evaluated based on a cost/benefit analysis to determine the best mix of projects to recommend to the County that are aimed at improving the physical, chemical, and biological integrity of the watersheds. Besides technical feasibility, each project is evaluated for water quality benefits, protection value, habitat and biological integrity, hydrologic control for both flood and channel protection, and implementation issues (e.g., County program compatibility, Neighborhood acceptance and O & M). In addition, some projects are considered maintenance issues for the county, and these projects are consolidated into a maintenance database to include in its existing county maintenance program.

Improvement to the watersheds from recommended projects are quantified and related to the overall watershed management goals developed as a part of the watershed assessment. Projects are ranked based on a scoring system and cost comparison. Final costs and projects are presented to the County in the form of a detailed capital improvement plan to be considered by the Board of Commissioners for future funding.