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In 2000, the Gwinnett County Department of Public Utilities (DPU) completed a Watershed Protection Plan (WPP) in accordance with the Georgia Environmental Protection Division (EPD) permitting requirements for a new or expanded wastewater National Pollutant Discharge Elimination System (NPDES) discharge permit. The WPP recommended improving impacted areas and protecting streams by completing detailed Watershed Improvement Plans (WIPs).

CH2M HILL completed a WIP for the Chattahoochee River tributaries in Gwinnett County. The Chattahoochee River Tributaries study area encompasses 106 square miles and approximately 614 stream miles. The overall goal of this project is to identify and implement actions that 1) enhance the aquatic integrity of impaired streams within each study area, 2) return these streams to their designated uses, and 3) remove them from EPD's 303(d) list.

Within the framework of this goal, the objectives of this project are to:

Evaluate existing stream conditions, determine causes of stream degradation, and identify opportunities for stream restoration.

Identify riparian-floodplain areas and opportunities to expand these areas for habitat improvement, flood reduction, and sediment storage.

Inventory existing storm water BMPs and identify retrofit or new BMP opportunities that would mitigate urbanization-caused changes in runoff volume and timing.

Evaluate the benefits of watershed BMP and stream restoration projects.

Estimate costs of each potential project.

Prioritize projects using benefit/cost analysis, public input, and County resource availability.

Assist with public education efforts.

The first step toward justifying a dedicated funding source for storm water projects is to identify the scope and need for a comprehensive storm water program. The results of the WIP indicate the need for and expected costs of proposed projects essential to meeting multiple regulatory requirements. The total CIP costs for these study areas, combined with others in Gwinnett County, determine the range of expenditures needed to improve water quality and biotic integrity.

Because of the need to efficiently collect and manage large amounts of detailed information about conditions in the study areas, GIS and global positioning system (GPS) technologies were used. GIS tools combine database information with spatial information to help quickly visualize and quantify the location and extent of conditions in the study areas. Base data, such as watershed boundaries, infrastructure, political boundaries, and hydrology, were provided by the DPU and other County departments. These data were used to develop field plans and other new data needed for the fieldwork. These data were critical to the assessment and development of potential restoration and retrofit projects.

Field teams were equipped with handheld GPS units to gather data at the specific location of each problem or condition identified during the stream walk or BMP inventory. The GPS unit was connected directly to a handheld computer, which ran GIS compatible software. A database was developed with the software to store data points and develop GIS shape files that were used to display data and identify potential restoration/preservation projects. Field teams also documented stream and BMP conditions using a digital camera and noted the location of each photograph in the GIS database.

A list of potential BMP retrofit and stream restoration projects was developed from the BMP inventory and pedestrian survey. Each potential BMP project was identified as a retrofit or new construction project to provide peak flow reduction, water quality, and/or channel protection benefits. Each potential stream restoration project was assigned a recommended level of restoration and associated restoration measures considering 1) the extent of degradation of the stream channel and buffer, and 2) the potential for recovery based on several factors, including physical constraints, stream type, and property ownership. Each potential stream and BMP project was scored and ranked based on TSS and habitat benefit-cost ratios. A GIS based model was developed and used to predict TSS loading rates for each stream reach and associated TSS removal efficiencies for each project. The higher-ranking projects were included in each CIP.

The complete list of ranked potential projects was reviewed and evaluated to develop a final CIP for the study area. Projects were selected for the CIPs to reduce the TSS yield from all stream reaches within the watersheds below 1,600 lb/ac/yr. Highest-ranking headwater or upstream projects were selected first, and projects downstream were then selected iteratively using the GIS-based model until the TSS yields from all reaches were predicted to be below 1,600 lb/ac/yr based on implementation of the projects. The CIP projects were presented and grouped into two levels of service:

Regulatory: projects that are needed to reduce the HUC 12 watershed TSS yield below 1,600 lb/ac/yr.

Reach: to reduce each stream reach (i.e., 20-ft segment) TSS yield below 1,600 lb/ac/yr.
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Document Type: Research Article

Publication date: 2005-01-01

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