CREATIVE WATERSHED PERFORMANCE REQUIREMENTS FOR NEW DEVELOPMENT
Gwinnett County's Watershed Protection Plan represents the culmination of a two-year watershed assessment and modeling project. As part of the project, an integrated assessment of the habitat, biological community, water quality, and pollutant loadings in the streams was used to
assess both the current and the future impacts on the streams and their uses. The BASINS modeling framework was used to model the watersheds under existing and future land use conditions. The integrated assessment of these impacts was the key to developing an effective, efficient watershed
protection and improvement strategy.
The Watershed Protection Plan incorporated a three-pronged approach to protecting and improving the County's watersheds:
New development requirements are implemented to protect watersheds from
Improving previously affected areas will allow aquatic integrity to improve.
Related activities that improve the effectiveness and scope of watershed improvement (such as conservation zoning, stream
buffers, maximum limits on parking spaces, etc.) are recommended.
The focus of this paper is on the first item—development and implementation of new development requirements.
In areas where water quality criteria provide little practical guidance
for developing watershed protection plans, statistical relationships between biotic integrity (benthos, fish, and habitat scores) and pollutant loadings for key parameters in kg/ha/yr (lb/ac/yr) were used to develop watershed improvement guidelines. An automated spreadsheet
analysis tool (WISE) was used to facilitate this analysis and allow interactive evaluation with the County and citizens' group.
There are three basic strategies available for new development requirements: voluntary, proscriptive, and performance-based. Because performance-based strategies
provide needed protection as well as maximum flexibility for the development community, the focus of this strategy is performance-based. An approach is presented that is simple to use and encourages site design that takes advantage of the natural site amenities and minimizes impervious surfaces.
Options are provided for implementing BMPs on the site and designating the tributary 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.
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