Balancing Fisheries Management and Water Uses for Impounded River Systems

Conduct of a Reservoir Multimetric Bioassessment to Address a Clean Water Act Section 316(a) Demonstration for Georgia Power Company’s Plant Branch, Lake Sinclair, Georgia

Terry E. Cheek, Anthony R. Dodd, Ronald G. King, Scott Hendricks, and Bill Evans

doi: https://doi.org/10.47886/9781934874066.ch43

Abstract.—A multimetric reservoir bioassessment was conducted on Lake Sinclair, a 6,204-ha multipurpose impoundment in central Georgia in 2002. This bioassessment was the first application of such techniques on a reservoir in Georgia and was an integral component of a Clean Water Act Section 316(a) demonstration. Findings from this project were used to support a request for a thermal variance for the Plant Branch heated discharge. Plant Branch is an electric generating facility that withdraws water from Lake Sinclair for cooling purposes and discharges heated effluent to the reservoir under the authority of a National Pollutant Discharge Elimination System permit. A new cooling tower system began operation in 2002 and was designed to remove approximately 50% of the thermal output from the plant during summer months. Subsequently, the bioassessment was conducted to determine if a balanced, indigenous aquatic community is protected and maintained in the thermally influenced portion of Lake Sinclair.

Detailed habitat characterization was performed within thermally influenced areas (Primary Study Area [PSA]) and references areas of the lake to identify major habitat types and select comparable sampling sites. Fish community sampling was conducted on a seasonal and spatial basis via nighttime electrofishing, experimental-mesh gill netting, and seining within the PSA and comparable sites outside of thermally influenced areas (reference areas). Hydroacoustic surveys were also conducted to assess abundance, vertical and longitudinal distributions, and movement of limnetic fishes reservoir-wide and in response to the thermal discharge. The macroinvertebrate community was sampled seasonally using Hester-Dendy artificial substrate samplers, dip nets, and petite Ponar grab samplers in littoral/sublittoral zones in the PSA (8 sites) and in the reference areas (16 sites). The condition of the Primary Study Area biological community was scored against the reference condition in Lake Sinclair as a measure of the expected, best attainable condition in the absence of thermal influences related to Plant Branch.

Based on site-specific biotic integrity classifications developed for Lake Sinclair, the Primary Study Area metric scores determined for critical summertime conditions (index period) totaled 53 points for the macroinvertebrate community and 43 points for the fish community (each score based on a 60-point scale), equating to integrity classifications of “Very Good” and “Good,” respectively. This indicated that conditions in the Primary Study Area were comparable to those found in the reference areas of the reservoir. Results of this bioassessment demonstrated that the protection and propagation of a balanced, indigenous aquatic community is being maintained in the thermally influenced Primary Study Area of Lake Sinclair. Notably, such conditions were supported during a time of extended drought, above normal air temperatures, and high electrical demand. Thus, the bioassessment indicated that operation of the Plant Branch facility does not have an appreciable impact on the biological community of Lake Sinclair.