Abstract:
Heated discharges from thermal generating plants in Canada which employ once-through cooling will increase dramatically during the remainder of this century. The impact of these discharges on natural waters is difficult to determine because such effluents typically consist of large volumes of moderately heated water, the effects of which are not easily measured. The method of estimating the effects of heated discharges upon an aquatic ecosystem is to monitor several physical, chemical and biological parameters for the purpose of developing converging lines of evidence ot indicate what may be happening. The Manitoba Hydro Brandon Generating Station is a 237 MW, fossil-fuel, peaking facility with a cooling water pumping capacity of 200 cfs. Various amounts of cooling water are removed from the adjacent Assiniboine River, warmed, and then returned. The data recorded in this study includes mean monthly flow rates in the Assiniboine River at Brandon; upstream, downstream and discharge temperatures from the point of thermal discharge into the Assiniboine River; diversity indices for benthic macroinvertebrate communities at designated sampling stations upstream and downstream from the thermal effluent outfall. Mean monthly flow rate data for the Assiniboine River at Brandon between 1953 and 1969, prior to flow control regulation by the Shellmouth Reservoir control installation, indicated that the flow rates were often less than the 200 cfs pumping capacity of the Brandon Generating Station cooling water pumps... The diversity index values representing benthic macroinvertebrate communities did not uncover evidence of degredation to the ecosystem attributable to the thermal effluent. More knowledge of the mixing patterns of the thermal effluent in the receiving waters is required, however, so that biological samplers can be installed in and out of those waters influenced by thermal discharge temperatures.
