Field Experiences in Improving Water Quality Downstream from Dams

摘要

Recent experiences by the Tennessee Valley Authority in improving water quality and fish habitat downstream from dams are presented. At Douglas Dam, floating pumps near the surface of the large, thermally stratified reservoir are being used to move surface water, high in oxygen content, into low level hydroturbine intakes to increase the dissolved oxygen content of the turbine discharges. Historically, the area near the mouth of the Little Tennessee served during the summer months as a cold water refuge for fish. The closure of Tellico Dam diverted the entire Little Tennessee flow via a canal into Fort Loudoun Reservoir for power generation through Fort Loudoun Dam turbines. This flow diversion eliminated the refuge. To reestablish the refuge, a siphon was installed to maintain a flow of cold water over Tellico Dam and an underwater rock barrier was constructed downstream to create a cool water pool. At Upper Bear Creek, air was forced through diffuser pipes near the bottom of this relatively small, flow-through reservoir to oxygenate and precipitate iron and manganese before discharge through the dam.