The network of submerged oxygen diffusers, which cost $11.3 million to design and build, went online for testing last June and is fed by two above-ground, 20,000-gallon tanks near Modoc, S.C.
Its purpose is to improve water quality in the lower end of the lake during hot weather, when elevated surface water temperatures drive striped bass upstream in search of cooler, oxygenated water.
Those fish often congregate in the tailrace of Russell Dam, where there is more oxygen, but where the dam’s reversible turbines have been shown to kill fish and raise water temperatures in the lake.
During startup testing last year, the system consumed about 5,100 tons of oxygen, costing $395,000, corps spokesman Billy Birdwell said.
A 2012 procurement notice issued this week seeks providers for 5,000 tons, with the option to add 2,000 tons if needed.
Jamie Sikes, the corps’ district fisheries biologist, said the system will be used as needed from June through September, when a phenomenon known as the “thermal squeeze” affects Southeastern reservoirs and their large sport fish.
As warm weather heats the lake, surface water becomes too hot for stripers and the cooler layers of water below become nearly devoid of dissolved oxygen.
The diffusers, placed at depths of 80 to 120 feet about five miles upstream from Thurmond Dam, help oxygenate that cooler, deeper water to provide a suitable hot-weather habitat that keeps the fish from migrating upstream.
Though data are still being gathered and evaluated, tests were conducted last year using stripers tracked by radio transmitters.
“We know from the early results that there were striped bass that stayed down in the lower portion of the lake all summer,” Sikes said.
In addition to holding stripers in the lower end of the lake, oxygenating the deeper layers of water improves water quality in the Savannah River below Thurmond Dam.
The system is part of the plan under which Russell Dam was allowed to become fully operational. The corps agreed in 2002 that only two of the four reversible units would be operated during warmer months to avoid heating up the tailrace area and disrupting striper activities.
The successful operation of the oxygenation system will allow the corps to operate all four pump back units year-round, allowing water from Thurmond Lake to be reused for hydropower production.