Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007
geographic location for a “put and take” trout fishery, which is stocked by both the South Carolina and Georgia Departments of Natural Resources. Decreasing summertime dissolved oxygen levels in the lake due to thermal stratification have historically impaired this fragile downstream fishery when water is released during generation periods. Working with the Tennessee Valley Authority (TVA), plant staff modified turbines adding hub baffles and air passages to significantly improve downstream water quality. Before the installation of the hub baffles, less than 1 mg/L dissolved oxygen discharge was common in the tailrace during August and September. The turbine hub baffle modification increased release dissolved oxygen as much as 3 mg/L with a measured efficiency loss of 0.5% at maximum wicket gate opening.
Richard B. Russell Project is a pump storage facility and the middle Corps impoundment on the Savannah River. One of the environmental features installed during initial construction was a forebay hypolimnetic oxygen diffuser system to meet downstream water quality standards. Liquid oxygen is trucked to a local storage facility and a water bath vaporizer is used to gasify the oxygen before distribution into the lake. The original system consisted of a rigid pipe grid supplying oxygen to ceramic and rubber diffuser membranes. This system required periodic underwater cleaning and leveling to achieve better oxygen dispersion. TVA developed an improved efficiency replacement system which was installed at Richard B. Russell in 2002. The TVA-designed diffuser lines have controllable buoyancy, enabling surface inspection and maintenance, thus eliminating need for divers or remote operated vehicles. The improved oxygen transfer efficiency of this new system is yielding equivalent water column dissolved oxygen absorption while using only 60% of the liquid oxygen requirement of the previous diffusers.
J. Strom Thurmond Project is the oldest and southeastern most Corps hydropower facility on the Savannah River. In conjunction with the rehabilitation of the 50-year-old power plant, the Corps installed Auto-Venting Turbines (AVT) designed and manufactured by Voith Siemens Hydro. Unlike conventional Francis turbines, AVT blades are hollow with thicker leading and trailing edges. Air is channelized under the headcover to the hollow turbine blades. Air and water mix at the blade’s trailing edge that is machined with slots to facilitate air passage. The turbine efficiency impact of the AVT is only 0.2% with one air passage valve open improving discharge dissolved oxygen by 2 mg/l. At Thurmond, AVT has increased downstream dissolved oxygen as much as 4 mg/l. The AVT provides greater dissolved oxygen absorption with a wider distribution filling the draft tube cross section. This action earned the Corps and Voith Siemens the 2003 National Hydropower Association Hydro Achievement Award.
Over the next few years the Corps will automate dissolved oxygen systems, optimize multiple aeration systems, pursue real time turbine efficiency and water quality monitoring. The Corps is beginning installation of a new oxygen diffuser to mitigate for habitat loss and eliminate hydropower operational restrictions in the basin. These accomplishments and plans demonstrate only a fraction of the commitment with which the U.S. Army Corps of Engineers views the mission of environmental stewardship. The Savannah District is extremely proud of the ecological improvement successes realized within our region and look forward to meeting similar challenges in the future. ________________________________________________________________________
Session 9 – Page 5