Water Management Report for Cumberland River Basin

J. Percy Priest

As of 8 August 2007 J. Percy Priest was at elevation 489.4 ft., which is about 0.6 feet below the desired summer pool level. Due to the dry spring and continued drought conditions it has not been possible to fill the reservoir. Conditions within J. Percy Priest Lake are similar to those of the past. Little dissolved oxygen is present below 20 feet in most areas of the lake. Since recreation is a major project purpose, maintenance of the summer pool near 490 is an important goal.

Objectionable water quality conditions routinely exist in the J. Percy Priest tailwater when hydropower releases are made during the time the project is stratified (May-November typically). Anoxic conditions in the lake result in high levels of iron and manganese. The iron usually precipitates (falls) out of the water quickly, however the remaining manganese makes the water appear nearly black and is more difficult for downstream water users (Metro Nashville Water Services) to treat. Also, objectionable odors (like rotten eggs!) are caused by the gas hydrogen sulfide. This gas is generated by bacterial metabolic action in the anoxic, lower portion of the lake.

The inability to fill the reservoir has precluded the commencement of a continuous, non-power, minimum flow release into the tailwater. There is simply not enough water flowing into the lake to maintain the lake's elevation if a continuous flow sufficient to provide real improvement of conditions in the tailwater were undertaken. Unfortunately, the tailwater area immediately below J. Percy Priest Dam looks very unsightly with large areas of dry river bed punctuated with essentially stagnant water. Very little water leaks through the dam to provide a flow.

Lack of spring rains prevented the filling of J. Percy Priest Lake. So far in 2007, it has not been possible to implement a continuous minimum flow that would have prevented the unsightly conditions in the immediate area below the dam without serious impacts on upstream lake levels.

An added attraction below J. Percy Priest Dam is the new Stones River Greenway. Visitors using the greenway this year unfortunately are seeing an aquatic environment that is highly stressed. The situation in the tailwater contrasts greatly with 2006 when continuous flows were made using a spillway gate. The release greatly improved tailwater river corridor aesthetics and the aquatic environment. Barring some event that provides enough water to fill the reservoir, it is unlikely the continuous release will be possible this calendar year. An environmental restoration project is underway at J. Percy Priest Dam to open an existing conduit through the dam which would provide the flows previously supplied by opening a spillway gate. Construction work to complete the new release works should be underway this fall with completion in time for next years summer season.