District Digest News Stories

Water managers test water quality during Hydropower operation

Nashville District Public Affairs
Published Nov. 11, 2014
Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam  during a test of the dam's hydro power generator.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam during a test of the dam's hydro power generator.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two water quality multi-parameter signs into the tailwaters to collect, record water quality, check water temperatures, dissolved oxygen, conductivity and monitor pH levels at the J. Percy Priest Dam, Nov. 10, 2014.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam  during a test of the dam's hydro power generator.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam during a test of the dam's hydro power generator.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam  during a test of the dam's hydro power generator.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District logs data collected by two water quality multi-parameters Monday, Nov. 10, 2014 at the J. Percy Priest Dam during a test of the dam's hydro power generator.

HERMITAGE, Tenn. (Nov. 12, 2014) -- Water quality experts from the U.S. Army Corps of Engineers checked water quality conditions in spillway and hydropower release from J. Percy Priest Dam Nov. 10, 2014.

Hydropower releases from J. Percy Priest were discontinued in late May due to low dissolved oxygen conditions which had developed in the lake.  Since then releases from the dam have been made through the spillway gates and the fixed-cone valve.  This has allowed Corps water managers to manage the lake level and to release water with good dissolved oxygen levels.

Mark Campbell, a hydrologist in the Water Management Section, Nashville District used two multi-parameter water quality instruments to collect key water quality data from the Stones River just downstream of J. Percy Priest Dam.  These instruments allowed him to assess temperature, dissolved oxygen, specific conductance, and pH conditions in the releases from the dam. 

“This is our standard procedure to evaluate water quality conditions at our projects,” said Campbell.  “The information that we collect is used to make real-time water management decisions on how to release water from the different dams that make up the Cumberland basin reservoir system,” said Campbell.   He said, “It is important that the water we release from our dams supports the needs of fish and aquatic life.”

According to Campbell, spillway and fixed-cone valve releases are effective means of supporting the downstream environment, but there are trade-offs when releasing water in this manner.  Turbulence associated with these releases results in hazardous conditions near the dam.  Also, power production is discontinued when water released from the dam does not pass through the hydropower turbine.  Spillway gate and fixed-cone valve releases have been used to improve water quality in the summer and fall below J. Percy Priest Dam for several years.

Unlike turbine releases which are relatively calm, spillway gate and fixed-cone valve releases are quite turbulent and can be a hazard for boaters directly below the dam.  Boaters are encouraged to avoid the area and to always wear life jackets while on the water.

According to Campbell, a series of natural processes occur in J. Percy Priest Lake during the spring and summer that result in depleted oxygen levels in the deeper portion of the lake.  The water stratifies, or separates into two distinct layers separated by a transition zone know as the thermocline.  The warmer surface layer stays in contact with the atmosphere and maintains relatively dissolved oxygen concentrations.  The colder deeper layer is cut off from the atmosphere so that once oxygen is depleted it is not restored until the fall when cooler air temperatures start a mixing process in the lake. 

Water passed through the hydropower turbine originates from fairly deep in the lake.  Usually by the middle of May water quality in the lake has degraded to the point that hydropower releases can’t meet water quality standards and are suspended.  Spillway gate and fixed-cone valve releases pull better quality water from higher in the water column.  Then, when released into the river, additional oxygen is added to the water due to the turbulence associated with these releases.

In response to recent colder air temperatures the mixing process in the lake is now well underway.  This is responsible for improved water quality conditions that Campbell observed in the lake and in the river below the dam.  His testing found that water released through the turbine would support downstream fish and aquatic life. This has allowed the spillway gate releases to be discontinued an now all water is being passed through the hydropower turbine, producing electricity in the process. 

Water quality conditions are different at each dam, therefore, the Corps uses a wide range of methods to improve dissolved oxygen concentrations in project releases.  In some cases, more than one approach is necessary to reach oxygen targets, which vary depending on the type of fishery present in the tailwater. 

The Nashville District has a hydropower modernization initiative underway that will include aeration features on replacement turbines where dissolved oxygen concentrations are a concern.  This will allow Corps water managers to better meet environment requirements and will result in more hydropower generation.

The public can obtain news, updates and information from the U.S. Army Corps of Engineers Nashville District on the district’s website at www.lrn.usace.army.mil, on Facebook at http://www.facebook.com/nashvillecorps and on Twitter at http://www.twitter.com/nashvillecorps.