Tennessee Valley Authority
Reservoir system update
Thunderstorms and showers this spring and summer have brought relief from the longstanding dry conditions in the Tennessee Valley.
Fort Loudoun Reservoir
For the calendar year to date (Jan. 1-Sept. 1), the Valley has received about 34 inches of rain, which is 94 percent of normal. Runoff is 89 percent of normal.
Rainfall in the eastern Valley — the area above Chattanooga — also has returned to near normal for the year (97 percent), but runoff amounts are only 83 percent of normal, indicating that groundwater is still recharging after several years of drought conditions.
Runoff is important to reservoir elevations because it is a measure of the water that reaches the river system when it rains instead of being absorbed into the ground. Runoff is affected by soil conditions and by the intensity, amount, and duration of rainfall.
Because rainfall has been near normal since Jan. 1, TVA was able to fill the reservoir system to target levels on schedule and to keep reservoirs within their targeted elevation ranges through the summer.
Tributary reservoir elevations
Reservoir |
Observed Elevation* |
Flood Guide Elevation* |
||
Sept. 1, 2008 |
Sept. 1, 2009 |
Sept. 1 |
Jan. 1 |
|
South Holston |
1698.9 |
1723.6 |
1729 |
1708 |
Watauga |
1943.6 |
1953.6 |
1959 |
1952 |
Cherokee |
1050.9 |
1062.4 |
1069 |
1045 |
Douglas |
970.3 |
985.9 |
991.5 |
954 |
Fontana |
1675.4 |
1696.7 |
1702.5 |
1653 |
Norris |
1000.4 |
1012.4 |
1020 |
1000 |
Chatuge |
1920.4 |
1922.6 |
1923.4 |
1918 |
Nottely |
1765.5 |
1770.8 |
1772 |
1762 |
Hiwassee |
1498.7 |
1511.3 |
1513 |
1485 |
Blue Ridge |
1675.4 |
1680.9 |
1682 |
1668 |
*In feet
On Sept. 1, 2009, the 10 largest tributary storage reservoirs were an average of 12 feet above their level on the same date in 2008.
“Reservoir levels dropped gradually in August, but that’s typical,” says TVA’s Chuck Bach, manager of River Scheduling. “Our system flow requirement goes up on August 1 because river temperatures gradually increase as the summer progresses. Providing more flow in late summer helps to keep the water from becoming too warm, which, in turn, helps to protect aquatic habitat and water quality. In years with normal rainfall and runoff, there’s enough inflow to make up for much of the water released to meet the higher flow requirement, so there’s less impact on reservoir elevations. But this year, the drop in reservoir levels was more noticeable because we’re still catching up on runoff.”
Even so, August elevations were within the targeted range and much higher than they were in 2007 and 2008, according to Bach.
“After three years of drought, we’ve had a little more water to work with this summer,” he says. “We’ve been able to keep reservoir elevations up for recreation, and we’re in a much better position to supply hydro generation this fall.”