Drawdown of TVA Reservoirs Follows Labor Day
September 4, 2009
After the Labor Day weekend, TVA will begin drawdown of the tributary reservoirs on the Tennessee River system to reach winter levels by Jan. 1.
Tributary reservoirs are drawn to their lowest level to get ready for flood-producing storms. These storms typically occur in winter and early spring when vegetation is dormant and runoff into the Tennessee River system is highest.
Water levels on the tributary reservoirs this year were at normal summer levels, allowing for recreation on all of the Tennessee River system reservoirs. For the calendar year Jan. 1 through Aug. 31, rainfall in the eastern Tennessee Valley, the area above Chattanooga, returned to near-normal with 34.6 inches of rain, which is 97 percent of normal. Runoff this year is 83 percent of normal, indicating that ground water is still recharging after about three years of drought conditions. In comparison, last year’s rainfall was 79 percent of normal and runoff was 51 percent.
Runoff is important to reservoir levels, because it is a measure of the water that reaches the river system during rainfall instead of being absorbed into the ground. Runoff is affected by soil conditions, plant abundance and the intensity, amount and duration of rainfall.
“Reservoir levels dropped gradually in August, but that’s typical,” said River Operations Senior Vice President Janet Herrin. “Our system flow requirement increases on Aug.1 because river temperatures tend to rise with the air temperature, and we need to provide more flow to protect aquatic habitat and water quality and provide cooling water for power plants.”
As part of the Reservoir Operations Study implemented in 2004, TVA restricts how much water is released from the tributary reservoirs from June 1 through Labor Day, so there is more water for recreation. Throughout the summer, TVA releases water from upstream reservoirs to protect aquatic species and meet other downstream needs.
Herrin said all tributary reservoirs are drawn down proportionately as TVA maintains flows throughout the system. “We draw water from the tributary reservoirs in a balanced manner so the impacts on any one reservoir are minimal,” she said.
Water levels on the main Tennessee River reservoirs are near normal. Those reservoirs do not fluctuate as much as the tributary reservoirs, because they have less storage space and the main river channel must always have water deep enough to accommodate commercial barge traffic.
TVA is the nation’s largest public power provider and is completely self-financing. TVA provides power to large industries and 158 power distributors that serve approximately 9 million consumers in seven southeastern states. TVA also creates economic development opportunities and manages the Tennessee River and its tributaries to provide multiple benefits, including flood damage reduction, navigation, water quality and recreation.
Barbara Martocci, Knoxville, (865) 632-8632
TVA News Bureau, Knoxville, (865) 632-6000