Rainfall Results in Increased Hydropower, More Water Moving through TVA Reservoirs

Nov. 24, 2009

Recent rainfall, combined with annual releases to lower reservoirs to winter levels, means TVA is generating more hydropower and moving more water through the Tennessee River system than normal.

TVA is generating hydropower at or above normal levels for the first time since 2006, thanks to above-normal rainfall in October.

“Hydroelectric plants at dams on the Tennessee River are generating at maximum capacity,” said TVA River Scheduling General Manager Chuck Bach. “Even so, we’ve had to release extra water at several main-river dams to keep tributary levels at normal stages to help prevent flooding.”

TVA’s objective is to make sure there is enough room in the reservoirs to store runoff from flood-producing storms that are most likely to occur between December and mid-April, Bach said.

“We can get heavy rainfall any time of year,” he added. “But winter storms tend to cover a larger area and can last for several days. Plus, vegetation is dormant, so we get more runoff.”

TVA begins releasing water from tributary reservoirs at a faster rate after Labor Day each year to prepare for the flood season. Reservoirs typically reach their lowest levels by Jan. 1 to allow for more storage space.

“That helps keep the water out of homes and businesses,” Bach said.

The changes in water levels can be dramatic. Fontana Reservoir, for example, fluctuates about 56 feet in a year to provide seasonal flood storage. By comparison, levels on main-river reservoirs change only 4 to 5 feet to maintain channel depths required for commercial navigation.

Bach said some people, especially newcomers to the Tennessee Valley, are surprised by the change in water levels. “People will buy a house on the water in the summer and not expect to see their dock on the ground in the winter,” he said.

The reservoirs in the Tennessee Valley are designed to function differently than natural lakes, said Bach.

“They were created by building dams, which allow TVA to adjust water levels to provide multiple benefits, including flood damage reduction, electricity generation, navigation, water supply and recreation.”

The system also allows TVA to respond to natural events such as floods and drought.

Starting the annual draw down of water after Labor Day gives TVA time to move the large volume of water through the system with less chance of flooding low-lying areas. It also allows TVA to use the water for hydropower.

“As we increase the amount of water we release, we use the water to spin turbines at TVA dams and generate electricity,” said Bach. “Of all the power sources, hydropower is the most efficient and economical.”

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.

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