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Current Lake Level Conditions from TVA
Although the Midwest has been besieged by tragic storms and flooding of historic proportions, the Tennessee Valley once again has not had any significant rainfall during the previous week. For the week ending June 13, there was an average of 0.39 of an inch of rainfall recorded in the Tennessee Valley. Runoff was 0.09 of an inch. (Note: The rainfall and runoff data included here is as of midnight June 12.)
Fair conditions with more normal temperatures were forecast for this week. A chance for rain was forecast for the end of this week as weak disturbances rotate around the base of a trough that was expected to form over the eastern part of the country.
Severe to extreme drought conditions continue to persist across northern Alabama, Georgia, eastern Tennessee and North Carolina. A sustained period of above-normal rainfall is needed to break the drought in the eastern portion of the Valley. Typically, this time of year, only the tropics can provide that amount of rainfall.
Below is information on the condition of the reservoir system as of June 13.
For the calendar year-to-date (Jan. 1-June 12), the Valley has received a total of 19.63 inches of rainfall and 10.19 inches of runoff. Rainfall for the calendar year-to-date is 79 percent of normal. Hydro production for the calendar year-to-date is 57 percent of normal.
The pool levels at South Holston, Watauga, Cherokee, Douglas, Fontana, Norris, Chatuge, Nottely, Hiwassee and Blue Ridge are all below flood-guide levels and are expected to remain there through this week.
TVA will continue to schedule flows through the system to conserve water in storage and fill tributary projects when possible while meeting downstream flow requirements, maintaining water quality, protecting aquatic habitat and providing for commercial navigation
Why can't TVA keep lake levels up year-round?
Before the dams in the TVA system were built, just about every major storm resulted in serious flood damage to homes and businesses along the river. Now, most of this damage can be avoided by closing upstream dams and holding back the stormwaters until the danger of flooding is over. But for this to work there has to be room in the reservoirs to hold the extra water.
How does TVA make this room? You guessed it: by lowering the water level before the “flood season” begins. Just as you let water out of the bathtub by opening the drain, TVA can open gates in the dams to let water out of the reservoirs.
Why do TVA reservoirs have to be lowered so early?
TVA tries to keep reservoir levels as high as possible during the summertime so people can enjoy water sports. Keeping reservoir levels up even longer would make a lot of people happy, especially those who have homes on the lakefront, boaters, and people who make a living from recreation, such as marina owners. But TVA also has to think about some problems that might happen.
TVA's plan for lowering the reservoirs is based on rainfall records that have been kept for many years. These records show that big storms that produce floods are most likely to hit the Tennessee Valley in the winter and early spring. So TVA makes sure the reservoirs are lowered to “flood-control levels” by January 1. Those levels are low enough to leave room in the reservoir for rainwater to flow in.
TVA starts lowering reservoirs around Labor Day because it wouldn’t be a good idea to let out a whole lot of water very fast. A certain amount of water has to be kept in the reservoirs for other things like running the turbines in the dams that make electricity, giving fish enough water to live in, and keeping the water deep enough to float the big barges that travel up and down the Tennessee, Ohio, and Mississippi rivers.
So what would happen if TVA waited to start lowering reservoir levels?
A lot depends on the weather! If a major storm hits before TVA has time to make room to store the extra water, more flooding would be likely. Also, the price people pay for electricity could be affected. To make room for the stormwater, TVA would have to let the water out of its reservoirs fast — so fast, in fact, that it couldn’t be released through the turbines. That would mean less water for making electricity.
In very dry years, waiting to lower reservoir levels also could affect conditions for fish and other living things in the water and reduce water depths for barges on the Ohio and Mississippi Rivers