It happens every year at this time, just like clockwork. The leaves change color and fall, the college football season is in full swing, and TVA tributary reservoirs are in the midst of the winter drawdown.
Lowering levels in the fall is part of the cyclical nature of reservoir management. During certain times of the year, reservoirs are held to higher or lower elevations—depending upon the relative risk from flooding during that particular season.
The timing of the drawdown is linked to the necessity of ensuring adequate flood storage space.
Historically, the months between December and April are when the Tennessee Valley experiences the greatest flood risk, due to storm front patterns and increased volumes of runoff. The focus is on drawing down the tributary reservoirs (since they hold the vast majority of flood storage space) in time to be ready for whatever lies ahead.
After the main flooding threat has passed, the season changes—and so do reservoir levels. The weather begins to warm, spring rains fall, the dogwoods start to bud, and lake levels begin rising. When possible, TVA restricts releases from the tributary reservoirs, in order to allow them to fill for the summer season. That time of year holds less risk from flooding, and the reservoirs are managed accordingly.
Full reservoirs, naturally, support a wide variety of recreational opportunities. But the same principle holds true during the annual winter drawdown: water released to maintain flood storage space also provides many other benefits—from hydropower generation to water supply to water quality.
While it’s true that lower reservoir levels aren’t exactly pretty, it’s also true that the resulting extra storage space is very much needed for flood damage reduction. Reservoir levels may be dropping at present, but it’s important to remember that this is just one part of the cycle. Not so very long from now, the day will come when the ground will begin to thaw, the daffodils will bloom, and raindrops will fall instead of snowflakes. And when spring comes to the Tennessee Valley, lake levels will start rising once again.