The best time to stop a flood is before it starts, right? That’s exactly what TVA tries to do.
TVA uses its network of dams to reduce flood damage by holding back the water from heavy rains in reservoirs. These “flood-storage” reservoirs (usually located on “tributary rivers” — rivers that run into the main Tennessee River) do most of the work in controlling floods.
Big storms — the ones that can cause flooding — are most likely to hit the Tennessee Valley in the winter and early spring. So, to make room for this water in the flood-storage reservoirs, TVA lowers their water levels by January 1 each year. The water in tributary reservoirs can rise and fall as much as 60 feet per year.
When a storm hits, TVA holds the water back by closing the gates of the dams in areas where it is raining. When the rain stops and the danger of downstream flooding is over, TVA lets the water out at a gradual rate to get ready for the next storm.
As you might expect given how much it rains, there were lots of floods in the Tennessee Valley before TVA dams were built. These floods washed away the topsoil, causing problems for farmers. Even worse, hundreds of people died and thousands more lost their homes and farms. The city of Chattanooga, Tennessee, would flood about once a year.
Today, TVA’s system of dams and reservoirs prevents about $260 million in flood damage along the Tennessee, Ohio, and Mississippi Rivers every year. Read more about flood management.
When most people are sound asleep, at least three TVA employees are sitting in front of their computers watching for storm systems; checking information about rainfall and stream flows; and trying to predict how much water is flowing into each TVA reservoir. Then, when a storm hits, they’ve got to make some quick decisions about how much of the flood water to store in one reservoir or another.
Sometimes, tough judgment calls are required. Should TVA hold the water back to prevent minor flooding downstream, or release water from the reservoirs to be sure there’s enough space to store more rain if it comes?
It’s a lonely spot to be in—especially in the middle of the night when TVA workers have to make the call that will affect so many people. In every case, TVA’s top priority is public safety. Read more about TVA's River Forecast Center.