Flood Control

TVA uses 34 dams to control flooding by holding back the water from heavy rains in reservoirs. Flood-storage reservoirs on the tributary rivers — those that flow into the main Tennessee River — do the bulk of the work in controlling floods.

TVA prepares for the “flood season” by lowering the level of these reservoirs so they can store the runoff produced by rain and snowfall. This stored runoff is later released at a controlled rate and used to facilitate navigation, generate electricity, support water-based recreation, and enhance water quality. In the summer, when the flood risk is lower, TVA keeps tributary reservoir levels up to support recreation.

Big storms are most likely to hit the Tennessee Valley in late winter and early spring. To make room for this water in the flood-storage reservoirs, TVA lowers their water levels by December 31 each year. These reservoirs may rise and fall from eight to 50 feet over the course of a 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.

Flooding was a serious problem in the Tennessee Valley before the TVA dams were built. Casualties were high, and many people lost their homes and farms. Because of poor farming practices, these floods washed away the topsoil, causing severe erosion and limiting farmers’ ability to grow crops. Malnutrition was widespread.

Today, TVA’s system of dams and reservoirs prevents about $200 million in flood damage in the Tennessee Valley and along the Ohio and Mississippi Rivers every year.