Tennessee Valley Authority
Reservoir Operating Guides
TVA uses reservoir operating guides to make decisions about moving water through the Tennessee River system. These guides show typical reservoir elevations throughout the year (expressed as the number of feet above sea level), as well as when the spring fill and winter drawdown are scheduled to occur. They help ensure there's enough room in the reserovirs for flood storage while also providing for hydropower generation, navigation, water quality, recreation, and other benefits.
Operating guides are based on many decades of operating experience. They take into consideration all the features that influence a reservoir’s ability to store and release water—the size and shape of the surrounding watershed, the reservoir’s surface area, and the average rainfall and runoff—as well as historical demands for water use and flood storage space at different times of the year.
Tributary reservoir operating guides
Operating guides for tributary reservoirs typically consist of two lines: a flood guide and a balancing guide.
The flood guide is a seasonal elevation guide that shows the amount of storage allocated in a reservoir for flood damage reduction. The operating objective is to keep the reservoir below this line. The reservoir level at the dam may rise above the flood guide line as a result of large inflows, but the level is lowered to the flood guide line as soon as it can be done without increasing downstream flood damage.
The balancing guide is used to ensure that water is drawn from tributary reservoirs equitably when water must be released from the reservoirs during the summer to meet downstream flow requirements. The operating objective is to keep the elevation of each reservoir similar relative to its position between the flood guide and the balancing guide.
Main-river reservoir operating guides
Operating guides for reservoirs on the main Tennessee River typically depict the top and bottom of the normal operating zone for multiple system benefits, including flood damage reduction. The top of the normal operating zone is often exceeded, however, for the temporary storage of high flows.