Ever wondered why the water at your favorite lake is often higher or lower than when you last visited?
Alabama Power operates two kinds of lakes: 1) Run of River, and 2) Storage. Lay, Mitchell and Jordan lakes on the Coosa River, Yates and Thurlow lakes on the Tallapoosa River, and Bankhead and Holt lakes (owned by the U.S. Army Corps of Engineers) on the Warrior River are called “run-of-river” projects that discharge essentially the same amount of water that flows into them. This type of operation gives them a fairly consistent lake level year round. These lakes were not designed with flood control as a specific project purpose. Alternatively, “storage” projects like Weiss, Henry, and Logan Martin lakes on the Coosa River, Harris and Martin lakes on the Tallapoosa River, and Smith lake on the Warrior (Sipsey) River provide seasonal storage, having different summer and winter pool levels, and are drawn down late fall into the winter to provide a means of managing and storing winter/spring rains. These operations provide a measure of protection against downstream flooding during high flow events. These storage projects normally have their levels returned to summer pool levels during the spring timeframe. Water stored in these storage lakes can also help mitigate some impacts of drought by providing a limited source of water for use when it is scarce, such as during drought periods.
The need for water in summer and fall can often exceed the natural supply. Most big lakes also operate for many other reasons — hydropower, recreation, navigation and the environment. Each of these purposes can factor into whether water is released, causing a fall in lake levels particularly during the late summer and fall periods.
Floods are normally the cause of the greatest and quickest changes in lake levels. Heavy rains produce floods that can raise a lake level several feet overnight. When floods are over, it is important to get the lake ready to store water from the next flood that may come along, and that is done by returning the lake to its normal level.