Managing river flows
Managing the flows within the rivers that pass through Alabama Power’s 14 dams and 11 lakes is a crucial part of harnessing the renewable power of water. This third installment of Dam Anatomy takes a closer look at how these resources help managing shifts in flows caused by the state’s sometimes unpredictable rainfall.
All of the Alabama Power-managed rivers and dams operate under a federal license, which along with the authority given to the company by the U.S. Army Corps of Engineers provides guidance for how we store and release water. These operating guidelines outline a predetermined schedule, known as a guide curve or rule curve.
In times of heavy rains, may increase these levels, or in times of abnormally dry conditions, which may drop lakes below normal levels — Alabama Power has responses in place to help reduce the impact. These extreme times are generally known as flood control or drought mitigation.
Water management and dam operation go hand in hand.
Before Alabama Power’s dams were built, many of the state’s rivers were known for their wild unpredictability. The lakes created by the company’s dams were designed to minimize the impact of the large volume of water from heavy rains.
Certain lakes — called storage lakes — were designed with flood control as a purpose. These lakes are drawn down each fall to make room for the normally heavier winter and spring rains, which in turn help refill them to normal summer pool levels during the late spring.
As a part of its flood control capacity, Alabama Power also relies on its right to manage water above normal rule curve levels on property surrounding storage lakes when managing large-volume flows. Alabama Power’s Smith, Weiss, Neely Henry, Logan Martin, Harris and Martin lakes are considered storage lakes.
Other lakes, called run-of-river lakes, were designed to pass heavy flows downstream and have limited flood control capability. Alabama Power’s run-of-river lakes have levels that vary little throughout the year and include Lay, Mitchell, Jordan/Bouldin, Yates and Thurlow.
When rains fall short of expectations — resulting in drought conditions — Alabama Power works to balance the needs of lake and river stakeholders in impacted watersheds.
Alabama Power hydrologists use rainfall and seasonal climate predictions to model potential short- and long-term impacts to the lakes and river systems. If predictions and modeling suggests that drought impacts could cause lakes not to fill, the company — along with state and federal regulatory agencies — can request a temporary increase in winter pool levels on the storage lakes most likely to be affected as well as reductions in downstream minimum flow requirements.
During drought conditions, Alabama Power works to balance the impact of scarce resources among all stakeholders — leading to lower lake levels, reduced downstream water releases and decreased power generation at company dams.