Alabama Power manages the rivers and streams that pass through its 14 dams and 11 lakes, stretching across the Coosa, Tallapoosa and Black Warrior rivers. Managing these flows is challenging and complex.
The floods in December are a recent example of Alabama Power’s flood control systems in operation. The rains spread over 10 days from Dec. 21 – 30, with the heavier downpours during the six days from Dec. 21-26 serving as the driving force of the event.
Many of Alabama Power’s storage reservoirs increased to levels well above summer pool levels and into the flood easements. Smith Lake was rising 1 foot per hour during the peak flow period, which occurred about 6 p.m. on Christmas Day.
The maximum volume of water stored in the flood pools (that is, winter pool to maximum elevation reached during flood event) of Smith, Weiss, Logan Martin, Harris and Martin during the event totaled about 50 billion cubic feet, equivalent to about 400 billion gallons of water.
That amount of water would cover all of Alabama’s 52,419 square miles with about Â½ inch of water. It would fill:
- the Great Pyramid in Giza, Egypt 19,000 times
- the Empire State Building in New York City 1,500 times
- the Georgia Dome in Atlanta 680 times
- the AT&T Stadium, home of the Dallas Cowboys, 500 times
“To put the amount of water released in perspective, maximum releases during the event from the Coosa and Tallapoosa were 2.5 times the annual average flow at Niagara Falls, and very near the annual peak flow at Niagara Falls. This volume of water would be enough to completely fill the Georgia Dome in about six minutes or the AT&T stadium in Arlington in about nine minutes,” says Alan Peeples, Alabama Power’s reservoir management manager.
Managing river flows in Alabama
All of the Alabama Power-managed dams operate under federal licenses that, along with the authority given to the company by the U.S. Army Corps of Engineers, provide guidance for how we store and release water. These operating guidelines outline a predetermined schedule, known as a rule curve or flood control guide curve.
“Rainfall directly affects this ability to operate according to the set rule curve. In times of heavy rainfall, flows from the rains may increase these lake levels or in times of abnormally dry conditions, lack of flow from lack of rain may cause the lakes to drop below their normal seasonal levels. Alabama Power has procedures in place to help manage the impact, whether high or low,” Peeples says.
Flood control for Alabama’s lakes
Flood control can be defined as minimizing river stages most often downstream of a dam, but also can apply to within the reservoir itself. Downstream flood peaks are minimized by discharging less water than is coming into the reservoir, resulting in rising lake elevations; all of this is by design. Through the operation of its dams, Alabama Power is able to minimize the impact of the large volume of water from heavy rains.
Certain lakes, known as storage lakes, are designed with flood control in purpose. These lakes are drawn down each fall to make room for normally heavier winter and spring rains, which in turn help them to reach normal summer pool levels during the late spring. Smith, Weiss, Neely Henry, Logan Martin, Harris and Martin are all considered storage lakes.
As part of flood control, Alabama Power maintains the right to manage water above normal rule curve levels during times of flooding on properties surrounding storage lakes. Most flood control reservoirs have a control point that is used as a focus for the flood control operations; for example, Neely Henry uses Gadsden, Harris uses Wadley, and Smith uses Cordova.
Run-of-the-river lakes pass the flows coming into them directly downstream and do not have flood control capacity. The lakes include Lay, Mitchell, Jordan, Bouldin, Yates and Thurlow and have levels that vary little throughout the year.
“Not every flood can be completely controlled. Each project has a particular amount that it can store,” Peeples says.
In times of less rainfall and when we are in drought conditions, Alabama Power balances the needs of lake and river stakeholders in impacted watersheds. Engineers model potential short-and long-term impacts to the reservoirs based on seasonal climate and rainfall predictions. If predictions and modeling suggests that drought impacts could cause the lake not to fill toward summer pool, the company, with approval of state and federal agencies, can take measures such as reducing downstream minimum flow requirements to help minimize the impacts to the lakes and other resources.
From Alabama Power’s inception, hydro generation has been an integral part of how the company serves its customers. Not only was it the beginning of Alabama Power but it was the beginning of electricity in the state. Since Lay Dam began operating on April 12, 1914, the story of hydro generation has continued to affect Alabama beyond providing electrical service, including flood control, recreational and economic opportunity, irrigation and drinking water, and fish and wildlife habitats.
Hydro generation is one of the ways Alabama Power provides clean, safe, reliable, affordable energy for customers and communities both near the lake and. It is the lowest-cost energy source available on the system; harnessing the power of falling water is a self-reliant process that doesn’t depend on other systems or fuel infrastructure.
In a state with more than 77,000 miles of rivers and streams and 500,000 acres of standing water, dams play a complex role that impacts economic development, quality of life and conservation statewide.