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Flood control vs. water supply vs. recreation

The reservoirs in the Brazos River Authority system are great places to have a little aquatic fun. But some people might be surprised to know that when these lakes were planned and built, recreation was not their primary purpose. Instead, their creators designed them to either tame Texas’ sometimes raging rivers or to supply water to a thirsty, growing population.

Texas was not blessed with a wealth of natural lakes. Only one, Caddo in East Texas, was naturally created with a dam added in the early 20th century. The rest were built to serve a purpose such as flood control, water conservation or a combination of both. No lake has a constant level, and knowing why a lake was built can help one understand why lake levels can vary.

Flood Control

The Brazos River’s history, like that of other waterways around the state, was periodically marked by devastating floods that took numerous lives and destroyed homes, businesses and agricultural land. In response to those floods, the state legislature formed the Brazos River Conservation and Reclamation District, the Authority’s predecessor, to “tame” the river and alleviate flooding throughout the Brazos basin.

Major flooding elsewhere around the United States prompted Congress to pass the 1944 Flood Control Act, which tasked the U.S. Army Corps of Engineers (Corps) to build reservoirs around the nation to alleviate flooding. Among other places, the Corps went to work on the Brazos and its tributaries. Over the next few decades, the Corps built several flood control lakes in the Brazos basin, including Whitney, Georgetown, Stillhouse Hollow, Belton, Granger, Proctor, and Somerville lakes.

With these lakes, the Corps added a concept known as the “flood pool.” Dams for flood control lakes are built much larger than those used on water supply reservoirs. These lakes are normally kept at a level that allows the dam to hold an extended capacity during heavy rains that might otherwise flood the area. The added room in this flood pool allows flood water to be captured and stored until it may be released downstream in a safe manner.

Water Supply

In the 1950s, Texas, like much of the nation, suffered under what was at the time the worst drought on record. It became clear to officials that more reservoirs would be needed across the state to help ensure a water supply during dry periods.

In the Brazos basin, the Authority has built two lakes with the primary purpose of water supply, Limestone and Granbury. These lakes are designed to store water for drinking as well as agricultural, industrial, environmental, recreational and other uses. Possum Kingdom, the Authority’s first lake when it was finished in 1941, was built in part to produce hydropower. Today is serves primarily as a water supply reservoir.

During periods of drought, such as much of Texas saw over the last couple of years, lake levels can drop as the rate of evaporation increases with the summer heat and the demand for water goes up. Though it can be frustrating for those who use or live near the lakes to see the water recede, the lakes are actually serving their purpose as designed.

Combination

Texas lakes often serve a dual purpose. Many flood control lakes also hold a water supply. However, supply lakes are not necessarily built to aid in flood control. While the three Authority lakes are used as storage reservoirs, they are not designed to provide flood control.

The Authority’s continuing relationship with the Corps, however, provides examples of dual-use lakes. Though the Corps lakes were built to prevent flooding, the Authority contracts with the federal government for storage in each of these bodies of water. The area where water supply is stored at a flood control lake is known as the conservation pool.

The flexibility of the lakes in the Brazos River basin ensures that they will continue to meet Texans' needs, whether in times of drought or flood.