Despite a common misconception, there are very few “constant level lakes,” and none operated by the Brazos River Authority.  A constant level lake is one that is artificially managed to remain at a specific level essentially by using another source of water to replenish losses due to evaporation, etc.  

Several factors can affect a lake’s level and only some are within human control. The chief factor that is not controllable is the impact of climate.  Evaporation is a constant, natural part of the water cycle that causes the liquid form of water to change into gas or vapor and move into the atmosphere reducing the amount of  water in a lake.

During periods when outdoor temperatures rise, the rate of evaporation increases. During periods of drought the effect is even more dramatic.

As temperatures rise, increased demand by residents, agriculture, cities, industry, power plants and others on water stored can also draw down a lake’s level.  This impact is exacerbated during periods of extended drought.

Though it can be frustrating for those who live near Texas lakes or turn to them for recreation, dropping lake levels during a drought are also a sign that a reservoir is successfully meeting one of its basic obligations: supplying water to thirsty Texans during a time of need. 

Constant level is a term given to the practice of maintaining a body of water at a specific elevation.  No natural body of water has a constant level.  While some fluctuate more than others, all natural bodies of water change on a daily basis, some rapidly during floods.  Few man-made reservoirs have the ability to be maintained at a constant level as evaporation, drought, water use and/or flooding affect elevation levels. 

The height above mean sea level that water in a reservoir has reached. Brazos River Authority and U.S. Army Corps of Engineers lakes are actually reservoirs, or parts of the Brazos River basin impounded by dams. (A free-flowing river is measured in stages, that is, by depth from the river bed to the surface.)

Sedimentation in water treatment is a process in which water is cleaned by allowing solids to settle out of the water by gravity during treatment.

Releases are made for several reasons including water supply for users near the lake and downstream, to pass through water released from another system reservoir, or to refill storage in a downstream reservoir.

For a look at current lake levels, click here.   

Periodically, officials conduct a survey of lakes within the Brazos basin to determine each lake’s volume. As part of that work, survey crews determine each lake’s depth (in feet). Do not confuse this measurement with lake level, however.

A lake’s depth is the distance from the lake’s bottom to the top of the conservation pool, the point where the lake is considered full. The lake level is the number of feet the surface is above mean sea level. 

Crews use a combination of GPS technology and sonar to find the lake’s depth at various points to get an average to determine volume. The sonar sends sound waves to the lake bottom at different frequencies, and the results are compared to help also determine how much sediment has collected. The surveys also find each lake’s deepest point, which is typically near the dam.