Lake Conroe is a man-made lake constructed in 1973 along the West Fork of the San Jacinto River. It is a water supply reservoir, meaning that water levels are maintained as close to the permitted normal pool level as possible to assure the largest supply of water in times of drought. What it also means, however, is that there is little storage space for storm water.
The lake’s normal pool elevation is 201 feet above mean sea level (msl). An automated network of real-time rainfall and stream flow monitoring stations continuously observes the rainfall and lake level. The State permit for Lake Conroe requires that any waters above elevation 201 must be “passed through” the reservoir by releasing it through one or more of the five gates. During a storm event, if rising water is not released at the proper rate by allowing it to pass under the bottom of the gates, the gates can be overtopped risking failure of the structure. The excess waters released through the gates flow down the West Fork of the San Jacinto River. The gates are situated at about the center of the dam, which sits at the southern end of the lake.
It’s important to realize that even when the gates are releasing water, the dam still temporarily holds back a significant amount of water, therefore reducing downstream flooding.
Pre-releasing water prior to a storm event is not an approved practice for Lake Conroe (or for most water supply reservoirs in Texas) for a number of reasons. Doing so would cause the streambed to fill prematurely. Then, even a very small amount of rain could cause the river to flow out of its banks unnecessarily. In addition, it would take several weeks to safely release enough water to make a meaningful impact in a storm. Pre-releases would need to occur for weeks to lower the lake level significantly, which is well beyond the range of accurate weather forecasting.
Did you know?
The length of the dam is approximately 11,000 feet. Each gate is 40 feet wide, so the gates cover an area of the dam 200 feet long. When the lake reaches the 201-foot elevation, the gates are raised to keep water from spilling over them. Water is then released from beneath the gates.