Heavy rains that result in flooding have become a sporadic occurrence on the Brazos River and throughout the state as the El Nino weather pattern lingers, drenching already saturated areas with even more water.
Recent rainy days have led some people to ask why the Brazos River Authority does not release water from its reservoirs in anticipation of possible precipitation. The short answer is that it is the policy of the Brazos River Authority to make releases based on the amount of water currently flowing in the river upstream, and not on weather predictions. Because weather forecasts are not always entirely accurate, the releases are made on verified water measurements.
Some have also asked if there have been changes in the release policy. Brad Brunett, water service manager for the BRA, said recent releases have been based on extremely wet weather, something that was very scarce in the Brazos River basin for several years leading up to the El Nino weather pattern that started in the spring of 2015. “We have not changed our operations procedures. What has changed is the return of wet weather.” Brunett noted. “We do make releases based up upstream gage flows in some cases, but there are other considerations as well, such as allowing for warning time downstream of the dam.”
While it may seem prudent to consider releasing water in advance if heavy rain is forecast, Brunett said in some cases that could actually cause more problems.
“The BRA does not ‘pre-release’ based on weather forecasts for a number of reasons,” he said. “Even with today's technology, meteorologists cannot precisely predict how much it is going to rain or exactly where it is going to rain, much less translate that into how much of the rain is going to runoff into a lake somewhere downstream.”
For example, sometimes widespread rain is predicted with a high degree of confidence. However, the precise locations and amounts are unknown. Rainfall can actually occur in areas where it was not expected, or an area may receive much less or much more rain than originally predicted.
“Trying to ‘out guess’ the rain can result in a number of problems, and the only sure thing is that you will be wrong,” Brunett said. He said if the BRA had started pre-releasing water trying to predict the rain, and then rather than excessive rainfall just upstream of a lake, it actually fell downstream on top of the water that was in the river from the pre-release, then the pre-release would have made downstream flooding worse. “On the other end of the spectrum, if the rain did not materialize as forecasted, water supply would have been wasted,” he said.
In some cases, people who are living in flooded areas downstream may wonder why more water needs to be released. Water supply dams are designed to hold a certain amount of water and they cannot hold more water without serious strain being placed on the dam. Not releasing water from the dam could actually cause more problems, such as structural failure that would actually cause much more water to flow downstream.
Another frequently asked question involves gates being “floated” at the Morris Sheppard Dam at Possum Kingdom Lake. Morris Sheppard Dam was constructed between 1938 and 1941. Each of the nine flood gates must be physically unlocked and “floated” before they can be lowered to release water. This is done by people actually using ropes and harnesses to climb onto the dam to prepare each gate before it may be lowered. It is accomplished much easier in favorable weather conditions. Once a gate is “floated” and unlocked, dam operations staff is able to quickly lower the gate if needed to release water. Therefore, it is much easier to prepare for possible releases by floating a gate and leaving it ready to be opened. Floating a gate is not the same as actually opening a gate.
The De Cordova Bend Dam at Lake Granbury and Sterling C. Robertson Dam at Lake Limestone were built with a different technology that does not require gates to be floated. The gates at those dams can be opened with the press of a button.
Updates of the release rates (measured in cubic feet per second) from each of the Brazos River Authority’s three reservoirs can be found on the Brazos River Authority website at brazos.org or by visiting the BRA’s Facebook page.
Gage readings measuring the streamflow in the Brazos River and its tributaries are available via reports from the United States Geological Survey (USGS) gaging stations in the Brazos River basin from Justiceberg in West Texas near Lake Alan Henry to the Rosharon area closer to the Gulf of Mexico are also available on the BRA website. To view the gages, go here and select the gage station or stations that you want to monitor.
The National Weather Service offers a Hydrologic Prediction Service that provides information about projections for water levels, including when an area of the river is expected to crest. The crest is the highest stage or level of a flood wave as it passes a particular point. Gauges along the river record the level of the water, and the highest level recorded at each gauge will be the crest for that gauge.
Links to the Hydrologic Prediction Service are available on the BRA website here.