Everyone’s morning routines look slightly different. But something that most of us do before heading out the door for the day is to check the local weather report.
If it says “hot and sunny,” you’ll likely wear loose clothes and pack extra water to stay hydrated. If there is rain in the forecast, chances are you’ll bring an umbrella and raincoat with you. If it doesn’t rain that day, you may be annoyed that your carried extra items with you and you’ll have to water your lawn later. Or, if the forecast says sunny, then you’re caught in a downpour, you might begrudgingly toss your clothes in the dryer when you get home. Most people know that even with our current technology, weather can still be unpredictable and change in an instant, especially in Texas.
So, when you open your weather app and see that high amounts of rain are expected to fall in your area, it’s easy to conclude that the Brazos River Authority would increase the release from one of our reservoirs. But just like your checking the weather before heading out for the day, the BRA has to be prepared for predicted weather to change.
Though it’s understandable why some people would want the BRA to consider releasing water in advance if heavy rain is forecasted, in most cases, pre-releases could cause more problems, including contributing to flooding.
“We don’t include future rainfall forecasts as part of our operational procedures,” said Aaron Abel, BRA Water Services Manager. “We don’t know exactly how much it’s going to rain or where that rain will fall. Instead, we look at calculated inflows into the reservoir. These inflows, along with upstream flows that are measured at United States Geological Survey (USGS) gage locations and upstream reservoir releases, are what we base release decisions on. We do keep an eye out for potential rainfall to know what we could be expected, but the forecast does not determine our release rate.”
For example, sometimes widespread rain is predicted to fall upstream of a reservoir, but the precise location of where the rain will fall, and the total amount are unknown. Rainfall that was expected to fall upstream could move beyond the lake and fall heavily downstream. Or, an area may receive much less or much more rain than originally predicted. In this scenario, if the BRA had started pre-releasing water to lower the lake to accommodate additional rainfall and instead the storm moved further downstream, dropping rain on top of the newly released water, then the BRA’s pre-release would have made the flooding downstream much worse.
“You can look back to earlier this May, particularly in the central part of the basin near Lake Limestone,” Abel said. “Forecasted rainfall magnitudes over a short period of time, over a couple of days, showed eight to 10 inches of rainfall around Lake Limestone and downstream of the dam. At that time, we had some releases ongoing due to inflows coming into the reservoir from prior rain events. If we had seen that there was a lot of rain coming and increased the release prior to the actual rain, that immediately puts water downstream of the dam and causes river levels to become elevated. In that instance, we didn’t get eight to 10 inches of rain—we got three to five inches. That’s about half of what was originally forecasted. We would have been putting more water downstream for no reason.”
Another reason that the BRA Water Services team does not pre-release based on forecasted rainfall is to conserve water supply. If a pre-release was made and no rainfall followed, the reservoir level would be lowered and water supply storage would be lost. If a dry period follows and the lake is not refilled, the reservoir would not have the ability to fully provide water supply needed during dry periods for the cities, industry and agriculture that require water.
“When the BRA water supply reservoirs are full what comes into the reservoirs must go out,” Abel said. “This is done to maintain the lake levels safely and protect the integrity of our dams.”
These reservoirs are especially vital during periods of drought, when other sources of water may be limited.