The image shared was one of oranges and reds, indicating Texans heading into the Memorial Day weekend were forecasted to receive five to seven inches of rain.
Thunderstorms and minor to moderate river flooding were expected across the state, but as we know now, it just didn’t happen that way.
The National Weather Service West Gulf River Forecast Center and other forecasters anticipated heavy rains to fall through the holiday weekend and to continue throughout that coming week, said Aaron Abel, Brazos River Authority water services manager.
While some rain did fall, it wasn’t near the amount originally anticipated, Abel said. The weather event serves as another reminder as to why the BRA does not release water from any of its three reservoirs based upon weather forecasts.
Using Memorial Day weekend as an example, had the BRA drawn down Possum Kingdom Lake one foot in anticipation of the storms, the amount of water supply released into the Brazos River would amount to about 17,000 to 18,000 acre-feet. An acre-foot is the amount of water needed to cover one acre – or 43,560 square feet or the size of a football field - with one foot of water. One acre-foot is equal to 325,851 gallons of water.
The storm ended up generating only about 1 to 2 inches of rain in the Possum Kingdom Lake area, Abel said. Fast forward to today, and the lake would be a foot low with little to no rain in the forecast to refill it, Abel said. Though recreationists would have noted the lake was a foot low, the real effect of that pre-release would have been that almost 6 billion gallons of water supply would have been sent downstream to potentially be lost to the Gulf of Mexico rather than being available in the Brazos River basin for homes, business, industry and oil production.
“If you don’t get significant rainfall and associated runoff you come out on the other side of that event one foot lower with no ability to refill that lost storage,” Abel said. “If you have a drought that starts at that time, that’s water that you’ve lost, and you can’t replenish. That’s water that could have been used to satisfy water supply demands, either lakeside or downstream.”
There is too much uncertainty in weather forecasts to base release decisions on them, especially in Texas.
Even if it had rained, predicting exactly where that rain falls is a whole new factor. Had the predicted rain for Memorial Day weekend fallen below the dam instead of on top of or upstream from the reservoir, a pre-release would have added water to the river downstream causing river levels to be higher than what would have occurred without a pre-release.
The additional rain and runoff on top of the water that was pre-released downstream along the Brazos River could create flood impacts that would not occur otherwise.
With these options in mind, determining when to open floodgates from BRA reservoirs is based on the science of hydrology, where streamflow is measured by United States Geological Survey, or USGS, gages placed throughout the basin. BRA hydrologists, along with professionals from the National Weather Service (NWS) Forecast Office in Fort Worth, the NWS-West Gulf River Forecast Center and the United States Army Corps of Engineers, work together to monitor streamflow at these gages as necessary to safely operate the reservoirs within the basin, maintain dam structures, and safeguard those living downstream of these reservoirs.
The Brazos River Authority water supply system includes 11 reservoirs. Eight of which are operated by the U.S. Army Corps of Engineers and are designed to temporarily store floodwaters, lessening the potential for flooding downstream. The BRA’s three reservoirs do not have flood storage capacity. So, when these reservoirs are full and additional water is flowing into the lakes, water must be released downstream to maintain safe water levels, or the dam structure could suffer damage or potential failure.
The National Weather Service West Gulf River Forecast Center, BRA and the Corps of Engineers work together in coordination with other agencies, such as the USGS, to manage water releases across the Brazos River basin.
Stretching from New Mexico to the Gulf of Mexico, the Brazos River watershed is a vital resource to individuals, households, businesses, industry, agriculture, mining and more.
Working to protect that resource is a continuous process for us all.