The Brazos River Authority has several important relationships across the state, one of which is with the National Weather Service’s West Gulf River Forecast Center.
Stretching from New Mexico to the Gulf of America, the Brazos River watershed is a vital resource to individuals, households, businesses, industry, agriculture, mining, and more.
Whether it’s passing flood waters through a reservoir or releasing water to meet supply needs downstream, together the two agencies coordinate information and expertise to maximize efforts.
The National Weather Service has 13 river forecast centers across the country, and each of them handles hydrologic forecasts within the major river basins of their respective areas. The West Gulf River Forecast Center, WGRFC, handles 15 major rivers, including the Brazos River - essentially all rivers that empty into the western side of the Gulf – hence the name “West Gulf,” according to their website.
The WGRFC’s valuable expertise helps BRA hydrologists in planning, especially during times of heavy rainfall.
The BRA’s three reservoirs – lakes Possum Kingdom, Granbury, and Limestone - were built for water supply and have no flood control space. This means that when a lake is full, any additional water that enters the reservoir must be passed downstream to protect the structural integrity of the dam.
It’s a delicate balance: releasing enough water to prevent the dam from over-topping dam gates, but not so much that vital water supply is lost downstream.
“We rely on the West Gulf River Forecast Center’s modeling, expertise, and forecasting to provide us with information that helps us operate our reservoirs more effectively and safely,” said Chris Higgins, BRA lead hydrologist.
Higgins said the WGRFC provides the BRA with inflow forecasts (water anticipated to enter a lake) when there’s been heavy rainfall. This helps BRA hydrologists anticipate the possible magnitude and timing of an impending high flow event. While the two agencies communicate regularly, the WGRFC also provides the BRA hydrologists a means for quick data around the clock.
“They’ve set up a tool for us to be able to leverage their models in real-time,” Higgins said. “We can email this one account with certain information which will then trigger that program to run models and email us with that information.”
The WGRFC models include actual values and predicted weather forecasts.
And while the BRA doesn’t release water based on weather forecasts, knowing them helps everyone stay prepared to navigate through high-level rain events, Higgins said.
Higgins gave an example – Say weather forecasts are calling for heavy rainfall upstream of Possum Kingdom Lake. And part of that prediction includes anticipating the gauge upstream of PK to hit 30,000 cubic feet per second. With the lake already full, an inflow of that much might require the BRA to open three gates at Possum Kingdom Lake.
Since opening a gate at PK’s Morris Sheppard Dam takes about two hours, having that advance notice allows crews to “float” a gate. A floated status means the gate is unlocked. Going from unlocked to open takes about 30 to 45 minutes while opening a gate that is not floated could take several hours and occur during heavy rain conditions.
“These forecasts help us know, for instance, that a gate opening might be needed late in the evening. With this information, we can then coordinate with lake staff and let them know we’ll need to continue to keep a close eye on developing conditions during the after hours,” Higgins said. “We also give the Public Information Office a heads up that they may need to make changes to the website and social media alerting people to large flows moving downstream.”
The question many people ask is: If heavy rainfall is forecasted on the lake or upstream, why isn’t water released in advance of that storm?
Releasing in advance of a storm is not part of BRA operational protocol simply because weather prediction is a complex science, and forecasts are not always precise.
“If we were to prerelease, or release in anticipation of a weather event, and that rainfall event occurs 80 miles east of the lake, (it’s not uncommon for forecasted rainfall amounts and location to be off), then we’ve just evacuated water that could have otherwise been used to satisfy water supply demands, either lakeside or downstream,” Higgins said. “If we’re at the beginning of another drought, we’ve just compromised ourselves - that’s water that you’ve lost, and you can’t replenish. The other thing is, if we prerelease, we’re adding water to the river downstream. Then if rain events miss landing upstream and only occur downstream, we’ve exacerbated flooding.”
Another way the West Gulf River Forecast Center helps BRA hydrologists is by providing 15-day forecasts each week for parts of the basin, Higgins said. These forecasts help in operating the BRA’s System Operations Permit.
If there is available water in the basin that meet certain environmental flow requirements outlined in BRA’s water rights, that water can be diverted to meet additional water supply needs, Higgins said. However, to do that, the BRA hydrologists must inform the Texas Commission on Environmental Quality’s Brazos Watermaster ahead of time to access that water properly, he said. Having these forecasts helps the hydrologists in meeting everyone’s water supply needs more efficiently by allowing BRA to utilize the natural flow of the river to meet those needs under certain circumstances.
Any time the BRA hydrologists either increase or decrease a release rate at one of its three reservoirs, they will send that data to the WGRFC.
“The National Weather Service West Gulf River Forecast Center issues flood warnings to the public,” Higgins said. “Having the gate change information from our reservoirs helps them in their forecasts calculations, allowing them to provide even more accurate information to the public regarding potential high-flow hazards and flooding.”
The Brazos River Authority and the West Gulf River Forecast Center have a vital partnership, whether it’s water supply needs or flooding awareness, the sharing of expertise helps everyone in the Brazos basin.