How Much Rain It Would Take to Fill the Highland Lakes

Photo by LCRA

The extreme drought lowered levels in Lake Travis, revealing formations not seen above water in some time.

A reader asked us this question today: as rain is falling and more is in the forecast, just how much would it take to get the Highland Lakes full again? Those lakes, Buchanan and Travis, are vital source of water for Central Texas, and are currently less than half full (or more than half empty, depending on your outlook).

The lakes neared historic lows during the drought last year, as massive amounts of water were sent to rice farmers downstream; as it got hotter and drier, more water evaporated out of the lakes than the City of Austin used in the entire year. So what would it take to get them back up?

“In order to fill Lake Travis, it’s going to take a really significant storm system, or series of storms,” Bob Rose, meteorologist for the Lower Colorado River Authority (LCRA), tells StateImpact Texas. “Because, you gotta remember, Lake Travis is 41 feet below full right now. So you’d have to generate a lot of water across the Hill Country to make this happen.” Lake Buchanan would be an easier fix, as that’s only 17 feet below average.

Rose says a storm system somewhere between fifteen to eighteen inches could completely fill the lake. But there’s no “magic number,” he says, because it depends on where exactly the heavy rain would fall.

“An individual rain storm like that would likely cause some catastrophic flooding,” Rose says. “Spread out over two or three storms would be much better.”

But a massive deluge like that wouldn’t be unprecedented. 

Rose remembers the Marble Falls “rain bomb” of 2007, where nineteen inches of rain fell during just eight hours, filling Lake Travis. And then there are the floods that ended the drought of record in the fifties, which caused even more damage in an already-suffering state. And let’s not forget Austin’s Memorial Day floods of 1981, which dumped up to11 inches of rain in three hours.

So it’s back to hoping for rain — just not too much of it all at once. The current forecast calls for between two to four inches, with isolated amounts up to six inches, from now until Friday evening in Central Texas. And even forlorn West Texas is getting in on the action with some much-needed rain.

Update: The LCRA said Friday morning that “Thursday’s overnight rains should result in a rise of about a foot or two on Lake Travis by the end of this weekend, while the elevation of Lake Buchanan should remain relatively unchanged.”