Thursday, September 25, 2014

It Will Take an Insane Amount of Rain Before the Highland Lakes Recover | StateImpact Texas

Photo courtesy of the LCRA......Lake Travis is heading 
towards  its lowest levels in history if we have a dry fall.
Central Texas is having a pretty decent year, rain-wise. We’re sitting just below normal. And it’s been a good week, too: early Thursday, one part of Austin got over seven inches of rain.

So much rain fell over downtown Austin that the statue of Stevie Ray Vaughan along Lady Bird Lake looked like he was walking on water. It brought back memories of the Halloween floods last fall — back then Stevie was standing in water waist-deep. But these big rain events all have something in common: They really haven’t fallen where we need them most.

“The watershed that helps our water supplies isn’t here in Austin; it’s way up into the counties to the north of us. It’s the drainage that goes into Lakes Buchanan and Travis,” says John Hofmann, Executive Vice President of Water for the Lower Colorado River Authority (LCRA).

Hofmann says while the areas around the lakes got some decent rain earlier this summer, other than that it’s been pretty dry up there. So while Lake Austin is getting doused, the creekbeds that go into the Highland Lakes can stay relatively dry. Lake Travis has risen over a foot this week, and could go up another foot today. But it’s still nearly 40 feet below where it should be, and lower than it was a month ago.

And it’s not just where the water is falling that’s preventing the lakes from recovering. It’s the condition of the ground that it’s falling on.

If the ground is dry, it can soak that rain right up.

“You know, the water falls from rain. Some of it runs off into the reservoir, some of it recharges the groundwater. But a lot of it stays right near the surface. And it’s taken up by the plants. Or it just evaporates,” says Michael Young, an Associate Director at UT’s Bureau of Economic Geology.
“Even though 2014 so far has been near-normal precipitation or maybe a couple of inches behind,” Young says, “we’re getting no response from the reservoirs, and it’s because most of the water is soaking into the soil.”

Young is part of a team working on tools to better track soil moisture levels. He estimates that water lost from the soil could account for anywhere from 20 to 80 percent of the water losses during 2011, the driest year in Texas history.

“Outside of precipitation, [soil moisture] is one of the most important components of the water balance in this state,” Young says. “And we don’t know what that component is. It’s a complete black box across the state.”

Those water losses to dry soil continue today. “The first inch or two of rainfall in most of these events that we’ve had scattered around the summer are immediately soaked up by the soil,” says Hofmann with the LCRA. The rain this week has basically bought Central Texas a few weeks of water supply, he says.

All of this adds up to a struggling reservoir system for Central Texas. If you look at the water levels of Lake Travis over the years and graph them out, it’s almost like a heartbeat monitor. And starting in the mid-2000s, the lake looks likes it could use some life support.

If we have a dry fall, the Highland Lakes could reach their lowest levels by the end of December, and that would mean that from a reservoir standpoint, this drought is worse than the drought of record in the fifties.

So what would it take to bring the lakes back?

“A series of rain events that would result somewhere in the neighborhood of 15 to 20 inches of rainfall, widespread throughout that area, before we could see real meaningful improvement in our supplies,” says Hofmann with the LCRA.

There is a silver lining, however. Even though the lakes aren’t recovering yet, rainfall over the city still helps reduce the demands on them. It cools things down, reducing evaporation; it increases soil moisture, setting the stage for better runoffs next time it rains; and hopefully it keeps you from watering your lawn.

“We’re all optimistically watching the skies right now,” Hofmann says.
Mose Buchele contributed reporting.

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