In Texas’ Flash Flood Alley, problems extend beyond terrain

May 28--Bridges failing, property destroyed, people missing.

Late this week Austinites once again awoke to the consequences of torrential rains.

Natural terrain in Central Texas -- steep-sloped creeks and thin soils mean little stops falling water from cascading down inundated soil -- carries much of the blame for earning the name Flash Flood Alley.

But to some degree, experts say, the devastation wrought by the floods is also the consequence of outdated road construction and the reluctance of some communities to bar construction in flood plains.

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Even as scientists predict harsher and more frequent floods, Central Texas communities are still wrestling with how much to regulate building in flood plains. Officials race to upgrade low water crossings as formerly rural, even frontierlike areas become suburban.

And beyond the very real miseries of moldy homes, lost belongings and washed-away lives, taxpayers are often on the hook.

Since the late 1970s, the federal government has paid out $54 million for flood claims in Austin and $43 million more in the rest of Travis County, the American-Statesman has found in an analysis of Federal Emergency Management Agency data.

Smaller communities devastated by floods have gotten hefty assistance. The federal government has paid out $18 million worth of claims in Wimberley, where homes were uprooted in 2015.

The problem is likely to get worse.

Increasing risk

In his 2008 book "Flash Floods in Texas," engineer Jonathan Burnett says the state "has some of the most flash flood-prone land in the world."

And such extreme floods are expected to become more frequent because of global warming, John Nielsen-Gammon, the state's climatologist and a Texas A&M University professor, told the American-Statesman in 2015.

"The rate of rainfall is limited by how much moisture the air can carry. The amount of moisture the air can carry is limited by its temperature. So the warmer the ocean and overlying atmosphere, the greater the amount of water that will be transported into Texas," he said. "If a region is vulnerable to flash flooding because of steep terrain, shallow soils and an increasingly built-up environment, the risk of flooding is going up."

As climate change causes extreme weather events to become more frequent and as areas of Travis and Hays counties downstream of the Hill Country continue to grow in population, both the severity of the flooding and the number of people in harm's way are expected to increase. The week before floods last year devastated northeastern San Marcos, the Census Bureau named it the fastest-growing city in the country for the third year in a row.

In many ways, these communities are trying to play catch-up as bigger populations face inundation.

Deadly crossings

Perhaps nowhere are they more exposed than at low water crossings, vestiges of a time when roads were little more than fords for wagons to cross oft-dry creeks.

Nowadays, about three-quarters of flooding deaths in Texas involve people in their cars.

Austin alone has about 400 low water crossings that sit below the 100-year flood plain, said Kevin Shunk, the city of Austin's flood plain administrator.

The city prioritizes flood mitigation improvement projects based on risk. Factors include the possible depth of water over a road and the velocity with which it could run, as well as vehicle traffic count on the road. Mitigation can include elevating a road and building bigger culverts beneath it, or even converting the low water crossing into a bridge.

Such projects can cost $1 million or more, Shunk said.

In 2010, city workers replaced Lakewood Drive's low water crossing through Bull Creek in West Austin with a bridge. Previously, the road basically ran along the creek's bottom.

"We don't do things that way anymore," Shunk said.

More recently, city workers upgraded a crossing of Slaughter Creek along David Moore Drive. But there remains a list of projects the city has eyed for flood mitigation, including work on Spicewood Springs and Old Spicewood Springs roads in northwestern Travis County and improvements to Old San Antonio Road in South Austin.

"There are more needs out there than we have funding to address," said Shunk, who said most of the city's upgrade money for low water crossings comes from the drainage utility fund.

Controlling urban runoff

City officials are looking at ways to update the city code to reduce storm runoff from developed properties.

Under city rules, new development may not increase the risk of flood damage on downstream properties. But many sites developed before detention requirements were introduced in the 1970s lack detention facilities of any kind, "and the runoff from these sites may currently contribute to downstream flooding," according to a city land-use report released in March.

Because flood plain regulations can affect property values, they have been a contentious issue in some communities.

The Statesman reported last year that San Marcos has been approving about a dozen projects per year in the 100-year flood plain -- the federally designated area where there is an estimated 1 percent chance of a major flood in any given year.

In October, after FEMA issued updated draft maps of the flood plain for parts of Hays County, the Wimberley City Council declined to adopt the maps, instead leaving it up to the property owners whether they will follow FEMA's guidelines.

Central Texans "have a history of development in places that are problematic," said Burnett, the engineer and author.

"It's our desire to be near the water -- we're such a dry state that we've always tried to put ourselves as close to the water as possible," he said. "We build houses overlooking a river: For 50 years that can be fine, and then overnight it can be a disaster."

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By the numbers

From 1978 to 2016, the Federal Emergency Management Agency has paid out more than $6.2 billion on about 204,000 flood insurance claims in Texas. Houston leads way with $1.4 billion in flood insurance claims. The Central Texas breakdown:

Travis County -- 917 claims worth $42.6 million

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Austin -- 2,053 claims worth $54.4 million in Austin

Hays County -- 351 claims worth $22.4 million

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San Marcos -- 659 claims worth $23.8 million

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Wimberley -- 138 claims for $18.4 million

Williamson County -- 205 claims worth nearly $8.7 million

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Round Rock -- 179 claims worth $5.4 million

Caldwell County--107 claims worth $ 5.7 million

Bastrop County -- 119 claims worth $4.5 million

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