When some residents of Wimberley woke up early Sunday morning to flooding inside their homes, the fear and surprise were palpable: The Texas Hill Country had been going through a record, multiyear drought.
But just three months earlier, local officials had voiced concerns about the rapidly growing region's vulnerability to devastating flooding.
“The more we know, the safer we will be when flooding occurs,” Hays County Judge Bert Cobb said in a February news release after county commissioners voted to help pay for an ongoing study by the Guadalupe-Blanco River Authority on flood risk for the area.
The region is one of the nation's most susceptible to such disasters, and a recent population explosion has made things even worse, with concrete replacing the soil and grass that once absorbed floodwaters. Hays County is the fifth-fastest-growing county in the country, and is home to San Marcos, the nation's fastest-growing city.
"They call this part of the world 'flash flood alley,'" Bill West, general manager of the river authority, said in an interview. "And the more rooftops you have on the watershed, the faster that runoff materializes down the river."
West added: "When the Blanco River used to rise, you had pastures out there, and ranchers had to get cattle out of the river bottom. Now you've got people at the river bottom."
The river authority's $3 million study, paid for in part by the federal and state governments, has been underway for years. But it is focused on predicting what could happen in a flood, not on major flood protection measures such as dams, which are lacking on the small rivers that run through the Hill Country.
Such big projects are unlikely in an age of cash-strapped local budgets and dwindling federal funds.
"The cost-benefit ratio associated with a physical structure is so hard to justify" for rare flooding events, West said.
It was the Blanco River whose record swelling this weekend wiped out hundreds of homes in Hays County and also proved deadly. The floods caused at least two deaths, and 13 other people swept away by the river remained unaccounted for Tuesday evening, said state Rep. Jason Isaac, R-Dripping Springs. Forecasters say more rain may fall in the area. The water that ballooned the Blanco River is now rushing down the Guadalupe River in South Texas, raising concerns downstream.
"It's just absolutely devastating," said Isaac, whose district was among the hardest hit. "The water was rising faster than at a level anybody had ever seen previously."
The name "flash flood alley" was born from the Hill Country's unique climate and terrain, the combination of which is a magnet for both severe storms and massive floods. The Balcones Escarpment, a geologic fault zone that borders the region, serves as a trap for warm, moist air coming in from the Gulf — or a meeting place for the Gulf air and the dry air from the west — causing some of the highest rainfall totals in the world. And that water can travel across the terrain at astonishing speed because of the Hill Country's thin soil and steep slopes.
But while Texas' bigger population centers tend to be along rivers with massive flood protection systems — Austin along the Colorado, Houston along the Brazos, Dallas and Fort Worth along the Trinity — few dams or lakes to capture floodwaters exist in the Hill Country's Guadalupe-Blanco river basin. The only one of note is Canyon Lake, which is along the Guadalupe before the Blanco and San Marcos rivers flow into it.
The lake was above its full capacity as of Tuesday evening, and the Guadalupe-Blanco River Authority, which operates it, is waiting to open the dam because of the flood conditions that already exist below it.
This is not the first time the Hill Country has suffered from massive flooding. The 2013 Halloween floods were the worst Austin had ever experienced and also caused significant damage in the surrounding area. And in October 1998, a storm dumped as much as 29 inches of rain in the region, killing 31 people and causing more than $750 million in estimated damages.
Now that the population of Hays County has increased more than 60 percent since then, West said education is an important tool, too. Many newcomers to the area have no idea of the flood risk to their homes, having only experienced drought for the past several years.
"This event's certainly going to help with that education process," he said.