More Than 38,000 Residential Structures Were Within the Texas Flood Zone Known as ‘Flash Flood Alley’

At least 38,600 residential structures were within the flood zone during the July 4 Texas floods, where heavy rainfall caused rivers to swell and created flash flooding.

Those structures were within the flood footprint of counties deemed eligible for individual and public assistance by the Federal Emergency Management Agency, according to an analysis by Cotality Hazard HQ Command Central.

The report revealed Tom Green (10,837), Travis (8,671), Williamson (4,976), and Burnet (3,926) counties had the greatest number of residential properties potentially impacted by flooding.

The Cotality analysis also identified Kerr County with at least 5,939 properties with the potential to be impacted by flooding, but not all the structures within the flood footprint were damaged.

The analysis considered first-floor height elevation and any residential property with as little as one inch of water, which was considered impacted.

Camp Mystic is located in Kerr County, near the town of Hunt. The camp is along the banks of the Guadalupe River—which, at the height of the flooding, rose 26 feet in just 45 minutes, according to state officials.

Hill Country

Hill Country in Central Texas is where the Guadalupe River is located.

This area of the state, known as “flash flood alley,” is the corridor along the Balcones Escarpment—an area of steep limestone hills with thin soil and urbanized corridors that quickly move rainwater into rivers, says Cotality.

This “alley” stretches from San Antonio through Austin to Dallas. The report says it’s common to have flash floods in this area because of the combination of the terrain and the Gulf-fed storms with heavy, prolonged rainfall.

The Texas Parks & Wildlife Department explains parts of Hill Country sit on the Edwards Plateau—high, flat land that, over many millions of years, has been eroded into hilly terrain. It also has springs, steep canyons, and underground lakes in the Edwards Aquifer (an underground layer of rock or sand that captures and holds water).

Cotality’s analysis says the rainfall event that caused the flash floods is traced to a “convective vortex that formed when lingering Gulf moisture from Tropical storm Barry stalled over the Hill Country.” This slow-moving storm brought rainfall rates that topped 3 inches per hour, “creating an explosive rise in the Guadalupe River,” according to the report.

Cleanup and rebuilding

The loss of life has devastated the tiny Texas communities. Officials say the overall death toll has risen past 130 people. In addition, the cleanup and rebuilding process is expected to be a challenge. Accuweather preliminary estimates $18 billion to $22 billion in total damage and economic loss.

The July flooding brought to the forefront the insurance gap among Texans, as industry experts say most Texas residents don’t have flood insurance.

“We’re really underinsured when it comes to flooding,” says Rich Johnson, spokesperson for the Insurance Council of Texas, a trade group representing many insurers in the state, told the NBC affiliate in Dallas.

“The average, statewide, is only 7% of homes have flood insurance. When you get inland, like the Dallas-Fort Worth area, San Antonio, and where these floods took place in Hunt, it’s 1% or 2% of people have flood insurance,” says Johnson.

Meanwhile, FEMA included Camp Mystic in a “special flood hazard area” in its National Flood Insurance map for Kerr County in 2011, according to a review by The Associated Press. However, federal regulators repeatedly granted appeals to remove Camp Mystic buildings from their 100-year flood map.

That designation means an area is likely to be flooded during a 100-year flood—so severe that it has only a 1% chance of happening in any given year, according the the AP.

Texas Gov. Greg Abbott announced that qualifying Texans in the following counties are eligible for FEMA’s Individual Assistance program: Burnet, Kerr, San Saba, Tom Green, Travis, and Williamson.

Texans can apply for FEMA disaster assistance online at disasterassistance.gov or by calling 800-621-3362.