The 7 Worst Flash Floods in Texas History

Everything is bigger in Texas, including the floods. A large part of Texas is called “flash flood alley.” This area includes the central part of the state and stretches all the way from Dallas to San Antonio. The soil is clay-like and rocky, so it doesn’t absorb water very well. The geography also makes it an especially risky location for flash floods. Storms hit the state from three sides: the Great Plains, the Gulf of Mexico, and the Pacific Ocean. Some areas are more prone to floods from storms, while others are more prone to flash floods.

What Is a Flash Flood?

Flash floods happen very fast. The National Weather Service defines it as flooding that happens quickly in an area that is normally dry or when water in a stream or creek rises very quickly above a predetermined flood level. An official flash flood has to occur six hours or less after an event like a storm, a dam breaking, or an ice jam breaking.

The Worst Flash Flood in Texas History

It’s hard to say exactly what makes a flood the absolute worst. Is it how much the water rose? How many people died? How many buildings were destroyed or damaged? The cost of the damage? There are many metrics to determine just how terrible a flood was.

1. The Highest Flash Flood in Texas History

On June 25, 1954, Hurricane Alice rolled into town after a record drought. The immense flooding was a one in 2,000 years event, meaning there is a 0.0005% chance of it happening in any year. The Rio Grande crested at 61.35 feet in Laredo, which is 10 feet higher than its previous flood crest. Over 16 inches of rain fell in 24 hours, leading to as much as 8 feet of floodwaters in towns like Eagle Pass and Ozona.

Perhaps the most damaging part of this storm was a flash flood in the small town of Ozona. A 30-foot-high flash flood described in some sources as a “wall of water” forced its way through a typically dry ravine and flooded the entire town, killing livestock and destroying the homes of 500 families.

Flooding also heavily affected the city of Laredo. It washed away the international bridge between Laredo and Nuevo Laredo, the city on the Mexican side of the border. It also damaged the water treatment plant so badly that it took nearly a week for the water service to resume.

2. The Deadliest Flash Flood in Texas History

On September 8th and 9th, 1921, a tropical depression made its way to San Antonio, Texas. The storm released 18 inches of rainfall onto the city. Just a few hours away in the small town of Thrall, over 38 inches of rain fell in 24 hours. That is the record for the most rain in 24 hours of any US storm.

Unfortunately, a huge 12-foot swell from the San Antonio River suddenly swept downtown in highly populated San Antonio, catching many by surprise. People rushed to upper floors of buildings and higher ground, but 51 people drowned in San Antonio alone. Across the whole state, over 200 people drowned in the flood waters.

As a result of this storm, city officials built a dam and bypass channel to help protect downtown San Antonio from future flooding.

3. The Most Buildings Damaged By a Flash Flood in Texas History

Hurricane Harvey is one of the most damaging storms ever in the U.S. It damaged over 204,000 homes in Texas, mostly due to a series of flash floods in the Houston area. Many homes were outside of the 100-year flood plain, so homeowners did not have flood insurance.

The storm was devastating and dangerous. Private citizens used their boats to rescue their neighbors and deliver supplies. The Houston Police also contributed to the rescue efforts. Their dive team rescued more than 3,000 people in the first four days after the storm. A group of five police officers rescued 40 people in 24 hours. In the entire Gulf Coast Area, the storm damaged over one million vehicles. About 800 wastewater treatment plants and 13 superfund sites flooded, spreading toxic waste.

The highest coastal storm surge of 12.5 feet caused flash flooding in a nature preserve and tons of damage in the town of Port Aransas. Nederland, just across the border from Louisiana, reported over 60 inches of rain, setting the record for the most rain in a single storm.

Houston’s dense population and geography created a dire situation. The county is 1,800 square miles, of which 70% was flooded with at least 18 inches of water. The city actually sank up to 2 centimeters due to the weight of the water, but it rebounded once the waters had receded.

The reason this storm had so many flash floods was that it stalled in one place for several days, dumping rain. Flooding in some areas of Texas, like Brazoria County, was due to breached levees.

4. The Most Expensive Flash Flood in Texas History

Hurricane Harvey is the most expensive storm in Texas history. It cost $125 billion dollars in damages overall. However, the most expensive flash flood event in Texas might be a recent storm that happened on August 22, 2022, in the Dallas-Fort Worth area. A storm dumped 15 inches of rain on the area in 24 hours. Almost 100 homes were damaged, which seems like peanuts compared to Hurricane Harvey. However, including damage to businesses and disruption to the supply chain, experts believe the cost of this storm will be as much as $6 billion dollars. This would be the most expensive flood in the state that was not related to a hurricane.

More Bad Floods in Texas History

Texas has had more than its fair share of floods. While there have been bigger floods since these ones came to pass, in their time, they were some of the worst floods to hit Texas up to that point.

5. 1913 Brazos River Flood

In December of 1913, the Brazos River spilled over its banks. It is one of Texas’ largest rivers and runs from the Gulf of Mexico to near Freeport. On December 11, 1913, it reached its highest crest of 56.4 feet. To this day the river has never flooded that high again. This came from a storm that happened between December 1st and 5th of that year. It dumped over 15 inches of rain in the area. It had already been a high rainfall year and the ground was already in a slightly flooded state. During this storm, the Colorado and Brazos Rivers actually merged briefly due to the flooding. 180 people drowned due to swift flood waters.

6. 1972 Flash Flood Disaster in South Central Texas

In 1972, 16 inches of rain fell across South Central Texas in just two hours. Flash floods from Blieders Creek and the Guadalupe and Comal Rivers inundated the small city of New Braunfels in minutes. 18 people drowned in the city. Other nearby cities of Seguin and San Marcos had no deaths but severe damage. The storm cost $20 million in damage, which would be over $140 million in damage today. Experts at the time predicted that quick warnings sent out by the Weather Service Offices in San Antonio and Austin saved many lives.

7. 2015 Texas–Oklahoma Flood and Tornado Outbreak

Following a week of heavy rains, a strong and slow storm settled over Texas and Oklahoma. Starting on May 24th, flash flood warnings were issued in Southeast Texas. Overnight, between May 25th and 26th, 11 inches of rain fell in the Houston area, resulting in more flash floods. The flooding caused a 25-square-foot sinkhole at the Dallas Fort Worth Airport. The Blanco River in Central Texas rose over 35 feet in a few hours. Overall, 14 people were confirmed dead in both Texas and Oklahoma, but more were listed as missing as they were never found.

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