Flash Flood Alley: The Worst Floods in Central Texas History

There’s a stretch of Texas that runs from Dallas to San Antonio along Interstate 35, encompassing much of the state’s central core. It follows the curve of the Balcones Escarpment and reaches deep into the rugged terrain of the Texas Hill Country.

They call it Flash Flood Alley because, quite simply, it’s one of the most flood-prone areas in the entire world.

The combination of volatile weather patterns and the unique landscape of the Hill Country creates the perfect conditions for sudden, deadly flash flooding, similar to what we saw happen in Kerr County on July 4.

How Flash Flood Alley got its name

First of all, South-Central Texas is meteorologically primed for heavy rain. When a system of low atmospheric pressure stalls over the region, it can draw in deep moisture from the Gulf of Mexico. Monsoonal moisture from the Pacific Ocean, as well as weak cold fronts from the north all converge to produce exceptional rainfall over a short period.

The hilly terrain of the Balcones Escarpment provides extra vertical lift for air flow. When vertical motion in the atmosphere is maximized, rainfall rates increase, resulting in at least 4 inches of rain per hour at times.

The terrain does more than just enhance rainfall, it also funnels it down into the valleys. The region features dramatic elevation changes, with steep hills and valleys spread throughout.

Many of the valleys, such as the Guadalupe River valley, are also very narrow and winding. This accelerates the flow of water and causes rivers in the region to rise much faster than they would in flatter terrain.

Compounding the problem is the region’s topsoil. Thin layers of soil rest atop limestone or granite bedrock, which means very little water can soak into the ground. During intense rainfall events, most of the water becomes runoff, rushing straight into creeks and rivers. Such downpours can turn the waterways into raging torrents in a matter of minutes.

The worst floods ever in South-Central Texas

The Fourth of July weekend flooding across the Hill Country has become one of the worst flooding disasters to ever hit this part of the state. More than 100 people have died across the Hill Country, the majority of them along the Guadalupe River in Kerr County.

Radar estimates show up to 15 inches of rain fell across central and southern Kerr County. Even higher rainfall totals, up to 20 inches, were reported in parts of Travis, Williamson and Burnet counties, where several more deaths have been reported.

These are some of the worst floods on record to have hit the area:

September 1921: The remnants of a hurricane, which had made landfall on the east coast of Mexico, brought intense rainfall across South and Central Texas. Several rivers, such as the Guadalupe, San Antonio and San Gabriel rivers, were inundated with floodwaters.

An estimated 40 inches of rain fell near the small town of Thrall, northeast of Austin. The resulting floods killed 215 people, making it the deadliest flood in South-Central Texas history. The disaster also prompted the construction of flood control infrastructure in the region, including the Olmos Dam in San Antonio and, eventually, the famed San Antonio Riverwalk.

August 1978: The remnants of Tropical Storm Amelia produced devastating flooding across Central Texas and the Hill Country. The Medina River and its tributaries above Medina Lake were particularly hard-hit, along with the Guadalupe River system upstream from Canyon Lake.

Up to 48 inches of rain were recorded over two days in Medina, about 50 miles northwest of San Antonio, making it the wettest tropical cyclone on record in Texas — until Hurricane Harvey broke that record in 2017. Major flooding devastated Kendall, Kerr and Bandera counties, claiming 33 lives and causing damage worth more than $110 million, according to the U.S. Geological Survey.

July 1987: Major flooding hit the Guadalupe River on the morning of July 17, 1987. Slow-moving thunderstorms dumped 11 inches of rain near the headwaters of the Guadalupe in less than five hours. The result was very similar to what transpired in July 2025: a wall of water that traveled down the Guadalupe River through Ingram, Kerrville and Comfort.

The Guadalupe River at Kerrville crested at 37.72 feet, the second-highest crest ever recorded for that particular location. In Comfort, the river spilled two-thirds of a mile outside its normal banks.

Tragedy struck when a bus and van from the Pot O’ Gold Christian summer camp near Comfort were swept into the floodwaters. Of the 43 people caught in the current, 33 were rescued, but 10 teenagers lost their lives.

October 1998: Moisture from a pair of hurricanes in the eastern Pacific Ocean, as well as a stalled cold front, produced disastrous flash flooding along the Guadalupe River and over the San Antonio metro area

From Oct. 17-19, San Antonio picked up 15.61 inches of rain, including a record 13.35 inches in 24 hours. Even higher rainfall totals were recorded to the northeast, where more than 30 inches of rain fell in an area near San Marcos.

The San Antonio River crested at an unprecedented 64.2 feet in Elmendorf, in southern Bexar County. The flooding claimed 31 lives across the region.

July 2002: Six consecutive days of storms produced 40 to 45 inches of rainfall for parts of the Texas Hill Country. San Antonio was hit hardest on July 1, when the city recorded 9.52 inches of rain in a single day, the third-rainiest day in San Antonio weather history.

On July 4, water flowed over the Canyon Dam spillway for the first time since being completed in 1964, forcing the evacuation of thousands of residents along the Guadalupe River and in New Braunfels.

Floodwaters also approached the top of Medina Dam, prompting the evacuation of more communities downstream. The Medina River surged to 63.16 feet, more than 28 feet above flood stage.

In total, 12 people died during the 2002 floods, including four in San Antonio.