Flash Flood Alley is an area of

Central Texas Central Texas is a region in the U.S. state of Texas roughly bordered on the west by San Saba, to the southeast by Bryan- College Station, the south by San Marcos and to the north by Hillsboro. Central Texas overlaps with and includes part ...

that is considered the most

flash-flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash flo ...

prone region in the United States.

Location

Flash Flood Alley covers a crescent-shaped band along the

Balcones Escarpment The Balcones Fault or Balcones Fault Zone is an area of largely normal faulting Edwards Aquifer in the U.S. state of Texas that runs roughly from the southwest part of the state near Del Rio to the north-central region near Dallas along Inte ...

from west of

San Antonio San Antonio ( ; Spanish for " Saint Anthony") is a city in the U.S. state of Texas and the most populous city in Greater San Antonio. San Antonio is the third-largest metropolitan area in Texas and the 24th-largest metropolitan area in the ...

through

Austin Austin refers to: Common meanings * Austin, Texas, United States, a city * Austin (given name), a list of people and fictional characters * Austin (surname), a list of people and fictional characters * Austin Motor Company, a British car manufac ...

and

Waco Waco ( ) is a city in and the county seat of McLennan County, Texas, United States. It is situated along the Brazos River and I-35, halfway between Dallas and Austin. The city had a U.S. census estimated 2024 population of 146,608, making i ...

to the east of

Dallas Dallas () is a city in the U.S. state of Texas and the most populous city in the Dallas–Fort Worth metroplex, the List of Texas metropolitan areas, most populous metropolitan area in Texas and the Metropolitan statistical area, fourth-most ...

. The area includes the Guadalupe River and

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

basins. According to the

Guadalupe-Blanco River Authority The Guadalupe-Blanco River Authority or GBRA was formed in 1933 by the Texas legislature. Its main concerns are water supply and water Conservation ethic, conservation in the Guadalupe River (Texas), Guadalupe River Basin, which includes the Blanc ...

, the Guadalupe basin is "one of the three most dangerous regions in the country for flash floods".

Causes

The area experiences typical

flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...

ing in heavy rainstorms which often fill streets or lowlying areas and cause damage.

Flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...

s occur when the location of rain, heaviness of rain, and duration of rain combine to overload drainage streams and rivers in a very short time. The area is naturally prone to

flash flood A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and depressions. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, or tropical storm, or by meltwater from ice and snow. Flash f ...

s due to a combination of topography, geology, and climate. The issue is exacerbated by settlement patterns and development patterns in the region. The area has a

karst Karst () is a topography formed from the dissolution of soluble carbonate rocks such as limestone and Dolomite (rock), dolomite. It is characterized by features like poljes above and drainage systems with sinkholes and caves underground. Ther ...

terrain of worn limestone on steep hills and includes broad, shallow, normally slow-moving rivers that wind among the hills and into valleys. The area is semi-arid with rocky and shallow clay soils, which means soils don't soak up water but allows it to sheet off. When warm air from the Gulf hits the nearby Balcones Escarpment, it moves up the escarpments, condenses, and causes precipitation, which can pour down the hills quickly and fill streams and rivers. According to Texas State University geographer Richard Earl, "The region has some of the highest flood discharge per unit area of a drainage basin in the country". Storms move into the area from both the Pacific and the Gulf, and cooler air moves in from the

Great Plains The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

, causing an orographic effect. The moist, warm air from the Gulf and the Pacific meeting the cooler air from the north make intense rainfall a regular occurrence throughout the region. A similar effect can happen in cities with large amounts of paved land and outdated drainage systems, such as San Antonio, and can be exacerbated by

overgrazing Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature ...

in rural areas. Multiple populated areas in the region are situated along streambeds within flood plains between hills which act as a natural funnel. According to Earl, city planners have often allowed developers to build in ways that also exacerbate the issue in populated areas, such as by building in flood plains and not using

permeable paving Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques fo ...

materials. According to

CNN Cable News Network (CNN) is a multinational news organization operating, most notably, a website and a TV channel headquartered in Atlanta. Founded in 1980 by American media proprietor Ted Turner and Reese Schonfeld as a 24-hour cable ne ...

's reports on the 2025 floods,

global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

is making rainstorms deliver more rain, as a warmer atmosphere can hold more moisture. According to

Climate Central Climate Central is a nonprofit news organization that analyzes and reports on climate science. Composed of scientists and science journalists, the organization conducts scientific research on climate change and energy issues, and produces multime ...

, San Antonio rainfall intensity has increased by 6% since 1970 while Austin's has risen by 19%, meaning that more rain falls in a given hour than did decades ago.

Major floods

According to flood expert Hatim Sharif, a hydrologist and civil engineer at the

University of Texas at San Antonio The University of Texas at San Antonio (UTSA or UT San Antonio) is a Public university, public research university in San Antonio, Texas, United States. Established in 1969, According to Austin meteorologist Mary Wasson, in the period between 2011 and 2021 Texas experienced 500 flash floods.

1913

In December 1913 between 10 and 15 inches of rain fell in the greater area. 180 people died. Torrential rains fell across Central Texas starting the morning of 5 December, swelling the

Brazos River The Brazos River ( , ), called the ''Río de los Brazos de Dios'' (translated as "The River of the Arms of God") by early Spanish explorers, is the 14th-longest river in the United States at from its headwater source at the head of Blackwater ...

and causing it to shift course. The

overflowed its banks and joined the Brazos. The Brazos River and Valley Improvement Association formed in 1915 to address flooding issues. The first Lake Waco Dam was built in 1929. The Trinity River also flooded.

1921

In September 1921, a

Category 1 hurricane Category, plural categories, may refer to: General uses *Classification, the general act of allocating things to classes/categories Philosophy *Category of being * ''Categories'' (Aristotle) *Category (Kant) *Categories (Peirce) *Category (Vais ...

made landfall in Mexico and moved into Texas. According to the

U.S. Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on March ...

, from 8–10 September the San Antonio area received 7.38 inches of rain. 215 people died. San Antonio developed flood control plans, including the Olmos Dam and River Walk.

Thrall A thrall was a slave or Serfdom, serf in Scandinavia, Scandinavian lands during the Viking Age. The status of slave (, ) contrasts with that of the Franklin (class), freeman (, ) and the nobleman (, ). Etymology Thrall is from the Old Norse ...

received an estimated 40 inches of rain, Austin received 19, and San Antonio 15. The

Little Little is a synonym for small size and may refer to: Arts and entertainment * ''Little'' (album), 1990 debut album of Vic Chesnutt * ''Little'' (film), 2019 American comedy film *The Littles, a series of children's novels by American author John P ...

and San Gabriel Rivers also flooded.

1935

Near Uvalde, 22 inches of rain fell in under three hours.

1978

In July 1978, tropical storm Amelia made landfall and moved inland, stalling over the headwaters of the

Medina Medina, officially al-Madinah al-Munawwarah (, ), also known as Taybah () and known in pre-Islamic times as Yathrib (), is the capital of Medina Province (Saudi Arabia), Medina Province in the Hejaz region of western Kingdom of Saudi Arabia, ...

and Guadalupe Rivers. The Guadalupe crested at over 40 feet in Comfort. Thirty-three people drowned in the flooding.

1981

Shoal Creek flooded 24 May when a slow-moving storm settled over Austin. Thirteen people died.

1987

On July 17, 1987, a sudden flash flood swept a bus full of children away at a low water crossing and killed ten near

Comfort, Texas Comfort is an Unincorporated area, unincorporated community and census-designated place (CDP) in Kendall County, Texas, Kendall County, Texas, United States. As of the 2010 United States Census, 2010 census, it had a population of 2,363. Comfort ...

. On the night of July 16, and into the next morning, slow-moving storms dropped between 5 and 10 inches of rain, triggering immense flooding along the Guadalupe through Ingram,

Hunt Hunting is the Human activity, human practice of seeking, pursuing, capturing, and killing wildlife or feral animals. The most common reasons for humans to hunt are to obtain the animal's body for meat and useful animal products (fur/hide (sk ...

, Kerrvile, and Comfort. The Pot O' Gold camp was evacuating when a bus was swept away. In 1989, the story of the deaths and rescues was shown as the pilot episode of ''

Rescue 911 ''Rescue 911'' is an informational docudrama television series that premiered on CBS on April 18, 1989, and ended on August 27, 1996. The series was hosted by William Shatner and featured reenactments (and occasionally real footage) of emergenc ...

,'' and in 1993 was made into a television movie called '' The Flood: Who Will Save Our Children?'' The film followed the experiences of some of the children and their families, and starred

Joe Spano Joseph Peter Spano (born July 7, 1946) is an American actor known best for his roles as Lt. Henry Goldblume on ''Hill Street Blues'' and FBI Special Agent Tobias C. Fornell on '' NCIS''. He also voiced the Chuck E. Cheese (at the time Chuck E. ...

as Reverend Richard Koons.

1998

The remnants of Hurricane Madeline and Hurricane Lester flooded the San Jacinto, San Benard,

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, Lavaca, Guadalupe, and

Rivers in October 1998, killing 31. The city of San Antonio experienced a 500-year flood.

2002

The Guadalupe River flooded in July 2002 after the area received over of rain. Some parts of the area received a year's precipitation over a few days. 12 people died.

2007

In June, a slow-moving frontal system caused heavy rains. Marble Falls, one of the hardest hit areas, received 18 inches (460 mm) of rain in a period six hours. The headwaters of

Lake Marble Falls Lake Marble Falls is a reservoir on the Colorado River in the Texas Hill Country in the United States. The reservoir was formed in 1951 by the construction of Max Starcke Dam by the Lower Colorado River Authority. Originally named Marble Falls D ...

and

Lake Travis Lake Travis is a reservoir on the Colorado River in central Texas in the United States. It is named in honor of William B. Travis. Serving principally as a flood-control reservoir, Lake Travis' historical minimum to maximum water height cha ...

had 19 inches of rain totals recorded. Two people died.^{/sup>

2013

May

In May, the Olmos basin received over 17 inches of rain over the Memorial Day weekend, causing 2 deaths.

October

In October, in a 100-year flood

A 100-year flood, also called a 1% flood,Holmes, R.R., Jr., and Dinicola, K. (2010) ''100-Year flood–it's all about chance 'U.S. Geological Survey General Information Product 106/ref> is a flood event at a level that is reached or exceeded onc ...
, the Onion Creek rose to its highest levels since 1921, killing four.

2015

In a 100-year flood, the Blanco River rose 45 feet and caused 13 deaths and severe damage in Wimberley

Wimberley is a city in Hays County, Texas, United States. It is still predominantly a ranching area. The population was 2,839 at the 2020 census.
History

Wimberley started as a trading post settlement near Cypress Creek in 1848, the year Hay ...
over Memorial Day Weekend. The river had been at 5 feet at 9 pm on May 24, and by 1 am had reached 40 feet. Wimberley installed a monitoring system to send out cellphone alerts.

2018

In a 100-year flood, the Llano River

The Llano River ( ) is a tributary of the Colorado River, about long, in Texas in the United States. It drains part of the Edwards Plateau in Texas Hill Country northwest of Austin.

Two spring-fed tributaries, the North and South Llano, stret ...
washed out the Kingsland Bridge

Kingsland Bridge is a privately owned toll bridge, spanning the River Severn between Kingsland and Murivance in Shrewsbury, Shropshire, owned and operated by the Shrewsbury (Kingsland) Bridge Company. The toll point is located on the Murivance s ...
.

2025

June

In June, flash flooding in San Antonio killed 13 people. The area upstream had received over 7 inches of rain in three hours, which qualified as a 100-year event. It was the city's highest daily rainfall in over a decade and the 10th highest ever recorded.

On June 12, heavy rain began around 2 am. Within hours at least fifteen cars were swept off Loop 410 when Beitel Creek, which runs parallel to the road, flooded. At least eleven people were killed in the Beitel Creek area, with two others killed in nearby areas. According to the San Antonio River Authority, over 400 yards of the westbound access road lie within the 100-year-floodplain.

July

On July 4, four-months worth of rain fell within hours in and around the Texas Hill Country

The Texas Hill Country is a geographic region of Central and South Texas, forming the southeast part of the Edwards Plateau. Given its location, climate, terrain, and vegetation, the Hill Country can be considered the border between the Ame ...
, due to a mesoscale convective vortex
A mesovortex is a small-scale rotational feature found in a Thunderstorm, convective storm, such as a quasi-linear convective system (QLCS, i.e. squall line), a supercell, or the eyewall of a tropical cyclone. Mesovortices range in diameter from te ...
containing the remnant mid-level circulation of an Atlantic tropical storm, along with tropical east Pacific remnant moisture, resulting in over 135 deaths in the region (as of July 19, 2025), including many children attending Camp Mystic along the Guadalupe River.

At 4:00 a.m. the National Weather Service

The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
issued a particularly dangerous situation
A PDS tornado watch issued on December 14, 2022.
In weather forecasting in the United States, "particularly dangerous situation" (PDS) is the wording used by the National Weather Service and the Storm Prediction Center to convey special urgency in ...
warning for communities along the Guadalupe. In Hunt, Texas

Hunt is an unincorporated community in western Kerr County, Texas, United States. It is located in the heart of the Hill Country

The Texas Hill Country is a geographic region of Central and South Texas, forming the southeast part of th ...
, where the two branches of the Guadalupe River meet, the river gauge recorded a rise in 2 hours before failing when it reached . Downstream in Kerrville, the river surged to . Further downstream, in Comfort

Comfort is a state of physical or psychological ease, often characterized by the absence of hardship. Individuals experiencing a lack of comfort are typically described as uncomfortable or in discomfort. A degree of psychological comfort can b ...
, it surged to . The city of Kerrville issued a disaster declaration on 4 July following the floods. In total, of rain fell on some areas that experienced significant flood effects.

Flooding continued into Saturday, 5 July with two more flash flood emergencies being issued for areas around Lake Travis

Lake Travis is a reservoir on the Colorado River in central Texas in the United States. It is named in honor of William B. Travis.

Serving principally as a flood-control reservoir, Lake Travis' historical minimum to maximum water height cha ...
north of Austin. Later, a third flash flood emergency was issued for central Comal County

Comal County ( ) is a County (United States), county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 United States census, 2020 census, its population was 161,501. Comal County is known for its rich German-Texan and Eu ...
, noting that "local law enforcement reported flooding of the Guadalupe River". of rain fell northwest of Streeter.

See also

* List of flash floods

This list of notable flash floods summarizes the most widely reported events.

See also
* List of deadliest floods
* List of major dam failures
* 2021 European floods
References

{{Rivers, streams and springs

Flash
Flash

Flash, flas ...

* Hailstorm Alley

__NOTOC__
Hailstorm Alley is a colloquial term referring to an area of south and central Alberta, Canada where hail storms are frequently produced. These storms frequently produce hail that is damaging to property. This area stretches from High ...

* Tornado Alley

Tornado Alley, also known as Tornado Valley, is a loosely defined location of the central United States and, in the 21st century, Canada where tornadoes are most frequent. The term was first used in 1952 as the title of a research project to st ...

References

{{U.S. Belt regions, state=collapsed

Flood articles
Floods in Texas
Regions of the United States
Regions of Texas}