Why Did Waters Rise So Quickly in the Texas Flash Floods?
Flash floods happen when heavy rains unleash more water than the ground can absorb, causing that water to pile up and flow to low-lying areas
Two women survey the damage caused by flash flooding on the bank Guadalupe River on July 5, 2025, in Center Point, Texas. Heavy rainfall caused flooding along the Guadalupe River in central Texas with multiple fatalities reported.
Jim Vondruska/Getty Images
In the wee hours of Friday morning, the Guadalupe River in Texas Hill Country rose 26 feet in just 45 minutes. Like all flash floods, this record-breaking water swell resulted from a large amount of rain that drenched one area over a relatively short amount of time. Flash floods are so named because waters can rise extremely quickly—within minutes to hours of when rains begin—catching people unaware, as happened in Texas on July 4. At least 82 people died in those floods.
The devastating event in Texas happened because of a convergence of ingredients. Flash floods can happen when a storm lingers over an area for a period of time and when a storm has extremely high rainfall rates. In the recent event in Texas, there was a small area along the south fork of the Guadalupe Riverwhere six to 10 inches of rain fell in just three hours—a stunning amount of precipitation.
And in intense rainfalls, the ground simply cannot absorb water as quickly as it comes down. This is particularly the case in urban areas, where paved surfaces are more impervious to water than soil, grblock or other natural ground cover are. The ground is also less able to soak up water if it is already saturated from previous rains or if there has been an intense drought that has hardened soils.
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Because the ground cannot soak up the water, it piles up on the surface, starting in the lowest-lying areas. In Texas, all that water piled up in the Guadalupe River bed, as the river had very low water levels prior to the event. The storm producing those high rains was also moving along the flow of the river, which produces higher river levels than storms moving against the flow, according to research cited by retired National Weather Service meteorologist Alan Gerard on his blog. River gauges show the Guadalupe River at one point rose from 7.7 feet of water with a flow of 8 cubic feet per second when the storm started just after 1 a.m., to more than 29 feet with a flow of 120,000 cubic feet per second by 4:30 a.m., Gerard wrote. The onslaught of water can mean a stream or river overtops its banks, flooding nearby areas.
Flash floods can be so damaging because water is incredibly powerful. Even six inches of quickly moving water can knock a person off their feet, and two feet of water can float a car. The faster the water is moving, the greater the force it exerts on a car, person or structure—that pressure increases by the square of the water’s velocity.
