The Worst Flash Floods in U.S. History


Flash floods can occur quickly and without warning washing away everything in its path. A flash flood can occur when a dam breaks or a heavy thunderstorm many miles away drops copious amount of rain. There have been some terrible flash floods in history.


Flash floods are second to heat waves in weather related deaths in the United States, killing an average 100 Americans each year. There have been disastrous flash floods in the US but thankfully today, warning systems have lowered the death tolls.

The Great Flood of 1889 - Johnstown, Pennsylvania


The most famous flash flood and one of the all-time worse disasters in American history killed 2,200 people when the South Fork Dam 14 miles upstream from Johnstown collapsed. Johnstown had been built in a flood plain between the Stony Creek and Little Conemaugh rivers and had a population of 30,000. As the town grew, the riverbeds had become narrower.

The South Fork Dam held back Lake Conemaugh, which was actually on the side of a mountain 450 feet above Johnstown. There was always worry that the damn was in disrepair and would someday break, but it never did. After a night of heavy rains the damn finally broke at 4:07 PM the afternoon of May 31st. The flash flood lasted only 10 minutes with the water at times reaching 60 feet moving downhill at 40 mph.

After the flash flood, most blamed The South Fork Fishing and Hunting Club for the dam’s failure. The club had bought the lake and dam and supposedly repaired it. The club was a retreat for millionaires with members that included Andrew Mellon and Andrew Carnegie.

Johnstown was also hit with another flash flood on July 19, 1977 killing 76 people.

1889 Johnstown flood
1889 Johnstown flood

Rapid City, South Dakota – June 1972


Rapid City sits in the foothills of the Black Hills in South Dakota. During the night of June 9-10, in the Black Hills west of Rapid City, 10 inches of rain fell over a wide area with some areas getting as much as15” of rain in 6 hours.

Much of the rain that fell occurred below Pactola Reservoir, the main dam that protects Rapid City. Most of the flood waters flowed down Rapid Creek into the city. Water rushed through Rapid Creek at a rate of 50,000 cubic feet per second.

Debris flowing down Rapid Creek clogged the spillway of Canyon Creek Dam just to the west of Rapid City causing Canyon Creek dam to fail at 10:45 PM of the 9th, pouring more water into Rapid City. The flash flood in Rapid City and surrounding towns killed 238 people and injured 3,057.

Flood damage in Rapid City
1972 Rapid City flood

Big Thompson Canyon, Colorado – July 31, 1976


A holiday weekend with Colorado celebrating its 100th birthday and Big Thompson Canyon was crowded with campers. A popular camping, fishing and hiking spot, Big Thompson River runs along US Highway 34 down the east slope of the Rocky Mountains between Estes Park and Loveland, down a narrow canyon.

Near sunset on Saturday, July 31st, with around 3,000 campers in the canyon, thunderstorms started pouring rain at the headwaters of Big Thompson River in Rocky Mountain National Park

Thunderstorm in Big Thompson Canyon / Photo by John Asztalos


The thunderstorms were stationary for three hours at the top of the canyon. In two hours it rained 12” with 8” in just one hour. That is almost the yearly amount of precipitation for that area in just two hours.

The Big Thompson River, normally 2 feet high turned into a raging flash flood 19 feet high, roaring down the narrow canyon. State Patrol and local police raced up and down the highway warning residents and campers until US 34 was washed out, killing some of these troopers. In parts of the canyon, the flood waters were wall to wall. Halfway up the Big Thompson Canyon at Drake, Colorado, the river flow before the storm was 137 cubic feet per second. At 9 PM that Saturday night, the river flow was 31,200 cubic feet per second.

In two hours, the flash flood killed 144 people and five people were never found. During the flood, campers climbed up the steep canyon walls and others clung to pine trees and roof tops. Those who survived spent the night watching as others were swept down the river while propane tanks and cars exploded as they hit rocks.

That night from Denver, I watched the lightning from the storm over the same area for hours from just after dark until late night. The storm did not move.

US 34 washed out
U.S. 34 washed away in the canyon / photo by W.R. Hansen USGS

Arkansas – 2010


As campers slept in the Albert Pike Recreation Area of the Ouachita National Forest in southwestern Arkansas, heavy thunderstorms up stream of the Caddo and Little Missouri Rivers dumped 8 inches of rain in the area.

Just after midnight, the flash flood tore through the campgrounds. At 2 AM, the campground was under 4 feet of water and by 5 AM, the campground was submerged under 23 feet of water. 20 people were killed in the flash flood.

Other Notable Flash Floods


  • Man, West Virginia: The Buffalo Creek flash flood occurred on February 26, 1972 after three straight days of heavy rain caused an earthen dam to break. The dam held back 18 acres of coal mine drainage water. The dam broke at 8:10 that morning when many people were still asleep. The flash flood killed 125 people and destroyed the town of Saunders.

  • Cheyenne, Wyoming: August 1, 1985. Stationary thunderstorms over Cheyenne dropped 6 inches of rain in three hours plus huge amounts of hail causing a flash flood. 12 people were killed.

  • Heppner, Oregon: The deadliest natural disaster in Oregon history happened on June 14, 1903. Extremely heavy rain from a thunderstorm sent walls of flood waters down the normally peaceful Willow Creek killing more than 200 people.

  • Kansas City, Missouri: On October 4, 1998, a flash flood occurred after heavy thunderstorms in the city. 11 people were killed, 10 of them died in their cars.


Flash Flood Safety


There have been numerous other flash floods in the United States in rural areas and major cities and there will be more. There is a difference between a flood and a flash flood. A flash flood can happen in an instant and without any warning whereas a flood usually has some amount of forewarning. Please read Flash Flood Safety Rules and Tips for more.

Copyright © 2010 Sam Montana

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