Flooding is the risk that’s all around us.

Nationwide, it is estimated that as many as 20% of American homes are at risk of flood-related damage and, on average, more than 80 people die each year in floods in the U.S., making this the second-most deadly weather event behind extreme heat.

Here in Colorado, that risk is particularly acute, due to the state’s unique geographical location and weather conditions that make it susceptible to flooding. Our state is dominated by deep ravines, steep mountain ranges and a number of narrow canyons. This makes the region more susceptible to floods, especially flash floods. Whenever there is heavy rainfall, the water funnels down through these canyons to the foothills of the mountains.

As of 2017, a total of 352 people have been killed by floods in Colorado. Here are the most destructive events to date.

The Big Thompson Flood

On July 31, 1976, thunderstorms upriver caused waters to rise in the Big Thompson Canyon in northern Colorado. Twelve to 14 inches of rain fell over the course of just four hours in the mountains, while down in the foothills, near the mouth of the canyon, the weather remained largely dry.

No one in the area had any idea of what was coming next.

Shortly after 9 pm that night a wall of water 20 feet high barreled down the canyon, destroying nearly everything in its path. In the end, the flood killed 144 people, five of whom were never found, and damaged 418 houses, 52 businesses and 400 cars.

The Big Thompson Flood, which still ranks as the worst flood in Colorado state history, was four times stronger than any other flood in the century before 1976.

The South Platte River Flood

It was the summer of 1965, and the Front Range was in the middle of a three-year long drought. So, when the rain started, nobody worried about it. It was a blessing to the dry land.

But the rain fell and fell, not stopping. On June 16, 1965 a total of 14 inches of rain fell over the course of four hours, building up in the South Platte River and swelling the river to 40 times its normal flow.

The dry land alongside the river—from Nebraska to Colorado—was devastated, swept clean by the 15-foot wall of water. Littleton, south of Denver, was most affected. The losses totaled more than $540 million (in 1965 dollars), and 21 people were killed.

The damage from this one flood led to much of the flood prevention measures and town planning that have shaped the modern Denver metro area.

The Pueblo Flood

Also known as “The Great Flood of Pueblo,” this flood started on June 3, 1921 after days of heavy rain. Due to this downpour, the Arkansas River flooded west of Pueblo, joined by Fountain Creek roughly 30 miles to the north of Pueblo.

These two waterways join right in the heart of downtown Pueblo, and that’s where the real damage happened. Waters that were estimated at the time to be as high as 15 meters swirled into the city, killing 78 people and causing more than $20 million in damage (shockingly, in 1921 dollars).

The Fort Collins Flood

Fort Collins sits at the base of the Front Range foothills, alongside the St Vrain River, one of the major waterways in northern Colorado. So, when heavy rains started to fall on July 28, 1997—at levels that broke several 100+-year-old records—the resulting flooding was devastating.

The usually tranquil Spring Creek overflowed into the city, wrecking dozens of businesses and killing five people. The resulting property and livestock damage totaled more than $250 million.

The 2013 Colorado Front Range Flood

For many current Front Range residents, this is “the big one.”

In September 2013, a slow moving cold front clashed with moist and humid monsoonal air coming from south of Colorado, stalling over the region and dumping rain for days. As a result, Boulder Creek overflowed its banks, inundating the city of Boulder as well as much of Boulder County to the east.

The rain was so heavy it broke all the records, reaching 17 inches on September 17, 2013. Boulder, in particular, broke its yearly record for rain prematurely with almost three more months remaining in the year. The flood killed 10 people, and forced the evacuation of roughly 11,000 local residents. More than 1,500 homes in the region were destroyed, and the damage to property amounted to $ 2 billion.

Protect yourself

Colorado is flood country. So, in the event of flooding, there are several steps that homeowners should take to minimize damage to their property.

  • Flood insurance: If you live in a flood plain, you simply must purchase flood insurance. Yes, it can be expensive, but in the event of a flood it just might save your finances.
  • Seal the house: Board up windows and doors so floodwaters can’t carry wreckage and debris into your house. Plastic sheets and rubber seals can be used to prevent water from seeping in through doors, and sandbags are useful in high water areas for the same reasons.
  • Stay informed: During the flood, listen to the radio, watch television and keep track of social media as possible for any warnings. If asked to evacuate, leave immediately, making sure to turn off all appliances—they can spark a fire in the event of a water-related power surge. Leave the premises immediately if any electrical outlets are submerged.