Floods in Colorado’s semi-arid climate? You bet. Fort Collins residents can testify to the inundation that occurred from more than fourteen inches of rain being dumped on their city in thirty-one hours in 1997. That is the amount typically received in a whole year. Floods perennially threaten much of the state because of the high topographic relief of the drainage basins, torrential spring thaws, and intense summer thunderstorms. Early pioneers often chose to build highways, railroads, and towns in canyons close to riverbanks. Predictably, flooding was among the first natural hazards of which new citizens became painfully aware. Large floods devastated Denver, Pueblo, and other Colorado cities in the early 1900’s.

Flooded campus at Colorado State University, Fort Collins Flood, July 28, 1997. Photo courtesy of Colorado State University

The most recent Colorado flood of September 2013 caused nine deaths and more than $2 billion in damages. An estimated 2,000 homes were damaged or destroyed statewide, and portions of roads and highways were washed away.

The Denver Post has a gallery of then-and-now photos of the September 2013 flood.

Colorado’s most expensive prior flood was probably the “Flood of 1965” in the South Platte River Basin south of Denver. This flood caused $508 million worth of damage and drowned six people. The losses can be attributed to the failure to realize the significance of the South Platte drainage routes and flood plains. Homes, shopping centers, and many other buildings occupied-and still occupy-land that has been intermittently flooded for many years.

Denver mobile home park near Bowles and Sante Fe, during theSouth Platte River flood of 1965. Photo by Duane Howell, Denver Post

Colorado’s greatest loss of life from flooding was caused by the Big Thompson Flood of July 31, 1976. This thousand-year flood was the result of a violent rainstorm that sent a wall of water down the canyon, causing the death of 144 residents and visitors. This flood may qualify as the worst natural disaster in the modern history of Colorado. The Climb to Safety signs that are now a common sight in Colorado’s canyons are a grim reminder of the power of nature and the fact that these geologic hazards are always present.

Home damaged during the Big Thompson Canyon Flood, July 31, 1976.