July 31, 1976 Colorado

On July 31, 1976, a violent rainstorm hit the area where the Big Thompson Canyon is located. According to reports the rainfall was falling at an alarming rate of 2" per hour which caused the Big Thompson river to rise and return to its primordial state.

This all began when winds from the east pushed very humid air up the mountains. The unstable air continued rising as its water vapor condensed. The winds were less than 20 mph above 10,000 feet that was too weak to move the storm away. Humid high-altitude air combining with weak winds meant the storm pulled into little dry air to weaken the rainfall. Hardly any of the rain soaked into the steep-sided canyon. The river quickly went over its banks, filled with debris that acted like battering rams against downstream buildings and cars. The water then backed up in the canyon's narrow mouth, in floods, water often backs up as debris piles against bridges. The Floodwater sped up as it squeezed through narrow places was freed when the dam that was formed by debris burst loose.

Due to these events, occurring in such a short time the U.S. Army came to rescue 850 people off the tops of homes, canyon walls, and rocks. The flood destroyed 556 homes and 52 businesses. The total damage was $35.5 million to the area; it cost $1 million dollars to remove 320, 450 tons of debris. The storm and flood caused the Big Thompson River to change course in thirty places. The flood killed 144 people and it took the authorities working until mid-September to identify all the bodies. The town felt that most of the deaths occurred due to the lack of a timely warning.

To prevent this from happening again they installed a reverse 911 emergency system. This reverse system broadcasts phone calls to residents in danger areas and warns them at a rate of 1,000 plus calls per minute. Now the river has more room to spread out than in 1976; people were not allowed to rebuild in areas that floods are likely to scour. Highway signs in Big Thompson and other Colorado canyons are the flood's most apparent legacy. They read: "Climb to safety! In case of a flash flood."