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<br /> <br />CHJlPTER 1 <br /> <br />1HE BIG 1HOMPSON FLOOD <br /> <br />Flash floods are merciless destroyers. The incredible destructive power <br />and speed with which large volumes of water rush down mountain slopes and <br />across canyon floors make them killers. The Big Thompson flash flood <br />which struck on the evening of July 31, 1976, was no exception. A few <br />short hours separated the onset of heavy rain from the flood crest passing <br />the canyon mouth to quickly subside on the plains below. The heroic <br />efforts of law enforcement officers, who were in the canyon prior to <br />8:00 p.m.*, and rescue workers kept the loss of lives from being higher <br />but at least 135 persons were killed and the search for the missing continues <br />at the time of this report. <br /> <br />Big Thompson Canyon was an outdoorsman's paradise. One of many such scenic <br />spots in Colorado, it winds torturously down through the Front Range of the <br />Rocky Mountains a distance of some 25 miles (40 km). Estes Park marks the <br />western end of the canyon and it ends near Loveland where the mountains meet <br />the great plains. Dotted with several small communities, many year-round <br />homes, and mountain cabins, it had a permanent population of about 600 people <br />and attracted hundreds of overnight visitors each weekend to the cabins, <br />motels, campgrounds, and camper/trailer sites scattered along its entire <br />length. The total number of people in the canyon on the night of July 31 can <br />only be estimated. Larimer County officials place the number of people in <br />Big Thompson Canyon on that evening between 2,500 and 3,500. A great <br />majority of these were tourists, campers, climbers and other~ enjoying the <br />rugged beauty of the canyon. The canyon was easily accessible by good high-, <br />ways from both ends. Its eastern end at Loveland is 70 miles (113 km) from <br />Denver and 40 miles (64 km) from Boulder. Many out-of-state visitors as <br />well as Colorado residents were attracted to the canyon. U.S. Highway 34 <br />followed the river through the narrow canyon. The small river, usually a <br />clear, cold, rapidly flowing mountain stream 1 to 2 feet deep, descends <br />some 2,500 feet (760 m) through the 25-mile (40 km) long canyon. <br /> <br />The Big Thompson River is a tributary of the South Platte River. Its source <br />is in Rocky Mountain National Park in north-central Colorado. Its drainage <br />basin covers more than 800 square miles (2,070 sq. km). On the evening of <br />July 31, 1976, during the period 6:30 p.m. to about 11:00 p.m., very heavy <br />rain fell over a 70-square mile (180 sq. km) area in the central portion of <br />the watershed. The most intense rainfall, more than 12 inches (304 mm), <br />occurred over the slopes of the western third of the Big Thompson Canyon. <br />More than four inches of rain fell over the entire canyon area from near <br />Estes Park to Drake (see figure 1). The resulting runoff exceeded the <br />highest previously recorded by almost an order of magnitude, reaching an <br />estimated 31,200 cubic feet (880 cu. m) per second at the mouth of the <br /> <br />*Unless otherwise stated, all times given in this report are Mountain <br />Daylight Time. <br /> <br />1 <br />