Big Thompson River

Big Thompson River
The headwaters of the Big Thompson River are in Rocky Mountain National Park.
Country	United States
State	Colorado
Major city	Loveland
Length	mi ( km) [1]
Discharge at	Loveland
- average	ft³/s ( m³/s) [2]
- maximum	ft³/s ( m³/s)
- minimum	ft³/s ( m³/s)
Source	Rocky Mountains
- coordinates	40°25′41″N 105°47′29″W / 40.42806, -105.79139 [3]
- elevation	ft ( m) [4]
Mouth	South Platte River
- location	Near Greeley
- coordinates	40°21′16″N 104°45′37″W / 40.35444, -104.76028 [3]
- elevation	ft ( m) [4]
Major tributaries
- left	North Fork Big Thompson River
- right	Little Thompson River
Big Thompson River highlighted in lower center of map.

The Big Thompson River is a tributary of the South Platte, approximately 78 miles (123 km) long, in the U.S. state of Colorado.

It rises in the Front Range of the Rocky Mountains, in Larimer County, Colorado, in Rocky Mountain National Park on the eastern slope of Longs Peak, near the town of Estes Park. It descends 1/2 mile (800 m) in elevation through the mountains in the spectacular 25 mi. (40 km) Big Thompson Canyon, emerging from the foothills west of Loveland.

It flows eastward south of Loveland across the plains into Weld County and joins the South Platte approximately 5 mi (8 km) south of Greeley. It receives the Little Thompson River approximately 4 mi (6 km) upstream from its mouth.

Water resources in the Big Thompson River are managed by the Northern Colorado Water Conservancy District as part of the Colorado-Big Thompson Project.

Big Thompson Canyon Flooding of 1976

On July 31, 1976, during the celebration of Colorado's centennial, the Big Thompson Canyon was the site of devastating flash floods that swept down the steep and narrow canyon, claiming the lives of 145 people, 6 of whom were never found. This flood was triggered by a nearly stationary thunderstorm near the upper section of the canyon that dumped 30 centimeters (12 inches) of rain in less than 4 hours (more than 3/4 of the annual rainfall for the area). Little rain fell over the lower section of the canyon, where many of the victims were. Around 9PM a wall of water more than 6 meters (20 ft) deep raced down the canyon at about 6 m/s (14 mph), destroying 400 cars, 418 houses and 52 businesses and washing out most of U.S. Route 34.

This flood was more than 4 times as strong as any in the 112-year record available in 1976, with a discharge of 1,000 cubic meters per second (30,000 ft³/s). However, paleoflood data obtained from radiocarbon dating of sediments indicates that such flooding occurs in the area every few thousand years.

Sources

D. Hyndman and D. Hyndman, Natural Hazards and Disasters (Thomson Brooks/Cole, 2006), 270-271.

See also

• List of Colorado rivers

References

External links

• I Dream of Genealogy Memorial for Big Thompson Canyon Flood Victims of 1976
• NOAA Site on the Big Thompson Canyon Floods

• Colorado State University: Big Thompson Watershed
• Northern Colorado Water Conservancy District
• Larimer County website: History of the flood

Colorado Big Thompson Project

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