FLOOD02366

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: The Big Thompson Flood of 1976 Field Trip Guidebook
• Date: 1/1/1976
• Prepared For: Annual meeting of Geological Society
• Prepared By: USGS
• Floodplain - Doc Type: Flood Documentation Report

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FLOOD HAZARD ESTIMATION FOR LAND USE PLANNING

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Prior to the Big Thompson Flood, little or no effective flood hazard

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planning had been done. It has been reported that only one resident of

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the canyon had flood insurance, and it is clear that few were even aware

of the hazards of flooding in the canyon. The Big Thompson drainage does

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not have a long history of habitation and therefore does not have a long

record of flooding. In 1938, a flash flood removed a short section of

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U. S. Highway 34. A peak discharge of 7600 c.f.s., the largest prior to

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this recent flood, was recorded in 1945. Failure of a small dam on a Big

Thompson tributary took three lives and several homes in 1951. Local

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residents have also reported a flood in 1965 which damaged roads and ruined

a mill. The next major drainage to the north, the Cache la Poudre River,

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has a longer record of habitation and more extensive documentation of floods.

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A major flood in 1864 caused Fort Collins to move to its present location.

Other noteworthy floods occurred in 1874, 1891 and 1904. Judging from des-

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criptions, two of these were of the same order of magnitude as the Big

Thompson Flood of 1976.

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Immediately following the Big Thompson Flood, the prevalent opinion ex-

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pressed by residents was that the canyon is not a suitable place for homes

and that the government should buy the land for recreational or other uses.

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However, in more recent months, hopes of such an arrangement have faded,

much of the evidence of the flood has been removed, a temporary road has

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been constructed and "for sale" signs are appearing in great numbers. The

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prevalent opinion now being expressed is that the July 31 event was a freak

storm and the popular myth is that it has a return period of 500 years. It

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appears that economic considerations have replaced the former preoccupation

with safety.

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