FLOOD01153

• County: Montezuma
• Community: Dolores
• Stream Name: Upper Dolores River
• Title: An Evaluation of the Dolores River at Dolores
• Date: 9/1/1992
• Prepared For: Dolores
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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ANALYSIS OF THE 100-YEAR FLOOD FOR
DOLORES RIVER AT DOLORES GAUGE

A backwater study for McPhee Reservoir was completed in July 1974 to estimate

the effect of the reservoir on the Town of Dolores. It was recommended that

the estimated lOO-year flood of 10,000 cfs be used to design flood dikes for

the Town of Dolores that would replace existing dikes and protect the town from

the backwater effects of the reservoir. A flood of 10,000 cfs is the maximum

flood of record that occurred in October 1911. A flood frequency analysis

using the log-Pearson Type III distribution indicated this historical flood had

a 100-year recurrence interval. The analysis used 58 ye~rs of annual maximum

recorded peak flo~s for the Dolores River at the Dolores gauge which was a

mixture of 55 snowmelt flood peaks and 3 rainfall flood pe~ks.

In September 1978,' the Corps of Engineers issued a flood hazard information

report for the Dolores River which estimated the 100-year flood at the Town of

Dolores to be 14,500 cfs. In their analysis, the r~in flood events were
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separated from the snowmelt events and a discharge-frequency curve was

developed for each type of event. A total of 61 snowmelt peaks and 42 rainfall

peaks were used. A curve was drawn by computing the composite probabilities
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using a formula recommended in the Water Resources Council guidelines,

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resulting in the estimate of 14,500 cfs.

Randy Peterson of the regional office recently completed a similar flood

frequency analysis for the Dolores River at Dolores that separated rainfall and

snowmelt flood peaks. His analysiS also estimated the 100-year flood to be

14,500 cfs, and is documented in bis memorandum of January 22, 1985 to the

Chief, Water ReSOurces Branch. We recommend that a peak v~lue of 14,500 ft3js

be considered as the IOO-year flood at the Dolores River at Dolores gauge.