FLOOD08812

• County: Morgan
• Community: Fort Morgan
• Stream Name: Narrows Dam
• Basin: South Platte
• Title: Flood Study Narrows Dam South Platte River
• Date: 6/1/1975
• Prepared For: CWCB
• Prepared By: Dames & Moore
• Floodplain - Doc Type: Floodplain Report/Masterplan

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DAMES 8 MOORE

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The Element of Risk

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Risks are involved in all aspects of human endeavor; including

transportation, health, building construction. Society makes decisions,

either directly or inadvertently, on the types and degrees of risks it <,

will take. It is appropriate, therefore, to talk in terms of risk in

the design of dams.

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There are two types of risks involved in dams. The first is

risk of failure of the main structure of the dam; the second is risk

of damage to the structure. These need to be considered separately,

because the first is concerned primarily with protection of human life;

the primary concern of the second is with economic optimization of

design.

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Risks of Dam Failure

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The Policy We Recommend

The primary design con0.ern, for protection of the dam is the

magnitude of the IDF and the risks that may be taken with respect to

loss of life in the event of dam failure.

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The South Platte Valley has significant populatj~on in the

Ft. Morgan area and downstream. Studies by the USER estimate that

failure of the Narrows Dam would result in flood elevati.ons at Ft.

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Morgan that would be 4.2 feet higher than under natural conditions

without the dam and 7.5 feet higher than if the dam would not fail.

If these estimates are combined with the fl8tural te,ndency of people

to occupy an area below a dam designed for fl~od control, it is evident

that a tragically high loss of Hfe is possible if the dam is designed

to accept a risk of failure.

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Accordingly, we recommend that the Narrows Dam be designed

to prevent failure of the d~m, with no significant risk being taken

of overtopping of the da;".

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