WSP03196

• File Number: 8443.600
• Description: Narrows Unit - Studies
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 6/30/1975
• Author: Dames and Moore
• Title: Flood Study Narrows Dam South Platte River
• Water Supply Pro - Doc Type: Report/Study

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DAMES Iif. ~OAE
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The Element of Ri.sk

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 concern for protecti.on of the dam i.s 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 population'in the

Ft. Morgan area and downstreaui, Studies by the USBR estimate that

failure of the NarJ:ows DaTil \.;roul.u t esu.lt in flood elevations at Ft.

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Morgan that would be 4.2 feet higher than under natural conditions

without the dam and 7,5 f",et higher t:han if the dam would not fail.

If these estimates are comhined with the natural tendency of people

to occupy an area below a dam designed for flood control,' it is evident.

that -a tragically high loss of. Hfe,is pas.sible if-the dam is designed

to accept a risk of failure.

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Accord:f.r~gly, 'file recommend tJH.lt the Narrm.;s Dam be designed

to prevent failure of t,he dam, with no significnnt ri~jk being taken

of overtopping of the dhfil.

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