FLOOD06619

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Federal Guidelines for Selecting and Accommodating Inflow Design Floods for Dams
• Date: 2/1/1986
• Prepared For: State of Colorado
• Prepared By: FEMA
• Floodplain - Doc Type: Project

be apparent from an inspection of aerial photographs and top~graphic

maps that loss of life and extensive economic impacts attributable to

dam failure would occur and be unacceptable.

The hazard created by a dam is determined by comparing the impacts with

the dam failing to those from the same flood without dam failure. The

failure of a dam during a particular flood may increase the area flooded

and also alter the flow velocity, depth, and rate of rise which also

affect the amount of damages. To fully evaluate the hazard created by

a dam, a range of flood magnitudes and their probabilities needs to be

examined. The upper limit for this range is the PMF. When the PMF is

selected as the IOF, it is not necessary to make the comparative study

for a range of flood magnitudes, The comparative study is usually

needed for a range of flood magnitudes when an IOF less than the PMF is

contemp 1 ated.

Water surface profiles, flood wave trave1times, rates of rise, and
associated evacuation warning times should be determined for each
condition. Because computations of dambreaks and flood routings are
not precise, a conservative evaluation of the hazards should be made
based on confidence in the data. As noted previously, computations
should be carried only as far as necessary to reach a decision.

2. Selecting IOFs for Proposed Dams

Selecting an IOF for the hydrologic safety design of a dam requires

balancing the likelihood of failure by overtopping against the consequences

of dam failure. Consequences of failure include the loss of life and

social, environmental, and economic impacts. The i~ability to accurately

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