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

without the dam because of the potential for dam failure. There are
SIveral potential causes of dam failure, including hydrologic, geologic,
seismic, and structural. These guidel ines are 1 imited to selection of
the lOF for the hydrologic design of a dam to reduce the likelihood of
failure from a flood occurrence to an acceptable level.

Once a dam is constructed, the downstream hydrologic regime is perma-

nently changed and land use patterns are different from what they would

likely be without the dam. Consequently, for conditions with the dam

in place, evaluation of the impacts of dam failure should be based

upon both existing and prospective future develoment. Comparisons

between existing downstream conditions with and without the dam are not

relevant.

b. Determining area affected. - Key elements in determining the area

affected by a flood wave, resulting from a theoretical dam breach, are

the height of the flood wave and the length and width of river reach

over which it will persist. An associat~ item of concern is the flood

wave traveltime. These elements are functions of channel and flood

plain geometry, hydraulic head at the dam, vol\Jlle of stored water and

reservoir inflow, and the size, shape, and rate of dam breach. Special

cases where dam failure could tause domino-like failure of downstream

dams resulting in a cumulative flood wave large enough to cause a

hazard should also be considered. All of these factors should be

considered when delineating the area impacted by dam failure. The area

affected by potential flooding is defined from downstream flood pro-

files determined by hydraulic computational methods. Additional

guidance on inundation mapping may be found in "Emergency Action

s