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

(6) Emergency evacuation. - Ungated spillways cannot be used to

evacuate a reservoir during emergencies. The capability of gated

spillways to draw down pools from the top of the gates to the

spillway crests can be an advantage when emergency evacuation to

reduce head on the dam is a concern.

(7) Economics and selection. - Designs to be evaluated should be

technically adequate alternatives. Economic considerations often

indicate whether to select either gated or ungated spillways. The

possibility of selecting a combination of more than one type of

spillway is also a consideration. Final selecti~n of the type of

crest control should be based on a comprehensive analysis of all

pertinent factors, including advantag..s, disadvantages, 1 imitations,

and feasibility of options.

c. Design considerations. - Dams and their appurtenant structures

should be designed to give satisfactory performance and to practically

eliminate the probability of failure. These guidelines identify

three specific classifications of spillways (service, auxiliary, and

emergency) and outlet works that are used to pass floodwaters, each

serving a particular function. The following paragraphs discuss

functional requirements.

Service spillways should be designed for frequent use and should safely

convey releases from a reservoir to the natural watercourse downstream

from the dam. Consideration must be given to waterway freeboard,

length of stilling basins, and amount of turbulence and other perform-

ance characteristics. It is acceptable for the crest structure,

waterway (e.g., chute, conduit, tunnel), and energy dissipator to

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