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

flood probabilities up to about 1 percent. This is because available flood

records are usually for a short time period and further ~xtrapolations to

define floods with smaller probabilities are unreliable. Consequently, a

hydrometeorologic approach is generally employed to define an inflow design

hydrograph having a rare probability of exceedance and representing a reason-

able upper limit to expected flooding.

Inflow design hydrographs representing floods of specific or designated
frequency, can be developed from peak and volume frequency curves represent-
ing specified durations. When streamflow data are available at or near the
site, flood peak frequency curves are developed using statistical procedures
as outlined in the most recent edition of Hydrology Subcommittee, Interagency
Advisory Committee on Water Data Bulletin "Guidelines for Determining Flood
Flow Frequency.. When streamflow records are not avail ab le at or near the
site, peak discharge and volume frequency curves should be developed from
regional studies of stream gaging records for streams in the region.

In some cases, streamflow data may not be available for streams similar to the

one being evaluated. Consequently, it may be necessary to develop hydrographs

for specifiC frequencies using rainfall-frequency and rainfall-runoff relation-

Ships. Methods described in the previous paragraphs are more reliable and

should be used whenever adequate streamflow data are available.

An inflow design hydrograph developed to define the reasonable upper limit of

expected flooding is called the PMF (probable maximum flood). The PMF is

developed based upon the postulated occurrence of a storm producing PMP

(probable maximum precipitation), the maximum depth of precipitation that is

considered possible over the watershed. The PM? values are presented in a

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