FLOOD03485

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Comparison of Estimated Flood Peaks with Historic Floods
• Date: 1/1/1986
• Prepared For: State of Colorado
• Prepared By: USDOI
• Floodplain - Doc Type: Educational/Technical/Reference Information

Table 2 sumrlarizes by percentage gro;Jplng the resuit~,; of cor:lparlS()r:~; O~ C I r-s::orciec LODe
peaks with estimated PMF peaks a1 var,ous Slles,

Table 2. - Numbers of recorded floOD peakS within ranges of per::;em of PMF peaKs

Range of percent of
PMF peak

Number of recorded
events

91-100
81-90
71-80
61-70
51-60
41-50
31-40
<30

2
7
4
9
8
13
8
10

GI

The current study is limited in scope to the comparison of peak flows, A similar study could be
performed for flood volumes, but the data base for large flood volumes is more limited than that
for peak flows, Although, many peak flows can be estimated by slope-area methods or by other
hydraulic techniques based on high water marks measured in areas without gauges, no such
techniques are available to estimate peak flood volumes without the presence of gauges in the
immediate vicinity, Yet, even where gauges do exist, they are ohen inundated by the very large
flows and provide no useful volumetric information during the highest levels of flooding,

CONCLUSIONS

The major conclusion drawn from this study is that the current data are plentiful and the methods
used by the USSR to prepare PMF estimates represent a technically reliable procedure that may
be used in different geographic areas. The PMF peaks produced using the USSR methodology are
generally close to the most extreme of the recorded rainflood peaks.
- ('I
J:;' /)
A second conclusion results from having found nine rainflood events that represent at least 80
percent of their associated estimated PMF peaks: extremely rare floods approaching PMF mag-
nitude have occurred and will continue to occur on very rare occasions throughout this country,

\
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A third conclusion is that similar studies should be repeated every 5 or 10 years, In general, the
years 1974 to 1984, were very wet throughout most of this country; they produced 13 of the
61 flood peaks listed in table 1, Additional wet cycles will occur in the future and produce new
peak flow data for use in updating and extending this work.

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