PERMFILE111290

• Permit No: M2000034
• IBM Index Class Name: Permit File
• Doc Date: 1/9/1984
• Doc Name: FLOOD INSURANCE STUDY
• Media Type: D
• Archive: No

FEB-07-1995 09:36
FROM ~ REGION 8 NTFtO TO ~ 913034939213 P. 07
damages Fran the flood were estimated at $602,000. The
estimated discharge from this flood was 22,000 cfs at Loveland,
larger than the 100-year discharge of 19,000 cfs (Reference 2).
The asst recent flood occurred on July 31, 1976, ns torrential
rains in the Big Thompson Canyon caused a severe flood, greater
than the 100-year flood. A total of 139 people lost their
lives. At Loveland, the flood and damage were less severe;
however, damages totaled as much as 5500,000 for some businesses
(Reference 7). The peak discharge at a gaging station located
at the mouth of the canyon was estimated at 31,000 cfs. At
Loveland, the peak discharge measured approximately 20,000 cfs,
approximately the same as the 1D0-year discharge (Reference 8).
2.4 Ftood Protection Measures
No flood protection structures exist on the Big Thompson River;
however, some protection is provided by weather reports and
local watches on stream gages during crucial storm periods
(Reference 2).
3.b EhGINEER7NG METHODS
For the flooding sources studied in detail in the community, standard
hydrologic and hydraulic study methods were used to determine the
flood hazard data required for this study. Ftood events at a magni-
tude which are expected to be equalled or exceeded once on the average
during any 10-, 50-, 100-, or 500-year period (recurrence intervals),
have been selected as having special significance for flood plain
management and for flood insurance premium rates_ These events,
commonly teru~ed the 10-, 50-, 100-, and 500-year floods,.have a 10,
2, 1, and 0.2 percent chance, respectively, of being equalled or
exceeded during arty year. Although the recurrence interval repre-
sents the long-term, avers a period between floods of a specific
magnitude, rare floods could occur at short intervals or even within
the same year. The risk of experiencing a rare flood increases when
periods greater than one year are considered. Fo•example. the risk
of having a flood which equals or exceeds the 1D0-Year flood (one
percent chance of annual occurrence) in any 50-year period is about
40 percent (4 in 10), and for arty 90-year period, the risk Increases
to about b0 percent (6 in 10). The analyses reported here reflect
flooding potentials based on conditions existing in the community at
. the time of completion of this study. Maps and flood elevations ::'il
be amended periodically to reflect future changes.
3.1 Hydrologic Analyses
i
I-(ydrologiC analyses were carried out to establish the peak
discharge-frequency relationships fpr floods of the selected
recurrence intervals for each flooding source studied in detail
affecting the community,

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