FLOOD01297

• County: Clear Creek
• Community: Clear Creek County
• Stream Name: Clear Creek
• Title: Flood Insurance Study - Clear Creek County Unincorporated Areas
• Date: 6/1/1976
• Prepared For: US Department of Housing and Urban Development
• Prepared By: FIA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

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2.4 Flood Protection Measures

No flood protection measures are presently in effect in Clear
Creek County. The Public Service Company of Colorado maintains
a relatively large dam and reservoir at their Cabin Creek pumped
storage faci I ity south of the City. This dam regulates South
Clear Creek but its operating criteria are to release amounts
equal to inflow to the reservoir, thereby negating any possible
effects on flood flows. Georgetown Lake and other smal I water
supply and irrigation reservoirs have a very minimal effect on
flood peaks due to their smal I storage capacities and the fact
that they remain ful I or nearly so for the majority of the flood
season.

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ENGINEERING METHODS.

For streams studied within the County, standard hydrologic and
hydraulic study methods were used to determine the flood hazard
data required for this study. Floods having recurrence intervals
of 10, 50, 100, and 500 years have been selected as having special
significance for the land use and flood insurance program. The
analyses reported here reflect both current and planned conditions in
the watersheds of the streams.

3.1 Hydrologic Analysis

Hydrologic analyses were carried out to establ ish the peak
discharge-frequency relationships for floods of the selected
recurrence intervals for each stream studied within the County.

For each stream, flood-flow frequency data were based on a
regional hydrologic analyses set forth in a "Manual for Estimating
Flood Characteristics of Natural-Flow Streams in Colorado" (Reference
12). The method consists of a series of regression equations
from which flood characteristics can be estimated from measurable
physical and ci imatic parameters of drainage basins. Drainage area
and normal annual precipitation over that area are the two factors
required to estimate flood flows.

Results of the above described regional hydrologic analyses were
compared to statistical analyses of historical discharge records
at two gaging stations within Clear Creek County operated by the
U. S. Geological Survey (References 19, 20 & 23-25). Analysis of
these two stations fo.1 lowed the standard log-Pearson Type I I I method
as outlined by the Water Resources Counci I (Reference 26). Com-
parisons of Clear Creek at Lawson (29 years of record) and at Fal I
River (9 years of record) to results of the regional hydrologic
analysis showed a maximum difference in flood flows of 29 per cent
and an average difference of only 10 per cent. This error is

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