FLOOD00550

• County: Clear Creek
• Title: Engineering Division Technical Report Type 15 Flood Insurance Study Clear Creek County
• Date: 9/1/1990
• Prepared For: Clear Creek County
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Flood Documentation Report

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record from 1946 to 1986. The Golden gaging station was located . ~y.\~
approximately 21 miles downstream from the Lawson gage from 1911 VJ
to 1974 and from 1974 to present is located downstream Of, thp \.v:.,,(
Church Ditch. at ~
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HYDROLOGIC ANALYSIS "..;' ~ 1, ,~-.,oY'- ~.( "vi"\.'
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Methodolocrv y/-YJ.-v, (T\ott -I-~ ,.)7 (IV
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Discharge frequency relationships fOr Clear Creek were
based on a combined-population snowmelt~rainfall discharge
frequency analysis. This approach was taken)~ue to~e-basin'~
ex:t=ely__high-.elev:atian;.:....I!;OO feeL Lu1"ZC;-aOU=feet above mean -
sea . level. Rainfall discharge'--t'requency relationships were
estimated using the Environmental Protection Agency's (EPA)
storm Water Management Model (SWMM) as modified by the Missouri
River Division of the u..t. Army Corps of Engineers. Rainfall
runoff modeling was ~Jlected for developing the rainfall
discharge frequency relationship since infrequent rainfall
floods are not inherent in the Clear Creek streamflow records,
The snowmelt discharge frequency relationships were determined
from an intra-basin regional analysis. The regional analysis
was developed for Clear Creek by relating the drainage area to
the mean flood logari thIn and the standard deviation of the
~logarithms of the annual snowmelt peak discharges at two gaging
stations located on Clear Creek.

Rainfall Discharqe Freauencv

SWMM Model Confiauration

The Clear Creek basin was divided into 597 subcatchments,
which averaged 275 acres per subcatchment. Accumulated point
precipitation values at 30-minute, l-hour, 2-hour, 3-hour, and
6-hour time increments were obtained from the NOAA Atlas 2,
Volume III - Colorado (USDOC, 1973) for the 2-, 5-, 10-, 50-,
and 100-year flood frequencies. To better approximate the
values for rainfall events, the May to October series found in
NOAA Atlas 2 was used. The 500-year accumulated point
precipitation values were determined by extrapolating the 2-,
5-, 10-, 50-, and lOO-year values. Values for all frequencies
were adjusted for depth-area durations prior to application in
the SWMM. The maximum 6-hour point rainfall values and adjusted
rainfall values are presented in Table 2. Hypothetical storm
distribution for each frequency is listed in table 3.

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