FLOOD04641

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Proposed Hydrology for use in Hydraulic Analysis of FEMA Flood Studies and Restudies
• Date: 9/1/1989
• Prepared For: State of Colorado
• Prepared By: Resource Consultants
• Floodplain - Doc Type: Educational/Technical/Reference Information

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TABLE .:L..l

SUMMARY OF CR PEAK DISClIARGES FROM PREVIOUS REPORTS

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All the basin parameters are presented in Table 3.2.
24-hour storm, rainfall depth for west Colorado
presented in Table 1. i WaS used.

For the
Springs

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REPORT

DRAINAGE AREA
muare mIles)

PEAK DISCHARGES illll
AT TIlE CONFLUENCE WITH CHEYENNE CREEK
10 YR 50 YR 100 YR 500 YR

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ESSW

1. 54

1,495

3.3

Hydrologic AnalysIs

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rn evaluating the hydrology for CR, the effort was made to
utilize the work done under the previous study as much as
possibl". The watershed subbasin boundaries and areas were
checked and found to be reasonable. The labeling of subbasins
shown in Figure 3.1. is exactly the same as for the ESSW except
for the elimInation of the leading number (all III In thIs
case).
Analysis of the other parameters developed by the previous
study were found to be unreliable for the case at hand; new
values for Tc' CN, and routIng parameters were derived. The
pri mary reason for this is that the previous values were based
on conditIons of full development throughout the basin which is
not the case at the current tIme. In additIon, a different
model (DABRO), which tended to generate higher CN values, was
used to perform the analysis.

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TAB!.!:; .l...l -=- 1!\JMMARY OF CR BASIN fARAMETERS

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DRAINAGE AREA CURVE NUMBER TIME OF
SUBBASIN ( square miles) CN CONCENTRATION . Ie
A-l 0.20 1.8 0.68
A-2 0.23 61 0.66
B-1 0.15 66 0.25
B-2 0.10 72 0.38
B-3 0.14 80 0.25
C-l 0.11 75 0.27
C-2 0.07 76 0.30
C-3 0.09 70 0.28
D-l 0.21 80 0.27
D-2 0.14 81 0.37
E 0.10 83 0.19

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Peak discharge results for the 24-hour AMC Ir storm at the
various points labeled on Figure 3.1 are tabulated in Table
3.3. At 1,520 cfs for the 100-year flood at the confluence of
Cheyenne Creek, this value is close to that established by the
ESSW. Given the dIfferences between the design storms and
m"thodologIes used under the two studIes, it Is not
unreasonable that the flow generated for existing conditions is

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R€~OURC€ CON~UlTI\NT~ INC

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