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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verifyIng the results from the ESSW, the PMCC used three
methods of analysis to generate hydrology; these were the
RatIonal Method, Colorado Urban lIydrograph Procedure (CUIIP),
and RatIonal Method by Computer. Although the Rational Method
resul ts were higher than those presented by the ESSW, the PMCC
ultimately used the ESSW values for their design work. The
peak discharge results of the outflow under Interstate 25 are
presented in Table 4.1 for the two studies.

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TABLE 4.1 :. SUMMARY OF SPR PEAK DISCHARGES FROM PREVIOUS REPORTS

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REPORT

DRAINAGE AREA
muari'. miles}.

PEAK DISCHARGES .Ldll
aI INTERSTATE 25
10 YR 50 YR 100 YR 500 YR

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ESSW
PMCC
-Rational Method
-CUHP
-Rational by
computer

3.72

1,523

3.72
3.72
3.72

1,779
1,531
1,785

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4.3

Hydrologic Analysis

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As with the CR basin, evaluation of the SprIng Run hydrology
utilized as much of the previous study work as was prudent.
With a few modi flcations, the watershed subbasin boundaries and
areas were defined the same as In the ESSW. The exceptIons
were subbasins 0 and K, which included small areas east of
Interstate 25. These eastern areas of the two subbasins have
been deleted as the Interstate forms the eastern boundary of
the watershed. Subbasin L-2 has not been included as recent
culvert upgrades drain off from this area to the south away
from SPR. The labeling of subbasins In FIgure 4.1 is the same
as for the ESSW, except for the elimination of the leading
number (all IV In tbis case).

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In order to obtain an accurate analysis for the hydrology in
the lower portions of the watershed, detailed representation of
the storage detention characteristics were included. Aside
from modeling storage routing through the Big Stratton
Reservoir, each of the three undeveloped ponding areas
downstream were also represented as separate storage detention
fad 11 tIes.

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The values used for T in the indIvidual subbasins were found
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to be reasonable and were used for this analysis. New values
for CN and routing parameters were determIned. The basin
parameters are shown in Table 4.2. For the 24-hour storm,
rainfall depth for west Colorado SprIngs from Table 1.1 was
used.

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20

R€~OURC€ CON~UlTI\NT~ INC

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