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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CWCB
CASEY

0.75
0.75

240

510

640
660

1,050

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basin in Monument. rn general, the watershed contains quite a
bIt of "pen space with natural vegetation.

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Soils throughout the basin are of
tend to be hIghly permeable.
classified as type "B" soils.

the loamy sand category and
They are hydrologically

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Two previous studies have been done on Crystal Creek. The
earlier of the two is the Casey's 85-87 Suhdivision 100-YR
Histori,~ Flood Plain (CASEY) (Reference 33). The most recent
study was done by the Colorado Water Conservation Board in
1986; it is titled the Elood Hazard Identification Report _
Crystal Creek and DIrty Woman Creek (CWCB) (Reference 34).

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14.2

Previous Studies

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The CWCB used the Colorado Urban Hydro graph Procedure (CUHP)
with a I-hour event of 1.90, 2.65, and 3.02-inch rainfall depth
for generating the 10-, 50-, and 100-year storms, respectively.
SCS soU type wi thin the watershed was assumed 50% "B" and 50%
"C" with development resulting in 15% of the basin area
impervious.

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The CASEY study utilized TR-20 modeling with a single basin
defined for the watershed. They used a design storm of 4.4
inch rainfall depth over a 24-hour duration with a Type IIA
distribution. Type "B" soils were assumed in their
determination of curve number.

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The peak discharge results of the two previous studies are
presentE!d in Table 14.1.

TABLE 14.1 cc SUMMARY OF CC PEAK DISCHARGES FROM PREVIOUS REPORTS

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REPORT

DRAINAGE AREA
muare miles)

PEAK DISCHARGES lfiil
WEST OF 12 ~ RG RR
10 YR 50 YR 100 YR 500 YR

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14.3

Hydrologic Analysis

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The total basin area used for this study is approximately the
same as for the two previous studies. It was divided into
three subbasins as shown on Figure 14.1. Subbasin 3 is
indicated with a dashed line because it does not contribute to
the flow along the study reach. It was included in order to
compare results with the previous studies. The assumed basin
parameters for input to the TR-20 model are listed in Table
14.2.

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61

R€~OURC€ CON~UlTI\NT~ INC

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