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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9.2

Previous Studies

Hydrology for the Frs was developed in the same manner as
outlined for the Sand Creek Main Stem (see section 8 of this
report). As with all the Sand Creek basins in this study,
hydrology for the SLA study was conducted as discussed under
previous studies for the Sand Creek West Fork. In this case,
Sl.A assumed a single drainage basin to represent Sand Creek
Central Fork. Results of the two previous studies are
presented in Table 9.1.

Two dIscharge values from SLA are presented in Table 9.1 for
comparative purposes. It Is interesting to note that the peak
discharge reduces between Platte Avenue and the confluence with
Sand Cr"ek East Fork. A possIble explanation for this is that
under dl~veloped conditlons the lower portion of the basin runs
off very quickly and does not contribute to the peak. Flow of
the upstream peak is then actually reduced as it is routed
through the natural channel to the basin outfall.

TABLE 9.1 -=- SUMMARY OF SC PEAK DISCHARGES FROM PREVIOUS REPORTS

REPORT

(1)

DRAINAGE AREA
.u;quare miles)

10 YR

PEAK DISCHARGES ~
50 YR 100 YR 500 YR

Frs
SLA

1. 8 (1)
1.24(2)
1. 97(1)

340

630

790
1,670
1,590

1,280

At the confluE,nce with Sand Creek East Fork.

(2)

At Platte Avenue.

9.3

lIydrolo~;ic AnalysIs

The current analysis maintaIned the same overall basin
boundaries as defined by SLA with the exception of a small area
north of the Chicago Rock Island and PacIfic Railroad. This
area has been diverted along the north right-of-way of the
railroad to discharge into Sand Creek Main Stem. Removal of
this area from the basin accounts for the slight discrepancy in
drainage area with the previous study.

The basin was divided into three subbasins and hydrologic
parameters were derived to reflect existing conditions. Values
of area, CN, and Tc used in modeling the hydrology are shown in
Table 9.2.

39

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