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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REPORT

FIS
SlA

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8.3

TABLE 8.1- ,3UMMARY OF ,')11 PEAK DISCHARGES FROM PREVIOUS REPORTS

DRArNAGE AREA
llJrJare mIles)

PEAK DISCHARGES ~
AT CHICAGO ROCK ISlAND S. PACIFIC RR
10 YR 50 YR 100 YR 500 YR

16.3
16.3

1,640

3,470

4,450
8,520

6,870

Hydrologic Analysis

The SM drainage basin was subdivided into 47 subbasins in the
SlA study. This was considered a level of detail too fine for
floodplain mapping. Under the current analysis, the drainage
was subdivIded Into 15 subbasins keeping the maIn basin
boundary in tact. Runoff and routing parameters were developed
for existing conditions.

A slight discrepancy in contributing area was apparent along
Powers E,oulevard near Constitution Avenue and along the eastern
boundary of the drainage. These areas were assumed to be
noncontributing to the flow upstream of the railroad. This
accounts for the difference in total basin area between this
study and the previous study.

Runoff parameters of Area, eN, and Tc are presented in Table
8.2.

TABLE 8.2 .:. SUMMARY OF SM BASIN PARAMETERS

IlRAINAGE AREA CURVE NUMBER TIME OF
,')UBBASIN muare mUm CN CONCENTRATION . Ie
1 2.09 67 0.87
2 1.17 70 0.83
3 1.00 60 0.87
4 0.67 64 1.03
5 0.50 55 1.15
6 0.59 55 0.85
7 0.25 65 0.59
8 0.20 75 0.44
9 1. 75 55 1.47
10 0.77 65 0.75
11 0.65 75 0.86
12 0.56 75 0.86
13 0.69 78 0.81
14 1.89 87 0.65
15 2.22 85 0.65

Peak discharge results at the hydrologic discharge points
indicated on Figure 8.1 are shown in Table 8.3 for the 24-hour
AMC II storm. The 100-year flow of 7,880 cfs at the Chicago
Rock Island and Pacific Railroad is lower than the 8,520 cfs
obtained by SLA. As SLA assumed full development, one might

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R€~OURC€ CON~ULTI\NT~ INC