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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the SLA study were based on old DCM criteria.
peak rtlDoff for 6-hour and 24-hour storms
distribution.

They tabulated
with a type rrA

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The SLA work included detailed development of runoff parameters
but did not use specific channel routing. Although employing
TR-20 and subdividing the drainage into several subbasins,
their runoff model apparently used aggregate Tc and cumulative
basin area from the headwaters to the point of interest for
estimating peak discharge runoff. Therefore, time of
concentration and drainage area progressively increased for
points lower in the basin. In other words, subbasin areas and
time of concentrations were summed up outside the model and
input to TR-20 as a single basin to obtain discharge at a
specific point. The longest Tc was greater than 4.5 hours.
Accommodation of channel reach routing could only have been
Included as a function of the Tc calculation under this
approach.

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Results of the two previous studies are shown in Table 7.1.

TABLE 7. 1 .: SUMMARY OF SW PEAK DISCHARGES FROM PREVIOUS REPORTS

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DRAINAGE AREA

PEAK DISCHARGES ll.W
AT CONFLUENCE WITH SAND CREEK
10 YR 50 YR 100 YR 500 YR

REPORT

ml,!;!,li !!1)1e.~1

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FIS(l)
SLA

5.37

3,830

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Evaluat'i on of the SLA approach found it too coarse for
study. As only two subbasins had been used in modeling
well-developed watershed, new parameters were defined in
to get a more accurate representation of the hydrology.

this
this
order

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(1) Not tabulated In FIS as only an approximate study was done.

7.3 Hydrolo!;ic Analysis

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The basin was subdIvided into eleven subbasins as shown in
FIgure 7.1. HydrologIc parameters for these subbasins are
presentE!d in Table 7.2. The "general" case rainfall depth from
Table 1,1 was used for the 24-hour storm.

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R€~OURC€ CON~UlTI\NT~ INC

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