FLOOD11745

• Designation Number: 498
• County: Douglas
• Community: Parker
• Basin: South Platte
• Title: FIS - Parker
• Date: 3/2/1993
• Prepared For: Parker
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

Peak discharge-drainage area relationships for the streams studied
in detail, Cherry Creek, Sulphur Gulch, and Tallman Gulch, are
shown on Table 1.

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from the
sources studied were carried out to provide estimates of the
elevations of floods of the selected recurrence intervals.

For Sulphur and Tallman Gulches, the water-surface profiles for the
10-, 50-, 100-, and 500-year floods were developed using the SCS
WSP-2 computer program (Reference 15). These profiles and
elevations were compared with historic floods and the flood stages
then determined.

Water-surface profiles for floods along Cherry Creek were obtained
from the 1975 COE Floodplain Information report (Reference 12).

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The water-surface profiles for 10-, 50-, 100-, and SOD-year floods
on Cherry Creek were developed using the COE HEC-2 step-backwater
computer program (Reference 16). The computations were based on
channel and floodplain conditions as represented by survey data
gathered in April 1975 and as supplemented by later field
insvetigations.

Except for portions of Sulphur and Tallman Gulches, cross section
data were obtained by field measurements.

All bridges, culverts, and other structures were surveyed to obtain
elevation data and structural geometry.

Locations of selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1). For stream segments
for which a floodway was computed (Section 4.2), selected cross
section locations are also shown on the Flood Insurance Rate Map
(FIRM) (Exhibit 2).

Roughness coefficients (Manning's "n" were estimated by field
investigation and from pictures of the stream and its floodplain
using Rouahness Characteristics of Natural Channels (Reference 17),
Open-Channel Hvdraulics (Reference 18), and Handbook of Applied
Hvdraulics (Reference 19). The "n" values for Cherry Creek ranged
from 0.04 to 0.055 for the channel and from 0.061 to 0.095 for the
overbanks. For Sulphur and Tallman Gulches, the "n" values ranged
from 0.03 to 0.05 for the main channels and from 0.03 to 0.12 for
the overbanks.

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For Cherry Creek. the COE used critical depth to detrmine the
starting water-surface elevation. For Sulphur and Tallman Gulches,
the starting water-surface elevation was determined using the
stream slope at a starting valley cross section.

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