FLOOD07623

• Designation Number: 497
• County: Douglas
• Community: Parker
• Basin: South Platte
• Title: FIS - Parker
• Date: 7/1/1989
• Designation Date: 1/1/2000
• Floodplain - Doc Type: Floodplain Report/Masterplan

Peak discharge-drainage area relationships
in decail, Cherry Creek, Sulphur Gulch,
shown on Table 1.

for the streams studied
and Tallman Gulch, are

3.2 Hydraulic Analyses

i
Analyses of the hydraulic characteristics of flooding
sOllrces studied were carried out 'to provide estimates
elevati.ons, of floods of the selected: recurrence intervals.

f rom the
of the

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 histor:ic floods and the flood stages
then determined. '

The water-,surface profiles for 10-, :50-, 100-, and 500-year floods
on Cherry Creek were developed using the COE HEC-2 step-backwater
computer program (Reference 16). 'l,'he computations were based on
channel and floodplain condi t ions ~s represented by survey data
gathered ,in April 1975 and as ~upplemented by later field
. .. I
lnsvetlgatlons. '

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I
,
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Water-surface profiles for floods al:ong Cherry Creek were obtained
from the 1975 COE Floodplain InformaJ:ion report (Reference l2).

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

All bridges, culverts, and other str4ctures were surveyed to obtain
elevation data and structural geomet~y.
i
Locations of selected cross sectionsl used in the hydraulic analyses
are shown on the Flood Profiles (E~hibit 1). For stream segments
for which a floodway was computed I (Section 4.2), selected cross
section locations are also shown or) the Flood Insurance Rate Map
(FIRM) (Exhibit 2). '

Roughness coefficients (Manning's! "n" were estimated by field
investigation and from pictures of i the stream and its floodplain
using Roughness Characteristics of N~tural Channels (Reference 17),
Ooen"'Chartnel' Hvdraulics (Reference 118), and Handbook of Aoolied
Hvdraulics (Reference 19). The "n" i values for Cherry CreE\k rangE\d
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 chadnels and from 0.03 to 0.12 for
the overbanks.

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

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