FLOOD04771

• County: Douglas
• Community: Parker
• Stream Name: Tallman Gulch Tributary No. 1
• Basin: South Platte
• Title: Flood Hazard Identification Report
• Date: 12/1/1986
• Prepared For: Parker
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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l!,ydraulic Analysis

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An analysis of the hydraulic characteristics of Tallman Gulch
Tributary No. 1 was performed in order to determine water surface
elevations for the 100-year flood. Several cross-sections were surveyed
in the field on January 9 and 10, 1986. This cross-section data was
combined with cross-section data on Tallman Gulch taken from a 2' contour
mapping of that stream and a cross-section from a flood report (Reference
2) by EHMG Engineers. This cross-section data became the input data in
the U.S. Army Corps of Engineers HEC-2 Step-backwater computer program.

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Other data used as HEC-2 input was bridge data for the Siebert
Circle bridge crossing of Tallman Gulch Tributary No.1, flow data (see
"Hydrologic Analysis" section of this report), and roughness coefficients
(Manning's "n" values). Roughness values for Tallman Gulch Tributary No.
1 varied from 0.035 to 0.050 for the channel and from 0.035 to 0.060 for
the overbank areas.

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The computed 100-year flood is outlined on the flooded areas maps,
plotted on the flood profile, and tabulated in the "Cross-section
Information" table (Table 1).

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Flooded Areas

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The areas covered by the loo-year flood are shown on Plate 2.
Further information with regards to flood elevations at various locations
is given in the following section of this report. There are currently no
buildings in the leO-year floodplain of Tallman Gulch Tributary No. 1.
It should be noted that the floodplain in the vicinity of Station 2+00 is
subject to change due to the presence of a headcut (sudden drop in
elevation due to erosion) at that location. The headcut is likely to
slowly move upstreecm with each major rainstorm.