FLOOD10854 ‎(2)‎

• Designation Number: 590
• County: Denver
• Community: Denver
• Title: FIS - Denver - Volume 1
• Date: 11/17/2005
• Prepared For: Denver
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Due to overbank split flows, a floodway along the South Platte River was not
delineated.

Water-surface elevations (WSELs) of floods of the selected recurrence intervals were
computed through the use of the USACE HEC-2 step-backwater computer program
(Reference 46).

A brief discussion of the hydraulic analysis of each stream stlldied by detailed....
methods follows:

Clear Creek

Cross-section data, Manning's "n" values, and starting water- surface elevations were
obtained from the 1979 UDFeD Flood Hazard Area Delineation report for
Clear Creek (Reference 22). Cross-section data for the HEC-2 analysis were
compiled from topographic mapping (Reference 47). Typical roughness or
Manning's "n" values used were 0.025 to 0.045 for the channel and 0.040 to 0.075
for the overbank areas.

Bear Creek

Cross-section data, Manning's "n" values, and starting WSELs were developed for
use in the 1979 UDFCD Flood Hazard Area Delineation report for Bear Creek
(Reference 48). Cross-section data were obtained photogrammetrically by digitizing
cross sections marked on aerial photographs of the stream channel and floodplain
(Reference 49). The digitized cross-section data were supplemented. with
cross sections taken from topographic mapping (Reference 50) developed from the
aerial photography. All bridge cross sections were obtained from actual field
measurements. Roughness coefficients for the channel and overbank areas were
estimated by field inspection of the study area. Manning's "n" values were 0.035 in
the channel and from 0.025 to 0.090 in the overbank areas.

Additional cross sections were included from channel improvement plans due to
recent grading and channel improvements in the vicinity of Lowell Boulevard.

Cherry Creek

Cross-section data, Manning's "n" values, and starting WSELs were obtained from
the 1976 UDFeD Flood Hazard Area Delineation report for Cherry Creek (Reference
10).

Revised cross sections reflecting recent channel improvements in the areas of
Bannock Street to First Avenue were obtained from the Wastewater Management
Division of the Denver Department of Public Works Cherry Creek channel
improvements reports (References 51 and 52).

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