FLOOD08560

• Designation Number: 228
• County: Denver
• Community: Denver
• Stream Name: Westerly Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Westerly Creek
• Date: 3/1/1983
• Designation Date: 1/1/1984
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Improvements to the Westerly Creek channel consist of constructing a 10-year
system comprised of box culvert and open channel segments. The box culvert
sizes range from 2 - 8' x 4' to 2 - 9' x 6'. Open channel reaches were typically 6 to
8 feet bottom width and 4:1 side slopes with a typical depth of 7 feet. The lower
3 feet are rip rap lined to protect against low flows with the remainder of the
channel grass lined.

D~ring the water surface profile computation, no blockage of culvert or
bridge was assumed and blockages of the waterway by houses and building
were treated in several different ways. In a reach (between two cross
sections used in the computation) where there are only a few houses or
buildings, the blockage effect was neglected. In a reach where houses or
buildings occupy a significant area of the water way, only the open area in
the cross section was considered effeetive for flow conveyance. Along the
reach between 11th Avenue and Montview Boulevard, the natural
Westerly Creek channel has been obliterated by development and
encroachment. The houses and buildings are so close together and so
regularly located along the reach between 11th Avenue and
Montview Boulevard, except the reaeh between 16th Avenue and
19th Avenue, that a row of houses or buildings within one street block was
treated as a bridge pier for the normal bridge routine in the backwater
computation. A representative cross section within a street block was used
as the average cross section of the block.

Roughness coefficients used in the hydraulic model were derived from previous
studies, field investigations and the construction drawings prepared for the

The average cross section was transferred with increase or decrease in
elevation to the four locations (two sections, one within and one outside the
bridge pier, downstream and upstream of the average cross section)
specified for the normal bridge routine computation in the HEC-2 computer
program. The street (perpendicular to the flow direction) between two
blocks was treated as an open channel between two bridges. Because the
natural drainage way between 16th Avenue and 19th Avenue is curved, cross
sections were also taken perpendicular to the natural drainage way, but at
shorter reaches than the reaches mentioned above. Also, as stated above,
only the open area in the cross section was considered effective for flow
conveyance.

improvements.

TABLE 3
ROUGHNESS COEFFICIENTS

Stapleton Airport, south boundary to Montview Blvd.
Montview Blvd. to East 14th Avenue

0.040
0.045

Improvements to the channel were inserted into the previously developed cross
sections in order to simulate the post-construction channel configuration. The
sections and locations remained consistent with the CDM report except where
additional sections were required to adequately model hydraulic conditions.

East 14th Avenue to East 12th Avenue

0.050
0.045
0.035
0.040
0.016

Results of the hydraulic analysis are tabulated and included herein (Table 4).

East 12th Avenue to Riehthofen Place

Richthofen Place to East 11th Avenue

Improved channel - grass lined

Concrete box culverts

HYDRAULIC ANALYSIS

As previously stated the CDM FHAD report served as the basis for this study. As

such the basic description of the analysis procedure from their study is ineluded as

follows:

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