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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MAJOR BASIN FEATURES

HYDROLOGIC INFORMATION

The Westerly Creek drainage basin is a crescent shaped basin draining flow toward
Sand Creek in a northerly direction. The basin upstream of Kelly Road Dam has
been described numerous times, most recently in the "Flood Hazard Area
Delineation, Westerly Creek" dated January, 1977 by Camp Dresser and McKee,
Inc. As this area is outside the limits of this study the reader is referred to the
aforementioned reference.

The Westerly Creek Drainage basin below Kelly Road Dam is fully developed with
primarily single family residential areas. The channel area is also largely
residential, however, large portions are apartment dwellings and commercial
areas. Flow generally begins on these residential lots and flows toward the street.
Streets generally flow toward Westerly Creek.

The basin between Kelly Road Dam and Stapleton International Airport is fully
urbanized with development ranging from small single family residences to
apartments and large shopping complexes. Development has encroached into the
floodplain along the entire study area and in some cases has obscured the entire
natural drainage channel. In these areas pipes were installed which had little
significant impact on the magnitude of the residual floodplain. The numerous
roadways crossing the channel have had a further impact on the floodplain.

The Westerly Creek basin studied in this report was divided into twenty-four sub-
basins. These sub-basins were analyzed using the Colorado Urban Hydrograph
Procedure Computer Program (CUHPB) developed by the Urban Drainage and
Flood Control District. Input values were derived from topographic mapping, the
Urban Storm Drainage Criteria Manual and Project Reuse Rainfall/Runoff
information. Important input and output parameters are tabulated in the table
entitled Drainage Basin Parameters (Table 1).

The improvements recently completed, or soon to be completed, have resulted in
some reduction of the floodplain and floodway. The improvements were designed
to convey the IO-year flood flows but in some places result in a reduction in the
area inundated by the IOO-year storm event.

Hydrographs generated by CUHPB were combined with the Kelly Road Dam

outflow hydrograph provided by the U.S. Army Corps of Engineers (USCOE) and

routed using the kinematic wave option of the USCOE HEC-I Flood Hydrograph

package computer program.

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