FLOOD01887

• Designation Number: 261
• County: Routt
• Community: Oak Creek
• Stream Name: Oak Creek
• Title: Flood Hazard Identification Report - Oak Creek, Colorado
• Date: 9/1/1986
• Designation Date: 11/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
,I

Hydraulic Analysis

An analysis of the hydraulic characteristics of Oak Creek was
performed in order to determine water surface elevations for the lOa-year
flood. Bridge elevations and sizes of openings were surveyed and
measured in the field on January 21 and 22, 1986. This data was combined
with cross-section data on Oak Creek taken from a~2' contour mapping of
the Town of Oak Creek (Ref. 3). This cross-section data became the input
data in the U.S. Army Corps of Engineers HEC-2 step-backwater computer
program.

The locations of the cross-sections are shown on the "Flooded Areas
Maps" (see Plates 3 to 13) and the hydraulic data for the cross-sections
is displayed in Table 1.

Roughness coefficients (Manning's "n" values) were also used as
HEC-2 input. Roughness values for Oak Creek varied from 0.035 for the
channel to 0.040 for the overbank areas.

Critical depth was the starting water surface elevation
location several hundred feet downstream from the study reach.
water surface elevations were reached within 3 cross-sections
cross-section 0.3, downstream from the study reach) as
calculations proceeded in the upstream direction.

at a
"True"
(i.e. by
computer

The computed lOa-year flood is outlined on the "Flooded Areas
Maps", plotted on the "Flood Profile" sheets, and tabulated in the
"Cross-section and Water Surface Elevation Data" table (Table 1).

A significant degree of overtopping would occur at each of the five
road crossings during a lOa-year flood event. Culvert capacities are
insufficient to pass the lOa-year flow in each case. Only minor blockage
of the culverts was assumed at each creek crossing. Insufficient culvert
capacity at the County Road 27 crossing would cause water to back up
south of the D & RG railroad tracks nearly to the Bell Ave. bridge
crossing of 'Oak Creek. Several low-lying residences would be flooded due
to this backwater effect. Insufficient capacity of the Bell Ave. and
Sharp Ave. crossings, in conjunction with adjacent low-lying ground to
the north of the creek would cause flooding to some of the buildings in
the downtown area. The baseball field area to the east of Moffat Ave.
would be flooded due to insufficient capacity of the Moffat Ave. crossing.

Flooded Areas

The areas covered by the lOa-year flood are shown on Plates 3
through 13 (Index given on Plate 2). Further information with regards to
flood elevations at various locations is given in the following sections
of this report. There is widespread flooding damage in the lOa-year
floodplain of Oak Creek.

6