FLOOD10388

• Designation Number: 596
• County: Adams
• Stream Name: Comanche Creek, Wolf Creek
• Basin: South Platte
• Title: Comanche Creek and Wolf Creek Floodplain Study
• Date: 5/1/2002
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SUMMARY

This report presents an analysis of the hydrologic and hydraulic factors influencing floodplains on Comanche
Creek and Wolf Creek in Adams County, Colorado. The analysis was limited to the 100-year storm event
along the study reaches except for, approximately, one mile along Comanche Creek, through the community of
Strasburg, where a detailed analysis was completed for the 10, 50 100 and 500-year storm events and a
floodway was calculated.

the water surface elevation
in Section 34, T3S, R62W,
created to make the floodway

of rise in
Creek
was

Adams County regulations define the floodway by allowing only 0.5 feet
The floodway was calculated for the 100-year flow only on Comanche
between Colorado Highway 36 and 26th A venue. A separate model
calculations in this reach of the Study Area.

Hydraulic Results

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mates for flood flows on Comanche Creek can
using unit hydrograph (CUHP) and routing
estimated by regression equations developed for

The results of the hydrologic analysis indicate that previous esti
be reduced by about forty percent. The flows estimated
(UDSWM2) computer models are consistent with peak flows
Colorado and the region

The limits of the 100-year floodplain for Comanche Creek are shown on Drawings CC-l through CC-9 and
Drawings WC-l through WC-5 show the 100-year floodplain for Wolf Creek. These drawings also show the
water surface profiles, cross-section locations, typical channel sections and the locations of crossing structures.
The hydraulic model files have been provided on a CD. The results of the hydraulic calculations are
summarized in Tables 7a and 7b, Floodplain Data and Floodplain and Floodway Data.

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made to reconcile the results of this study with the previous
replace the previous water surface profiles and floodplain

to the lack of documentation, no attempt was
It is intended that the results of this study will
in their entirety.

Due
PIS.
limits

The floodplain limits
channel and structure CvuUJLhJu,",

event
does
In

Flood Hazards

Several crossings will be overtopped on Comanche Creek and Wolf Creek during the 100-year flood event.
Overtopping of roadways will occur on Comanche Creek at; Comanche Road, 11th Avenue, 104th Avenue,
Headlight Road at 104th Avenue, 88th Avenue, 72nd Avenue, 64th Avenue, 56th Avenue, 26th Avenue,
Comanche Avenue and Defoe Street. Overtopping of roadwa6's will occur on Wolf Creek at Headlight Road,
Strasburg Road, 88th A venue, Piggot Road, 72nd A venue, 48t A venue, Wolf Creek Road and at 28t A venue
on Wolf Creek. A new bridge structure is under construction on Colorado Highway at Wolf Creek. This
structure was not analyzed for hydraulic capacity as part of this study.

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The analyses show that previous floodplain limits require significant modification The detailed study of
floodplains previously based on approximate hydraulic calculations and revisions to the flood flows caused
significant changes to the floodplain limits determined by the PIS. The analyses also show that proposed
future land use conditions will not have a measurable effect on floodplain limits. Flood hazards identified
include road over-toppings in several locations and several buildings along Comanche Creek are expected to be
effected by the 100-year flood.

Several buildings appear to be effected by 100-year flooding. These are located along Comanche Creek east of
Strasburg Road and north of 56th A venue and several residences near the intersection of 42nd Court and Defoe
Street may be effected by shallow flooding that results from overtopping of the main channel. Several
buildings between Colorado Highway 36 and 26th A venue east of Comanche A venue and west of Defoe Street
are also expected to be effected by flooding. Additional structures along Colorado Highway 36 between
Comanche Creek and Little Comanche Creek may also be susceptible to flooding.

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is located at

104th Ave.

Road and

A single residence in the northeasterly corner of the intersection of Headlight
the confluence of the Comanche Creek and Wolf Creek floodplains

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The majority of the reaches studied are in undeveloped portions of Adams County. Given the abundance of
available land and the risks associated with development in and around floodplains it is desirable to avoid
encroachment into the existing floodplains. However, selected reaches along the creeks have poorly defined
channels and some channel improvements or relocation may be a beneficial management approach. Any
development near a floodplain should consider the stability of the adjacent channel, channel banks and the
potential for erosion

No attempt was made to identify buildings within the floodplain that have been constructed since the taking of
the aerial photographs on April 28, 2002. The identification of structures above does not indicate that no other
structures will be effected by flooding. Each property owner should take steps to evaluate the risk of flooding
on their properties

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ndicates
occumng
No channel

to be relatively stable and the hydraulic analysis
ve. However, in selected reaches active erosion is
crossings where velocities will tend to be higher.

Much of the channel within the Study Area appears
that flood velocities would be generally non-eros
and continued erosion is expected, especially at
stability analyses were completed.

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McLaughlin Water Engineers
P:\20001A0-029\OO300\Final Aoodplain Report\Final Report.doc

7

Comanche Creek and Wolf Creek
Floodplain Study, May 2002

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