FLOOD05064

• Designation Number: 205
• County: Larimer
• Community: Fort Collins
• Basin: South Platte
• Title: Master Drainageway Planning - Cooper Slough, Boxelder Creek, Fort Collins, Larimer County, Colorado
• Date: 8/1/1981
• Designation Date: 1/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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the channel crossings for the Colorado and Southern Railroad and Vine Drive.

An improved channel is requ,"red to convey t~e outflow downstream of State

Highway 14. Capacities of the detention facilities are limited to a maximum

storage volume of 200 acre-feet with surface areas less than 20 acres and

depth limited to 10 feet or less. The same improvements in reach 1 of

Boxelder Creek are proposed.

Figures 13 and 14 are schematics of the proposed improvements for

Alternative 2 and 3.

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Conceptual Designs

Conceptual designs based on the considerations presented earlier in this

section were completed for Alternatives 2 and 3 and the channel crossing

enlargements along Reaches 2 and 3 of Boxelder Creek. The results of the

design are to be used in estimating costs of the alternate improvements.

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Alternative 1

Alternative 1 considers no improvements to the existing drainage system.

Flood damage reduction is accomplished by floodplain zoning, restrictions to

encroachment or development, evacuation of the floodplain, flood proofing

individual structures or flood insurance. The costs associated with these

measures are generally not considered in this type of analysis and will not be

considered for this study.

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Alternative 2

Channelization and enlarged openings at channel crossings were considered

under Alternative 2. For channelization, grasslined, trapezoidal channels

with concrete trickle channel were designed for developed conditions to carry

the 10-, 50-, and 100-year peak flows for Cooper Slough. Alternatives 2a, 2b

and 2c refer to the 10-, 50-, and 100-year channel design frequencies, respec-

tively. Design velocities were limited to 5 fps. one foot of freeboard was

allowed. Side slopes of 5:1 were used to define the trapezoidal channel. A

peak flow of 2000 cfs is used for Reach 1 of Boxelder Creek above Prospect

Street. Downstream of Prospect Street the channel will remain in the natural

state because the area will be used as sludge applications for the City of

Fort Collins (reference 6). Proposed access roads paralleling the creek

should be built up to serve as berms and confine the flow. Due to limited

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