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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Table 23.

Alternative 2, Design Data for Conceptualized Channel
Crossings for Cooper Slough

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exit of culverts, riprap should be properly placed. During the final design

process, an erosion analysis should be made to determine any problem areas and

thoroughly evaluate potential erosion and sedimentation problems.

Location

Dimensions in
10 year

Feet for Design Recurrence Interval
50 Year 100 Year

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Alternative 3

Alternative 3 utilizes detention storage to reduce peak flows in the

Cooper Slough basin. The 100-year flood hydro graph for developed conditions

is the basis for sizing the detention ponds. Detention ponds at State Highway

14, Colorado and southern Railroad and at locations upstream of Vine Dri~e

were considered. A total volume of 205 acre-feet is necessary upstream of

Vine Drive. Specific sites upstream of Vine Drive were not sized due to the

lack of topographic data. The capacity of the detention facilities were

limited to a maximum of 200 acre-feet with surface area less than 20 acres.

Depth of water was limited to 10 feet or less. Table 25 presents a summary of

the design data for the detention ponds. The design data for the bridge data

and channel data for Boxelder Creek were already presented in Tables 24 and

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Vine Drive 4'x12' Box 2-4'x12' Box 3-4'xl0' Box
Colorado and Southern
Railroad 3-3'x8' Box 3-4'xl0' Box 4-4'xl0' Box
State Highway 14 6'x12' Box 3-6'xS' Box 3-6'x81 Box
Sherry Road 3-4'xl0' Box 4-6'x8 . Box 4-6'xl0' Box

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22.

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Design Flow Dimensions
Location (cfs) (in ft)
Private Drive 1 1200 2-6xlO Box
Private Drive 2 1200 2-6xl0 box
Prospect Street 2000 4-5xl0 Box
Lake Canal 1500 3-4xl0 Box
Larimer Weld Canal 3820 8-4x12 Box

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The capacity of the channel crossing at Colorado and Southern Railroad

and Vine Drive should be enlarged. Table 26 shows the design data for

culverts at these locations. An improved channel is required to convey the

outflow downstream of Highway 14.

To prevent erosion along the design channel, a maximum velocity of 5 fps

was allowed. To prevent scour at erosion control checks and the downstream

exit of culverts, riprap should be properly placed. During the final design

process, an erosion analysis should be made to determine any problem areas and

thoroughly evaluate potential erosion and sedimentation problems. The storage

volume for the detention facilities is for flood water only and does not

include sedimentation or required freeboard.

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Table 24. Alternatives 2 and 3, Design Data for Conceptualized
Channel Crossings for Boxelder Creek

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66

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