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 43. summary of Cost Estimates for Alternative 3.

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Item Total Cost

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Channel Downstream of Highway 14,
Cooper Slough Reach 1

$ 498,800

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Pond at Highway 14

1,067,500

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Pond West of Cooper Slough

950,400

Pond at Colorado and Southern Railroad

958,400

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Channel Improvements, Reach 1
Boxelder Creek

1,340,900

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TOTAL COSTS

$4,717,000

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Annual Cost: 50-year life, 7-3/8 percent

$ 35B,000

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Operation and Maintenance

10,300

TOTAL ANNUAL COSTS

$ 368,300

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VIII. ECONOMIC ANALYSIS

An economic analysis to further evaluate the proposed alternative impro-

vements to alleviate flooding along the study reaches of Boxelder Creek and

Cooper Slough is based on the benefit-cost ratio of each alternative and net

benefits.

The cost of each alternative is based on the estimates presented in the

previous section. The benefits are the average annual flood damage reductions

derived from the alternative improvements and were found based on damage

discharge curves established for each reach. The damage discharge r.urves

present damage in dollars for existing conditions as a function of discharge.

The damage discharge curves are shown in Figures 15 and 16. The average

annual flood damage reduction of an alternative is the difference between the

damage of a given flow rate without improvements and the residual flood dama-

ges with improvements in place. The residual flood damage is the damage from

the damage discharge curve associated with the flow rate in excess of the

design discharge of the improvement.

Table 44 presents a summary of the economic analysis. It shows net bene-

fits (difference between average annual improvement cost and average annual

flood damage reductions) and benefit-cost ratio for each alternative by reach.

The results of the economic analysis show the ratios for the reaches range

between 0.2 and 3.7. The 0.2 is the benefit cost ratio for reach 1 of

Boxelder Creek. This is low because the floodplain is not presently deve-

loped. The benefit cost ratio for Cooper Slough reach 1 varies from about 1.3

to 3.7. For Alternatives 2a through 2c the benefit cost ratio is about 1.6

because larger channels are required since more water is entering the reach

than in Alternative 3 which shows a benefit cost ratio of 3.7. Reach 2 of

Cooper Slough shows benefit cost ratios from 3.2 to 3.6. The lowest ratio is

for Alternative 3 which ponds the water along reach 2 instead of using chan-

nels as in Alternative 2 to convey the water to reach 1.

Table 45 shows net benefits and benefit cost ratios for the entire study

area for Alternatives 2 and 3. The benefit cost ratios have a narrow range

between 2.1 and 2.7. Net benefits range between $363,000 and $546,000.

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