FLOOD09485

• Designation Number: 206
• County: Larimer
• Community: Fort Collins
• Stream Name: Fossil Creek Drainage Basin
• Basin: South Platte
• Title: Master Drainageway Planning - Fossil Creek Drainage Basin, Fort Collins, Larimer County, Colorado
• Date: 8/1/1982
• Designation Date: 1/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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ECONOMIC ANALYSIS

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An economic analysis to further evaluate the alternative improvement

plans to alleviate ponding and roadway overtopping along Fossil Creek is based

on the benefit-cost ratio and net benefit of each alternative.

The cost of each alternative is based on the annual cost estimates pre-

sented in the previous section. The benefits, the average annual flood damage

reduction derived from the alternate improvements, were based on damage

discharge curves established for each reach. Damage discharge curves present

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

discharge curves for reaches 1, 2, 4 and 5 along Fossil Creek are shown in

Figu~es 33 and 34. Measurable flood damage along reach 3 was negligible. The

average annual flood damage reduction of an alternative is the difference bet-

ween the damage of a given flow rate without improvements and the residual

flood damages 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.

Table 35 presents a summary of the economic analysis. It shows annual

net costs (difference between annual improvement cost and average annual

benefits) and benefit-cost ratios for each reach and each alternative. The

results of the economic analysis show the benefit cost ratios to be less than

one for all alternative improvements along each reach. The range was from

0.04 for channelization along reach 4 to 0.85 for enlarging culverts along

reach 4. The benefit-cost ratios are low because the flood plains are narrow

except behind road embankments where ponding occurs. Also, there is little

development in the basin.

Table 36 shows a summary of net benefits and benefit-cost ratios for the

Fossil Creek study reach bY alternative. The benefit-cost ratios range from

0.08 to 0.43. Annual net costs range from $164,000 to $1,507,800.

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FIGURE 33.

DAMAGE DISCHARGE CURVES, FOSSIL CREEK
REACHES I AND 2

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20

18

16

14

12

10

8

6

4

2

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1000

2000

3000

4000

5000

DISCHARGE (cfs)