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

I

I

XI. PLAN FORMULATION

I

The selection of an improvement plan from among the alternatives, the

details of the preliminary design and the implementation procedure of the

selected improvement plan are presented.

Table 31. Advantages and Disadvantages of Proposed Alternatives.

I

I

11.1 Plan Selection

The selection of an improvement plan was primarily based on the economic

analysis. The economic analysis was on a reach-by-reach basis and this allows

combinations of the alternate plans to be considered. Besides the results of

the economic analysis, selection of a plan is based on the inherent advantages

and disadvantages as related to construction, maintenance, and implementation.

Before recommending the final plan selection, the advantages and disadvantages

of each alternative are discussed below and presented in summary form in

Table 37.

I

11.1.1 Plan Evaluation

Alternative
2 3 4
Detent I on w' th DetentIon with
"As-Is" Channel tzation En I arged Cu I verts Ra I sed Ro ads
Poss I b I e Ad vantage
Effectl.... redJctlon of peak ru nof f X X X
RedJctlon of cap Itol cost X X
Aesthetics X X X X
Multipurpose capabilities X X
Improvements of water quality X X
Ease of 1"I'Iementotlon X
Pub 11 c acceptance X
Sediment control X X
RedJce pond I ng X
Possible DIsadvantages
Maintenance X
Land requirements X X X X
Pub lie acceptance X
Safety requirements X
Structural requirements X X X
Impact of peak flows X
Cop ltal costs X
Site suitability X X
Benefit cost ratio X X X

I

I

I

I

Alternative 1 has the economic advantage of low construction costs. This

is an attractive alternative when flooding is confined to a narrow valley

channel. However, there are some disadvantages. First, there is no guarantee

that flood damage reduction will occur because existing roadways may still be

overtopped and the~e is no guarantee that the required legislation will be

implemented to avoid further development in the flood plain. Another disad-

vantage is the indirect costs associated with legislation, nondevelopable pro-

perty and future flooding are not considered. Also, it does not solve the

existing problems which occur at the channel crossings where roads are over-

topped, below culverts where scour occurs and at locations where maintenance

I

I

I

I

should be done.

I

Alternative 2 is an intensive capital improvement program. It requires

channels, with excessive right-of-way acquisition, which must be maintained.

Most openings on channel crossings must be enlarged which will cause temporary

disruption in the community. The peak flows are increased due to the loss of

natural storage behind road embankments. However, it does solve the problem

of ponding behind roadways and prevents overtopping of roads during most

storms. Channelization would stabilize the banks since channel designs

include reduced velocities and mildly sloped banks.

I

I

I

I

69