FLOOD10390

• County: Boulder
• Community: Boulder
• Stream Name: Fourmile Canyon
• Basin: South Platte
• Title: Fourmile Canyon Creek - Major Drainageway Planning - Phase A Report - Alternatives Analysis
• Date: 6/1/2000
• Prepared For: UDFCD, Boulder
• Prepared By: Love & Associates
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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The review ofthe initial alternatives revealed the following:

ALTERNATE DEVELOPMENT

6.

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configuration and allow for

.uration:

Maintain the existin

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6.2

INTRODUCTION

6.1

channel

This alternative would include revising the regulatory 100- and 500-year floodplains for both
Fourmile Canyon Creek and Wonderland Creek to account for the existing spill flows.
Floodplain regulations would be strictly enforced, floodplain information and education
programs would be undertaken, and flood insurance would be recommended to property
owners within the reach. Debris cleanup and routine maintenance in the floodplain would be
required at regular intervals and following flood events

This alternate would maintain the existing floodplain,
continued spill flows to Wonderland Creek.

A large number of alternatives were initially identified to mitigate the existing floodplain damages
that occur along Fourmile Canyon Creek. The initial alternatives were screened and evaluated to
determine which of these alternatives would be studied in greater detail and which alternatives would
not be considered for further investigation. This chapter discusses the initial identification of possible
alternatives and the process used to identify the alternatives to be studied in greater detail.

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The existing creek has been altered by man over time. Road crossings have been constructed,
the channel has been straightened, the banks of the creek have been filled, and development
has encroached on the natural floodplain. In the purist definition, a "natural channel" would
be impossible to re-construct. Therefore, this term is defined in this report as a channel
designed by an inter-disciplinary team of engineers, geomorphologists and biologists, to
emulate a natural channel. Please refer to Chapter 7 - Environmental Assessment and
Opportunities for more information on this kind of channel design alternate,

nment:

historic channel ali

eneral

A natural t

6.2.2

initial alternatives

The

identified.

were

INITIAL AL TERNA TIVES

Early in the study a broad range of possible alternatives
where identified based on a number of factors including

6.2

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rovements:

This alternate would reduce the floodplain width at locations where it is excessively wide as a
result of significant man-made changes. Grade control structures could be constructed.
Bridges or irrigation structures could be replaced. Bank protection and erosion control could
be provided. The channel could be re-aligned. Low flow protection or velocity control could
be provided. Maintenance access to key locations would be provided.

Detention and/or Retention Facilities:

This alternate would provide flood storage to reduce the peak discharge of floodwaters and
related flood damages downstream of the facility. The flood storage could be designed to be a
multi-purpose facility with park lands, open space, and playing fields located within it.

with a high

and Channel 1m

rovements

Selected StructuralJm

6.2.3

uisition of Flood Prone Properties:

This alternate would identify structures located in hazardous areas and structures
flood damage potential to be acquired when they are placed for sale on the market

Ac

6.2.4

6.2.5

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The initial alternatives considered are presented in Table 6.1 in a matrix format. The left column of
the matrix contains the initial alternatives that were identified. The columns to the right indicate
which alternatives, on a reach-by-reach basis, were chosen for further consideration. A "Yes" in the
matrix indicates the alternative was determined to be appropriate for that reach and was chosen for
more detailed consideration. A ( - ) means the solution is not applicable. A "No" indicates the
alternative was determined to be inappropriate for further consideration. The decision on whether or
not to consider a specific alternative for further investigation was based on detailed discussions held
during the progress meetings and a cursory analysis of the factors listed above.

Floodplain Hydrology and Hydraulics
Existing Topography and Land Use
Impact on Wonderland Creek Floodplain
Environmental Considerations
Impact on the Existing Community
Existing Flood Damages
Potential Benefits
Input from Project Sponsors
Input from Public
Implementation Costs and Potential
Engineering Judgment
Regulatory and Permitting Requirements
Public Acceptance
City and County Boundaries
Future Development
Existing Planning Documents

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6.1

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