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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ENVIRONMENTAL GOALS AND OBJECTIVES

7.3

Historic broad floodplain & diverse hydrologic regime
compressed. Riparian breadth & diversity limited.
Flood conveyance limited.

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The principal environmental goals related to this master plan are to

Maximize the opportunity to re-establish long-term health and function of the stream corridor
in conjunction with flood improvements
Minimize impacts to healthy plant communities,

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Among

and water quality

was published

Woody riparian species native to this area "do not regenerate in their own understory
and depend upon periodic disturbances to create suitable germination sites"... "In the
absence of major natural disturbances or human intervention, the reduction in cover by
native tree species is inevitable...catastrophic flooding or active management will be
necessary to increase native tree cover" (Gershman, 1999).

Frequent flood terrace &
regeneration of native
trees/shrubs lacking or limited.

In the Fourmile Canyon Creek corridor, due to the lack of a frequent flood terrace, the opportunity for
flooding to regenerate native vegetation is very limited. Spill of major flood events to the
Wonderland Creek tributary further reduces the effectiveness of a large flood event to affect
regeneration of native vegetation. Re-establishing a functional channel morphology and substantial
flood conveyance would restore a medium for native species regeneration and planting.

channelized & confmed.

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wildlife habitats,

In 1999, a riparian habitat assessment report of the City of Boulder tributaries
the conclusions for the City's tributaries overall was the following:

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Excavation of a flood channel would afford the opportunity to enhance the stream ecosystem and
restore many ecological functions and values now lost. Specifically, restoring the integrity of the
channel restores the capability of the vegetation and habitat to regenerate. Re-establishment of a
defined and diverse active channel and frequent flood terrace is emphasized. The broader the
excavation, the broader the riparian terrace established, and the better the opportunity to create a
highly functional and valuable habitat. Where proposed improvements include excavation of the
channel invert in a broader flood channel, opportunities to re-establish some stream meanders and
aquatic diversity are increased. Yet channel excavation requires that existing vegetation be removed.
The two principle environmental goals identified are, therefore, somewhat contradictory. The greater
the long-term benefit of the design, the greater are the short-term impacts, and vice-versa.
Nevertheless, both goals are appropriate, and the balance between the two must be carefully
considered in the preliminary and final design processes

~ Aquatic habitat structure &
diversity lacking.

Frequent flood terrace & regeneration d.l
of native trees/shrubs lacking or limited \

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Conditions

Figure 7-2
Existing Channel

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7-7

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