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

Fourmile Canyon Creek drops 400 feet throughout the study reach. The overall channel slope is
approximately 2% or 100 feet per mile. Generally, the slope of the Fourmile Canyon Creek
flattens as it flows eastward.

STUDY AREA DESCRIPTION

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LAND USE

The study reach is predominately developed with a mixture of residential and commercial
properties. The commercial development is located in the vicinity where Broadway crosses over
the Creek. With the exception of some in-fill and redevelopment, future land use will remain
very similar to existing land use patterns

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GENERAL

The study area includes approximately four (4) miles of Fourmile Canyon Creek located in the
within the northern portions of the City of Boulder. Portions of the study reach are also located
within Boulder County, Colorado. The study area is shown in Figure 1-1. The downstream limit
of the study is the Railroad Bridge immediately east of State Highway 119, (Boulder-Longmont
Diagonal). The upstream limit of the study area is the western edge of the Boulder City limits
located near the mouth of the canyon.

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The majority of the Fourmile Canyon Creek corridor is located within the City of Boulder and is
located within dedicated right-of-ways or easements. However, the creek corridor between Violet
Avenue and 26th Street is located on private property within unincorporated Boulder County.

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Large parcels of City of Boulder open space designated lands exist near the mouth of the canyon
and in the vicinity of 47th Street and at State Highway 119 within the Fourmile Canyon Creek
corridor.

The City of Boulder's, Parks and Recreation Department owns four separate parcels along
Fourmile Canyon Creek. Foothills Community Park, currently under development, is located on
the south bank near the mouth of the canyon. The Violet parcel is an undeveloped park site
located along the south bank between Broadway and Violet Avenue. The Elk's parcel is an
undeveloped park site located along the north bank of the stream between 26th and 28th Streets.
The Soccer Complex is a developed park site located south of the creek and west of 47th Street.

The City of Boulder's Housing Authority is currently developing affordable housing in the
Foothills Housing Development along the south bank of Fourmile Canyon Creek, west of
Broadway.

Fourmile Canyon Creek in the canyon upstream of the study reach, will generally maintain a base
flow year round. In the spring and early summer, Fourmile Canyon Creek, within the study
reach, will also maintain a steady base flow. However, as the summer progresses, the water seeps
into the alluvium east of the mouth of the canyon and sections of the creek become dry for much
of the year and will only experience flows during and immediately after a storm. East of 30th
Street the base flows often reappear. Portions of these base flows are reportedly due to leakage
from the Farmers Ditch crossing.

FOURMILE CANYON CREEK CHANNEL

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Mankind has heavily influenced Fourmile Canyon Creek within the study reach. The majority of
the channel has been channelized at some point over the last lOa-years and much of the
development along the Creek encroaches on the historic floodplain right up to the channel bank.

TOPOGRAPHIC FEATURES

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Redevelopment of the Village Center area located east of Broadway on both sides of Fourmile
Canyon Creek is currently in the planning stages. The City of Boulder is proposing the building
of a public library on the north bank as part of the redevelopment. Additional information for the
development planning in this area can be found in the North Boulder Subcommunity Plan, City of
Boulder Department of Community Design, Planning and Development, adopted 1995.

Fourmile Canyon Creek, is approximately eleven (11) miles in length, has a tributary watershed
area of approximately 10.2 square miles, generally flows from west to east and discharges to
Boulder Creek. The western half of the Fourmile Canyon Creek watershed is located in the
foothills west of Boulder. The eastern half of the Fourmile Canyon Creek watershed is located
east of the foothills.

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Crestview Elementary School sits south of the creek and west of 19th Street.

Two irrigation ditches cross Fourmile Canyon Creek. The Silver Lake Ditch (5 cfs decree water
right) crosses Fourmile Canyon Creek in an elevated pipe located west of Broadway. The
Farmers Ditch (50 cfs decree water right) crosses Fourmile Canyon Creek between 26th and 28th
Streets. The ditch crosses the creek in a pipe resting in the invert of the channel and creates a
drop of approximately 3 feet. Both ditches have provisions to dump excess ditch water into
Fourmile Canyon Creek.

IRRIGATION FACILITIES

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Fourmile Canyon Creek, between the canyon mouth and approximately 19th Street, flows on
deposits of an alluvial fan. The deposits are both stream deposits and debris flows with stream
flows dominating. The channel is currently incised in the alluvial deposits and portions of the fan
do not appear to be actively aggrading. In the area west of Broadway, the alluvial fan to the north
of the channel is slightly higher then the fan to the south.

An historic channel, located north of the existing channel, between the mouth of the canyon and
Broadway, is clearly evident upon field investigation. However, this channel has been partially
filled by recent residential development and is no longer actively conveying stream flows

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