FLOOD02930

• Designation Number: 341
• County: Boulder
• Community: Boulder
• Basin: South Platte
• Title: FIS - Boulder - Volume I
• Date: 5/3/1990
• Designation Date: 3/1/1993
• Floodplain - Doc Type: Floodplain Report/Masterplan

and losses along Fourmile Canyon Creek have generally been low,
because the area is primarily undeveloped.

Significant flooding along Goose Creek occurred in August 1951 and
July 1954. The 1954 event damaged an addition to the Community
Hospital, ~hich was under construction.

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These floods are just a few that have occurred in the area.
Major, area-wide floods also occurred in 1904, 1909, 1914, 1921,
and 1923. During May 1973, flooding caused an estimated $70,000
worth of damage. No estimates of the recurrence intervals of the
historic floods have been made. There has been little
documentation of flooding on Wonderland, Elmers Twomile, and Skunk
Creeks.

.,

There is
throughout

a history
Boulder.

of

debris

blockage

and

flow

diversions

2.4 Flood Protection Measures

Past urbanization in the City of Boulder has encroached drainage-
ways and reduced stream storage, thereby increasing runoff peaks
and volumes. Undersized culverts and channels exist throughout
the city. A few measures have been taken to alleviate these
problems on some of the study streams and are discussed below.
This discussion excludes drainage improvements constructed to
provide protection from erosion. The degree to which the flood-
control measures discussed protect from return interval floods is
unknown at this time.

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Flood-protection measures along Wonderland Creek consist of
Wonderland Lake (Reference 5); the ponding area between Wonderland
Lake and Broadway; the channelization projects along the Winding
Trail Village and Aspen Grove developments, located between the
Longmont Diagonal and 26th Street (Reference 6); the recently
constructed 26th Avenue Crossing culvert and drop inlet
(Reference 6); and the detention pond east of 47th Street
(Reference 7). Wonderland Lake, whi le not designed to provide
flood protection, will attenuate the 100-year peak floodflow from
400 to 100 cubic feet per second (cfs). For the routing analysis,
Wonderland Lake will be considered filled to the spillway crest at
the time of storm runoff routing. The area between Wonderland
Lake and Broadway creates an unplanned flood-control structure,
because the culvert at Broadway will convey very little flow and a
considerable ponding volume is available. This unplanned flood
reservoir was not included in the hydrologic analysis. Diversion
flow from Fourmile Canyon Creek to the north will also reach
Wonderland Creek at this location.

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The 26th Avenue Crossing culvert
constructed and are designed to
(Reference 4). The pond east of
effect on the 100-year peak flow.

and drop structure have been
contain the 100-year floodflow
47th Street will have little

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