FLOOD04566

• County: Boulder
• Community: Boulder
• Stream Name: Gregory, Bear Can, Bluebell Can Creeks, Viele Chan
• Basin: South Platte
• Title: Major Drainageway Planning Volume 1, Part C
• Date: 9/1/1970
• Prepared For: Boulder County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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condition. High flows will flood the cemetery as they have done hIstor-
ically; however, the roads in the outer boundaries of the cemetery will
be raised 8" to guide the flows back to the channel below. This channel
will have special lined banks to receIve the returning flood waters. At
the Anderson Extension Ditch the lined section passes under and changes
into a grassed section. Then a lined reach occurs from King Avenue to
downstream of Bluebell Avenue where the natural channel is used in a main-
tained condition and widened at the last and most severe bend. There the
channel is riprapped to the culvert under Broadway. A grass lined chan-
nel then flows past and through 3 sedimentation and storage ponds before
being intercepted in a special hydraulic structure. This structure will
produce the necessary characteristics to pass 800 cfs through the exist-
ing refurbished box culverts under the cenver-Boulder Turnpike. The
channel will curve around in a grass lined channel to the existing box
culvert at 29th Street. The grass channel then goes behind an existing
apartment complex and changes to a lined section when brought back to
the existing alignment. The lined section will end and the channel will
enter a grassy park and detention site below 30th Street. The channel
then changes from grass to lined section as right-of-way requires. At
Madison Avenue and 35th Street a large curved box culvert will be built
to redirect flow to the existing alignment down to the Wellman canal.
The grass channel then starts immediately, drops under the Wellman and
continues to the confluence with Bear Creek.

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Bear Canyon ~

The foothills basin of Bear Canyo~ Creek is relatively stable and un-
developed. No major construction is proposed within the foothills basin.
Steps should be taken to stabilize areas where erosion is evident and
to prevent future development which might cause erosion.

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Between the NCAR Land and Table Mesa 4th Addition a series of flood de-
tention-sediment retention reservoirs is proposed. A detention reservoir
would be designed to reduce the peak 100 year runoff from 2000 cfs to 1600
cfs. The retention reservoirs would be capable of storing approximately
16 acre feet of sediment and debris.* Below the reservoirs, through Table
Mesa Park, a wide, shallow channel Is proposed. Although the area might
be flood plain zoned, and left in its natural condition, serious erosIon
of the steep natural channel is likely. Such erosion could negate the
benefits of the Table Mesa Reservoirs, and SUbJect the remaining down-
stream channel improvements to damage and filling. The existing flood-
way within Table Mesa Drive must be widened, deepened and protected to
allow higher velocity flow. A r;prapped channel with retaining wall for
l,;ft turn lanes is proposed for this area. At Table Mesa and Broadway
the flow enters a box culvert which crosses both streets. Provisions
must be made at this point for water rights on the Anderson Ditch.

* 26,000 cubic yards