FLOOD05827

• County: Boulder
• Community: Boulder
• Stream Name: Boulder Creek
• Basin: South Platte
• Title: Boulder Creek Phase B
• Date: 12/1/1979
• Prepared For: Boulder
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

The existing diversion structure for the Boulder White Rock Canal,

located downstream of the Broadway bridge, would be removed and replaced

with a side channel diversion structure approximately 350 feet upstream

of the Broadway bridge between the library and the Municipal Building.
Approximately 700 feet of 68" x 43" reinforced concrete oval pipe would
be provided to convey water diverted by the new diversion structure to
the Boulder White Rock Canal. The maximum capacity of the proposed
diversion is estimated to be 150 c.f.s.

Between Broadway and Arapahoe, the north overbank of Bo~lder Creek would

be lowered and a series of low terraces supported by simulated rock

retaining walls approximately three feet high would be provided. The

proposed terraces would be protected against erosion by buried rip-rap

underlying the restored, landscaped surface.

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southwest of the Childrens Library and the Fire Department Office
Building east of the Childrens Library would be removed in conjunction

with the proposed excavation and retaining wall. Access to the Childrens

Library would be provided by a footbridge between the Childrens Library
and the proposed retaining wall.

BROADWAY TO ARAPAHOE
The existing diversion structure downstream of the Broadway bridge would

be removed and replaced, as previously described, with a side channel

diversion structure located approximately 360 feet upstream of

Broadway. The removal of the existing diversion structure would allow

approximately five feet of streambed to be excavat8d; increasing the

total available flow area through the Broadway bridge. The depth and
adequacy of the existing abutment and pier footings would be inves-

tigated and improved as required in implementing this proposed improve-

ment.

The area downstream of the Boulder Publ ic Library would be excavated to

provide additional flood conveyance. The Fire Department Office Building
parking lot to the south of Boulder Creek, would be lowered approximately
five feet. A retaining wall would extend from the east side of the main

1 ibrary to the north abutment of the improved Broadway bridge. Access

to Boulder Creek from the north would be provided by two stairways on

the east and west ends of the library parking lot together with a ramp

for the handicapped adjacent to the east stairs.

The Broadway bridge would be improved by adding an additional 42 feet

span to the north that would match the unique architecture of the exist-

ing bridge by means of an arched facade. The proposed improvements

would provide approximately 2.5 feet of freeboard at the Broadway
crossing for the 100-year discharge of l2,000 c.f.s. Additional free-
board cannot be obtained by increasing the length of the proposed bridge
improvement because the water surface profile through the proposed

crossing is predominantly controlled by downstream conditions. Addi-

tional freeboard could be obtained by raising the bridge at the expense
of losing the unique architectural features of the existing Broadway

bridge.

The existing pedestrian bridge located 250 feet upstream of the Broadway

bridge would be removed and replaced with a swing-away bridge.

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