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 improved crossings will prevent the diversion of flood waters to the
north of Arapahoe Avenue, between 24th and 30th Streets, the one exception

being an area immediately to the west of the intersection of 28th Street

and Arapahoe Avenue.

For the Plan II I reach between 17th Street and Valley View Road (55th
Street) flood prone structures would be relocated if the cost to relo-
cate would be less than the present worth of flood damages. Additional
structures would be removed in the future if excessively damaged by
flood, fire, or other natural caUSes. The buildings remaining in the

flood plain after relocation would be flood-proofed if practical and if

the cost of the flood-proofing would be less than the present worth of

the expected damages.

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

28th Street
Remove the existing diversion structure downstream of 28th

Street and replace with a movable diversion, provide a con-

crete slope apron through the bridge to protect the existing

bridge piers and abutments.

A supplementary improvement consists of channel excavation between 24th

and 28th Streets in conjunction with the proposed improved crossings.
The proposed supplementary improvement would reduce the floodplain width

in this area and would prevent floodwaters associated with the IOO-year

discharge from inundating the commercial area adjacent to Arapahoe

Avenue between 24th and 28th Streets. If the proposed channel excava-

tion between 24th and 28th Streets is made, the channel must be re-

armored to prevent excessive degradation which would continue until a

new armor layer is established.

24th Street
Raise the low chord of the bridge six feet, extend the bridge

50 feet to the north and excavate to transition the improved

waterway opening into existing ground contours.

30th Street
Raise the low chord of the bridge four feet and extend the
existing bridge 45 feet to the north and 45 feet to the south
and excavate to transition the improved waterway opening into

existing ground contours.

Effects of Sherrelwood development, Eastpark development, and 47th
Street Parkway were not investigated during this planning study. Con-

struction occurred during the final stages of this study and the impacts

of these buildings, berms, and roadways will need to be resolved during

final design.

The proposed improved crossings at 24th, 28th and 30th Streets will
reduce the estimated water surface elevations immediately upstream of
these crossings approximately four feet for the estimated 100-year flood
discharge of l2,000 c.f.s. and not cause any additional flooding problems
downstream.

FLOOD PROOFING AND RELOCATION

The United States Army Corps of Engineers have recommended that all

future development within the 0.2%/500-year flood plain be flood-proofed

to the 0.2%/500-year flood elevation.

8