FLOOD01787

• County: Boulder
• Stream Name: South Boulder Creek
• Title: South Boulder Creek/ Flatirons
• Date: 12/5/1997
• Prepared For: Boulder
• Prepared By: Consultants
• Floodplain - Doc Type: Community File

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Arapahoe Ridge subdivisions. Note that the MWE local drainage study
shows a higher discharge in the Wellman at 55th, but they use a higher one
hour local rainfall with larger peak intensities. At 55th Street more flow joins
the Wellman from Dry Creek Ditch No.2.
. The Wellman east of 55th would spill 700 cfs out of 900 cfs over the north
bank of the Wellman, which would flow north through the golf course. The
remaining 200 cfs returns to South Boulder Creek.
. All of the above flows are likely to be increased as the result of hydrology
model revisions.

LIMITATION AND RECOMMENDATIONS FOR FUTURE STUDY AND
INVESTIGATION

This study is an initial study. The following actions are recommended:

1. Refine South Boulder Creek and local hydrology including incorporation of
realistic rainfall and correction of tributary areas and other physical
parameters to best depict the watershed. This work could include field
surveys to more accurately depict the critical flow splits.
2. Conduct a floodplain study of the overflow including backwater analysis
using the results of the refined hydrology. Depict the flood limits on the
City of Boulder mapping. While the street flow depths in a 100 year event
are relatively shallow (generally 1.5 to 3.5 feet deep), the public should be
notified of the hazard.
3. Conduct a collaborative planning effort to mitigate a situation in which all
parties will suffer if the present situation continues. No easy solution exists.
A master plan is needed that would receive the support of most parties.
Such a plan will probably use a variety of hazard management techniques
and physical improvements to address both local drainage and South Boulder
Creek floodplain hazards.

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