FLOOD01279

• Designation Number: 215
• County: Boulder
• Community: Boulder
• Stream Name: Boulder Creek
• Title: Flood Hazard Area Delineation - Boulder Creek
• Date: 1/1/1983
• Designation Date: 5/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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advised to contact the Urban Drainage and Flood Control District or the City
of Boulder to determine if the information in this report has been amended.

- BASIN DESCRIPTION -

- ACKNOWLEDGEMENTS -

Boulder Creek and its tributaries drain a total of 440 square miles at its
confluence with St. Vrain Creek, approximately five miles east of Longmont
(Figure 1). The headwaters of Boulder Creek originate at the Continental Divide
at elevations as high as 13,500 feet (NGVD). The stream flows eastward through
steep,narrow mountain canyons about 22 miles before reaching the canyon mouth
near the western city limits of Boulder, at about elevation 5,400 feet (NGVD).
Boulder Creek continues in an easterly direction through the City of Boulder,
for a distance of approximately 4.8 miles. After passing through Boulder, the
creek flows 18 additional miles in a northeastward direction across the high
plains to its confluence with St. Vrain Creek. St. Vrain Creek is tributary
to the South Platte River.

This report was prepared by Muller Engineering Company, Inc., Consulting Engineers
of Lakewood, Colorado, under contract with the Urban Drainage and Flood Control
District.

Topographic mapping, digitized cross sections, and survey data for stream cross-
ings were provided by Reids Aerial Mapping of Denver, Colorado. Original mapping
was prepared with two-foot contour intervals at a scale of 1" ~ 100' (Reference 1).
The final mapping was reduced by 50-percent for printing in this report.

The mapping was prepared according to the specifications of the Urban Drainage
and Flood Control District. Ground control surveys for the topographic mapping
were performed by Miller - Ernstsen & Associates, Inc., of Englewood, Colorado.

The study area includes the reach of Boulder Creek beginning at Valley View
Road, a short distance above the confluence of South Boulder Creek (Drainage
Area ~ 155 square miles), and ending just downstream of the Arapahoe Avenue crossing
at the mouth of Boulder Canyon (Drainage Area ~ 130 square miles). Two-mile
Canyon, Bear Canyon, Gregory Creek and Sunshine Canyon are the major tributaries
to Boulder Creek with their confluences lying within the study reach.

The hydrology used in this study was completed by the U.S. Army Corps of Engineers,
Omaha District (Reference 4).

- FLOOD HISTORY -

Since 1864, the City of Boulder has experienced five major flood events on
Boulder Creek, ranging in estimated discharge from 2,500 cubic feet per second
(cfs) to 13,000 cfs, resulting in light to severe property damage. All floods
for which dates are known occurred in Mayor June. The flood of June, 1894, the
greatest flood of record at Boulder, had an estimated peak discharge of 13,000 cfs.
The estimated frequencies of these five major events range between 10- and
100-years as determined from the discharge probability relationships developed
by the U.S. Army Corps of Engineers (COE).

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