FLOOD00076

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Title: Floodplain Study Review and Designation program - SOQ
• Date: 4/1/2000
• Prepared For: State of Colorado
• Prepared By: Sear-Brown Group
• Floodplain - Doc Type: Miscellaneous

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BIG DRY CREEK FLOODPLAIN IMPROVEMENTS
BIG DRY CREEK AT 1-25

WESTMINSTER, COLORADO

www.searbrown.com

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CLIENT NAME
City of Westminster, Colorado

REFERENCE
Sheila Beissel
303-430-2400

PROJECT COST
$ 1,012,700.00

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COMPLETION DATE
1999

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1991.)
APWA Public Work..
Project of the Year

The Sear-Brown Group analyzed several alternatives to
remove the City of Westminster's wastewater treatment plant
from the IOO-year floodplain along Big. Dry Creek. The
combination of the Interstate 25 crossing over Big Dry Creek
and inadequate channel capacity adjacent to the plant resulted
in this entire facility being potentially flooded. Alternatives
included additional pipe capacity underneath the downstream
1-25, protective levees, crossing improvements on Huron
Street along the upstream side of the plant, drop structures,
channel realignment, and channel armoring. Analysis of the
preferred alternatives was completed using a mixed-regime
HEC-RAS hydraulic model.

Final design plans and specifications were ultimately prepared
for a trapezoidal paved bridge waterway with a supercritical
improved inlet at Interstate 25. This component was selected
to concurrently address the problems of pressure flow at the
bridge, sediment transport over the full range of flows,
protection of bridge piers and abutments from scour,
provision of base level for stream stability against headcutting
upstream of the highway, and cost-effectiveness. The final
design configuration of the Big Dry Creek channel along the
south side of the wastewater treatment plant was an erosion-
control fabric and riprap stabilized north bank with enlarged
flood channel capacity. Construction observation services
were provided during construction of the improved inlet and
bridge waterway at Interstate 25 to ensure conformance with
design intent and a high-quality product for the City of
Westminster.

i.THE SEAR-BROWN GROUP

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