The Promenade at Amargosa Creek is a 545,000 square foot
development project that will contain 1.2 million square feet of
store and restaurant space encompassing a total of 157 acres.
“In order to prepare the land for development, we needed to
enclose Amargosa Creek and infill the original open channel
to provide a buildable site,” said Jon Cantrell with the City
of Lancaster. “Amargosa Creek is a natural earthen channel
that bisects the site and during large storm events, the
creek alignment widens beyond its original dimensions. This
uncontrolled event prevents the site from development without
significant creek modifications.”
The City needed an underground conveyance channel that
would be easy to maintain, not erode, provide for infiltration into
local watersheds and provide for a buildable site. Originally, the
City considered using reinforced concrete box (RCB) structures
to underground the creek; however, they realized that standard
RCBs may be cost prohibitive and prevent water recharge.
After researching cost effective and long-lasting channel
alternatives, the City worked with Penfield & Smith, the
engineering firm on the project, to design both precast concrete
and metal plate arches for the project.
A 3,705 foot, 28-ft. x 10-ft. SUPER-SPAN™ plate structure was
used for the majority of the channel alignment. Future plans for the site include the construction of a medical
center, thus a portion of the channel required a precast structure to support the building loads. A 535 foot
long, 28-ft. x 10-ft. CON/SPAN
® Bridge System was used where the channel crossed under roadways and future
building sites.
“The invert of these arch culverts was lined with ArmorFlex®
articulating concrete porous pave blocks to allow for the
stormwater runoff to infiltrate through while also providing
maximum scour protection,” said Brianna Daniels, Senior
Engineer with Penfield & Smith. “They also provided for great
infiltration and easy maintenance.”
The ArmorFlex blocks provide for a firm surface to accommodate
City maintenance equipment via a maintenance ramp that
was fenced and landscaped to provide safety and pleasant
aesthetics. Cass Construction installed 71,268 square feet of 50L
blocks and 36,932 square feet of 70L blocks.
“We were very comfortable with the SUPER-SPAN, CON/SPAN
and ArmorFlex products throughout the design phase,” said Ray
Hunt, Capital Engineering Manager with the City of Lancaster.
“Our main concern was getting a solid contractor through the
bid process and Cass did a great job for us. The products were
installed like we expected and it went without a hitch.”
“The speed with which the products were installed, as well as
outstanding project coordination with the City’s Public Works
Department, were extremely beneficial in limiting the exposure
inherent to working within a federally regulated waterway
during the rainy season,” added Matt Goubeaux, Estimator /
Project Manager with Cass Construction. “In fact, the project was
completed not only on time, but a few weeks ahead of schedule.”
The undergrounding of the earthen channel also brought
up many environmental concerns and right-of-way issues
that required the involvement and coordination of several
government agencies, utility companies and property owners.
“In addition to hydraulic analyses and FEMA coordination,
two Streambed Alteration Permits through the Department of
Fish and Game (DFG) were prepared,” said Cantrell. “We then
designed and constructed mitigation improvements including
landscaping the side slopes of the Creek with native plant
material.”
Construction for the Amargosa Creek Underground Conveyance Project began in June 2009 and was finished
by December 2009. The system is now fully operational from a flood control standpoint, and the City is
currently completing the final landscaping. The SUPER-SPAN, CON/SPAN and ArmorFlex products have already
proven successful as the current water flow has now been controlled and there has been no scouring, a factor
which was critical for successful implementation. The City was also acknowledged by local water purveyors for
their porous invert design, allowing for local water recharge.