Issues in Infrastructure: Climate Change
Lake Mead Intake No. 3
By Penelope Grenoble, Source Editor
The Intake No. 3 structure is secured within a moon pool in preparation for being lowered to the bottom of Lake Mead.
14 SOURCE fall 2013
intake tunnel were constructed under two separate contracts
with Barnard of Nevada, Inc. and Renda Pacific and have been
completed. Construction of the three-mile intake tunnel is
expected to be completed in 2014.
It took eight months to construct the 1,400-ton intake structure
on a 110-foot wide by 160-foot long barge of modular pontoons
anchored on the shore of Lake Mead. The structure is a 96-foot
high 16-foot ID stainless steel riser casing coupled with a concrete
base section. The tunnel boring machine (TBM) excavating the
tunnel will dock with the base section by boring through a soft
eye designed into the base. Because the design of the base section
called for closely spaced large-diameter rebar within the forms,
self-consolidating concrete was used. The structure was installed
in a 95-foot wide by 159-foot long by 83-foot deep underwater pit
and backfilled with tremie concrete. Excavation of the intake pit
approximately 300 feet below lake level took almost two years and
required 23,000 shaped blasting charges.
The barge and intake structure were towed to the site. The
structure was lowered through a moon pool on the barge using a
system of four 500-ton jacks and placed at the bottom of the pit
on a guiding frame in one continuous 48-hour operation. Because
divers couldn’t work at this depth due to the water pressure, a
remotely operated vehicle (ROV) monitored and guided the
Lake Mead Intake No. 3 (1,200 MGD) was approved by the
Board of Directors of the Southern Nevada Water Authority
(SNWA) in 2005. Its purpose is to protect existing water
system capacity against the potential loss of existing Intake No.
1 due to continuing drought on the Colorado River (the lake
has dropped over 100 feet since 2000 and is now roughly at half
capacity with surface near elevation 1,100 feet above sea level).
Secondarily, the new intake will supply higher quality water
to SNWA’s existing River Mountains and Alfred Merritt Smith
Water Treatment Facilities.
The overall project contract calls for a submerged water intake
at elevation 860 and a three-mile intake tunnel and interconnecting
tunnel to an existing pumping station. A planned new
pumping station and discharge pipeline and its electrical feeder
have been deferred to a later date due to economic constraints.
A $447 million design-build contract was awarded to Vegas
Tunnel Constructors (VTC), a joint venture of S.A. Healy Co.
(Lombard, IL, USA) and Impreglio S.p.A (Milan, Italy). VTC’s
contract includes a 600-foot deep shaft, the three-mile 20-feet
internal diameter intake tunnel and the intake riser. The
fabrication and placement of the intake riser was also part of
this contract and is complete. The connecting tunnel to divert
water to existing Intake No.2 and modifications to the existing