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Custom
designed recoverable intake structure for the Cornell intake.
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A plan view of the designed pipeline alignment is shown
above. The pipeline runs through a tunnel from the heat exchanger facility to
the lake shore where it is initially dredged into the bottom to maintain
clearance from small boats and winter ice floes. When the pipe reaches water
depths of 15+ feet it sits directly on the sediment covered lake bottom making a
broad turn to the North as it heads for deeper water.
The lake bottom drops off very gradually at first requiring a mile of
pipe to reach a depth of 35 feet. Then
from this depth the slope increases and the pipe is laid over the most gradual
portion of the steeper slope down to the intake depth of 250 feet.
This was the first pipeline Makai had ever done in a fresh
water lake, and it held several design challenges. While the
currents and waves predicted in the lake were small compared to those
experienced in the ocean, they were large enough to require a unique anchoring
system to hold the pipe safely due to the weak sediments which
cover the lake bottom. Steel shear plates were
designed to be coupled to the concrete pipe anchors, and these plates were
driven into the bottom after pipeline deployment. Makai subcontracted Haley and Aldrich, Inc. of New York to
assist in the geo-technical investigations and onshore aspects of this work.
The pipeline design life of 75 years and the concerns for
existing aquatic species in the lake required careful design consideration.
Makai decided early in the design that it was both prudent and technically
feasible to design a recoverable intake structure for this pipeline. This would
allow both detailed inspection and maintenance to be performed on this critical
portion of the pipeline over its entire service life without the need for
decompression diving. The natural flexibility of polyethylene pipe made such a
development possible. The last
600’ of pipe were lightly weighted, and the intake structure was designed with
special buoyancy modules that could be air-filled to allow it to float on the
surface. The intake structure on
the bottom is shown above. The intake can be
recovered from the surface using a derrick barge or barge mounted winch.
In addition, a stainless steel screen structure was designed that
can be separately recovered; its purpose was to keep fish and other aquatic
species out while allowing large water flows to pass through at minimal head
loss. Separate recovery of this screen will allow it to be cleaned of Zebra and
Quagga mussel growths when necessary.
 The deployment of the Cornell intake was challenging
because of the large diameter of the pipe and the limited access to the lake for
large tugboats. The contractor used
Makai's controlled submergence process to deploy the pipeline in multiple sections.
Makai carried out extensive analysis to analyze several
possible deployment scenarios and also conducted scaled model tests of the HDPE
flange connections to ensure that they could safely withstand the expected
bending and tensions during deployment. The pipeline was installed in the Fall
of 1999 with final completion during 2000.
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