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lightering is estimated at $69 per ton in 1982 dollars. The basic de
sign solution to this problem is to build a rubblemound causeway extend
ing to a point sufficiently offshore so lightering vould be eliminated.
New Port: 3500 Foot Causeway
The ultimate port/causeway vould extend 3500 feet from shore and have a
short-term cargo storage in an "L" at the end of the causeway. Land
ward of the "L" are two piers to accommodate general traffic and poten
tially vessels associated with oil and gas development in the Outer
Continental Shelf of Norton Sound. Extensions could be made to greater
depths beyond the 3500 feet. The maximum draft of a fully loaded fuel
barge is 25 feet. A minimum underkeel clearance of two feet is added to
a three-foot allowance for tidal set down and vaves at the dock face.
A 30-foot depth for the deepest berth is provided for in the design.
Nearly completed In 1986 Is a rubblemound causeway extending 2500 feet
without an "L". Host barges can tie up to this facility. Fuel barges
requiring the 30-foot depth can anchor south of the end of the causeway
and pump fuel to the dock using a line stabilized with a bouy. When
more funding is available the causeway can be extended.
The process of designing the Nome port facility illustrates several
coastal management problems and effective solutions. Once this basic
design concept was arrived at, engineering analyses were carried out
to determine the structure that would withstand wave and Ice forces.
Height of the causeway and size of outer protective rock were the crit
ical variables to be determined by the analyses.
The armor rock weight is determined by taking the average weight needed
for the causeway structure head for non-breaking waves and the structure
trunk for breaking waves. A uniform weight of 20 tons was used for pre
liminary design. Assuming the quarry rock has a specific weight of 165
pounds per cubic foot, cubic blocks would have 6.2 foot long sides. The
east side of the structure will be well protected with respect to crit
ical waves but may be subject to attack by moving ice fields. According
to the physical model analysis, described in the section below on Ice
Impacts, blocks of about 8 tons vould not be substantially dislodged by
ice overtopping. These blocks would be heavier than armor estimated for
wave attack.
The armor rock weight needed to protect against wave forces is calcu
lated by a formula which includes slope of the causeway armor, at 1/1.5,
breaker height at 17.8 feet, and equivalent deep water wave length of
400 feet.
Waves at the causeway head and port structure vould not be breaking, if
it is assumed that the same wind that produced them will be conducive
to a 13-ft. surge. It was assumed that the corners at the head struc
ture would be rounded to avoid rock stability problems. Vaves vould
break at a depth of 21 feet, vhlch vould correspond to a chart datum
depth of 8 feet.