The Rock Islands have been designed
to prevent out of control shipping vessels from
running into one of the main span tower piers.
The rock island works to stop a ship before it
ever hits the tower by causing it to run aground.
Each rock island is approximately one acre above
the water and extends down to five acres across
the bottom of the riverbed. They are constructed
with three sizes of Newfoundland limestone.
The bases of the two rock islands
are constructed with twelve shiploads of small
Newfoundland quarry stone. It took six days for
the stone to travel from Canada’s most easterly
province. When it arrived in Charleston, the stone
was loaded into one of two different types of barges
depending how it was to be used to form the island.
Stones placed on “bottom-dump” barges
were released directly into the river to form
the perimeter of the island. Stones placed on
“flat top” barges were picked up
by a clamshell bucket and placed in precise areas
around the drilled shafts.
Once the quarry stone had been
placed for both islands, 3 shiploads
of 160 to 300 lbs pieces of armor stone are placed
on top of the quarry stone. After the medium stone
has been placed, approximately 2 shiploads of
the large 2400 to 4000 lbs armor stones were placed
around the tower footings where waves strike the towers.