Shoreline management solutions at work.SeaBox
The breakwater box design is an open box of
concrete that can be floated into place and sunk to create an offshore
breakwater or used as a foundation for an ice resistant pier-groin.
Whereas different sizes can be used for specific situations, the ones we
are using in the middle Potomac River are 4 feet 9 inches wide by 2 feet 9
inches tall by 8 foot 6 inches long. Each box weighs 2.3 tons and is made
of minimum 5000 psi Department of Transportation Bridge grade concrete
with wire reinforcing. The boxes have a 1 foot 11 inch draft in the water
when empty and are placed so that they are over topped by waves at high
tide to allow the boxes to fill with entrained sand.
Two 4 inch diameter holes in the bottom
are filled with plumber's plugs while the box is floated into position.
These are simply pulled out to flood and sink the boxes in their desired
position. The plugs can be reinserted and the box pumped out and re
floated to allow for adjustment or changes in the erosion control
design.
The Breakwater boxes form a strong foundation for a pier in waters
where ice floes can damage or destroy piers or a boathouse. Instead of
driving treated piles into the riverbed, the boxes are used with 6 inch by
6 inch or larger posts bolted to the inside or outside of the boxes. 
The boxes can be bolted together close into
the shore to act also as a groin to build up a wider beach. Further out
they are separated to allow sand and water to bypass the boxes, allowing
deeper draft boats to use the pier while still providing mass to resist
the shearing forces of ice.