Watergate is a new coastal protection system concept that is automatically activated by sea level change.
As the tides rise past average peak levels, either through storm surge, or by climate change, Watergate’s buoyant hollow concrete boxes activate the first layer of flood protection.
The dynamic seawall, with a profile similar to the Ha-Ha of the English landscape garden, contains a concrete pontoon that rises with the current, maintaining a flood-gate 15 feet higher than peak tide. The second layer of protection comes when the hinged floating piers slowly swing shut when the pressure from rising water pushes against them. In addition to providing surge protection, the piers contain program ranging from swimming pools and oyster farms, to tide pools, boat marinas, and fishing spots.
When the gates are open the sea reaches the beach creating a swimming area with little to no rip-tide. The sandy depression created by the gates closure acts as a second line of defense, and basin for flood waters that find their way around the first line of defense.
The first line of defense is composed of hollow, precast concrete caissons, or pontoons, which are lifted into position by the very waters that threaten the city. A boardwalk parallel to the shore, the pontoons create a low-profile seawall allowing unobstructed views of the water during fair weather. Perpendicular to the shore, the pontoons create floating piers that, when water levels rise, swing slowly closed.
The second and third lines of defense are elevated, public egress and refuge zones on rooftops, tidal marshes, dune preserves, and other soft-scapes to absorb and contain water infiltration.
Beyond the walls, dune preserves act as a permeable basin for flood water to seep back into the ocean. In accordance with FEMA’s ABFE, the housing is placed on a 20’ high retail plinth supported by pylons. The zig zag form of the housing compresses the footprint allowing greater area for tidal salt marsh, while providing a greater number of units with sea views.
The tidal marsh areas provide key habitat for native and migratory species. Just as important, with the Watergate closed, the temporarily empty marshes will act as a gravity fed catch basin for inland flooding keeping the higher hardscape dry.
How Watergate works:
Water has a density of 1 gram per cubic centimeter, or 62 pounds per cubic foot. Solid concrete would sink but the caissons are hollow boxes. Even though the larger ones weigh 27,000 tons, they displace about 47,000 tons of water, far more than their own weight.
In short: the density of the total volume — air plus concrete — is less than the density of the equivalent volume of water.
The inclined roof of the housing blocks touch the boardwalk and street to allow ingress to the community gardens above the 20’ commercial plinth. These community gardens act as refuge areas during emergency conditions, where the public can walk to safety along a continuous on the roof.
The commercial plinth is composed of “raw” studio space, where entrepreneurs, makers, retailers, and artists can find affordable incubator spaces. The exposed concrete construction and operable storefronts, serving as floodgates, help insure the preservation of their stock, and minimizes damage to the building in a case where the first two lines of defense against storm surge is breached.
New York’s History of Concrete Caissons:
Pier 57 “Super Pier”. designed by Emil H. Praeger and built by the New York City Marine and Aviation Department, on the Hudson River at the foot of West 15th Street, Praeger was picked in 1949 to design a replacement for the Grace Line’s old Pier 57, which had burned down two years earlier.
During World War II, Praeger had worked on building the floating concrete caissons that were used to form artificial harbors on the coast of Normandy, France, during the Allied invasion of June 1944. He designed Pier 57 along the same revolutionary lines.
Pier57 Caissons floating down the Hudson
The caissons were fabricated in 1951 and 1952 in Grassy Point, N.Y., just north of Haverstraw and 38 miles up the Hudson from New York City. What made the location ideal was an artificial riverfront basin called Company Pond, a remnant of a clay pit that had been excavated by the Hudson Valley Brick Company.
Inside Pier57 Caisson
Other current concrete caisson flood barrier projects:
The Chioggia Flood Barrier, which is part of the MOSE Project, a storm-surge barrier being built in Italy to enable the Venetian Lagoon to be sealed off from the Adriatic Sea.
Monaco’s offshore waterfront extension is being built on 18 floating, prefabricated concrete caissons.
Historical Projects: Phoenix caissons, floating concrete boxes used in WW2, in Portland Harbor, UK
