typical tidal conditions . the bayarc project
image courtesy SOM

the san francisco bay conservation and development commission (BCDC) recently
hosted an international architecture competition for ideas responding to sea levels rising
in san francisco bay and beyond.

international firm SOM design was one of the six winners of the rising tide competition.

the bayarc is a minimal, lightweight and environmentally sensitive system designed to
protect the san francisco bay area from periodic high water levels associated with sea level rise.
it operates on organic principles of buoyancy and the structural efficiency associated with
net membranes and tension. it is a concept that has the potential to eliminate billions of dollars
in permanent levees and localized bay area flood protection without compromising the bay's
system of ecology and commerce.


flood threat conditions
image courtesy SOM

the objective of the bayarc is to prevent the peak of extreme tide events while
maintaining a natural tidal exchange between the ocean and the bay.

the bayarc consists of a submerged, cable reinforced membrane anchored to the seabed
that utilizes a bladder embedded in a tensile leading edge fastened to structural pylons
at the water's edge. when deployed the bayarc floats to the surface and its tensile membrane
creates a barrier stretching from the water's edge to the sea floor.

the top cable of the bayarc is connected to anchors on each side of the golden gate bridge
holding the membrane in place. a small amount of tidal or wave energy is captured
by flotation devices at each anchor. this energy is used to compress air over time and is
released quickly when the bayarc is deployed. the principle forces on the membrane result
from drag during deployment as well as the hydrostatic imbalance due to the differential
water level between the ocean and bay. the resulting gentle arc is a direct consequence
of these forces. the arc's curvature in plan directly echoes the arc of the golden gate bridge's
primary cables. the curvature is derived from the bay's depth the arc's material properties
and span.


flood threat conditions - cut away view
image courtesy SOM


l: the golden gate during typical condition r: cross section through golden gate while deployed
image courtesy SOM


tensile membrane stress diagram showing relatively modest stress levels; greatest at center and least at ends
image courtesy SOM

when the peak tide is projected to rise above a threat level, the bayarc is deployed.
it remains deployed only until the high tide peak has passed 'shaving off' the peak into the bay.
as the falling ocean tide approaches the bay, the bayarc drops and rest on the sea floor as
the currents begin to reverse flow. as noted below projections for sea level rise by 2050
would require deployment for only a few house per day and only a few times per year.