SOM: the bayarc rising tides competition

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 SOMthe 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.