Rising sea levels are a worldwide problem, but for the approximately 500-mile shoreline of the San Francisco Bay, one partial solution may lie in something that is actually quite small: the 1.5-mile-wide mouth of the bay, where the Golden Gate Bridge crosses. If water could be stopped from surging through that opening, the San Francisco office of Skidmore, Owings & Merrill (SOM) reasoned, much of the Bay Area could be saved from flooding.
After analyzing tidal patterns in the bay, SOM worked with a multidisciplinary team, including marine engineers from Moffatt & Nichol, to identify specific days and times within a day when flood risks were highest. Their BayArc tidal response barrier, a tensile net structure, lies dormant on the seafloor until high tides trigger its deployment, creating a temporary, but nearly impervious, wall across the bay’s mouth.
The flexible structure of cables and a waterproof membrane would unfold and rise, opening like a parachute filled by the water trying to squeeze from the ocean into the bay. Like a floating dam, its top edge would break the water surface, by approximately 1.5 meters, and keep most of the flow out. Once the surge dies down the structure would deflate, folding back onto the seafloor.
Using topographic data of the seafloor, the team developed 3D models of the bay and simulated the water’s motion to understand how the flows could be tamed, and how much water needed to be stopped to prevent flooding. They then designed the barrier’s structure, which comprises the membrane of plastic or Teflon-coated recycled rubber interwoven with a crisscrossed grid of stainless steel or carbon-fiber cables, like the vascular system of a leaf. When the barrier is engaged, the cable structure would completely be in tension. Wave-powered compressed air would help deploy the barrier.
See SOM's video of the BayArc's design and deployment here.
Though SOM has patented the system, the BayArc currently remains merely a concept for now. Other approaches to addressing sea-level rise in the Bay Area have been comparably scattered, focused on disparate segments of the shoreline as opposed to countering the problem head on, at the mouth of the bay. Though those community-based efforts are important for addressing local consequences, the region will soon need a more comprehensive plan, says SOM associate director Mark Schwettmann: “At some point, the magnitude of this problem will become apparent and there will be a cry for a more regional solution.”
The jury was impressed by the barrier's potential. Juror Mic Patterson said the project “represents the kind of strategic design innovation we need in response to the tremendous challenges presented by the accelerating impacts of climate change. Let’s build one and see how it works.”
Project: BayArc: A Tidal Responsive Barrier
Design Firm: Skidmore, Owings & Merrill, San Francisco · Craig Hartman, FAIA (concept and interdisciplinary leader); Mark Schwettmann, AIA, Alex Cruz, Ross Findly, David Kwon (project team)
Project Adviser: Moffatt & Nichol
Drawings: Skidmore, Owings & Merrill
Structural Engineer: Mark Sarkisian, Eric Long, David Shook, Geoffrey Brunn
Marine Engineering Concept: Moffatt & Nichol · Dilip Trivedi, Richard Dornhelm