What may be the future surface of San Francisco’s sea wall is being assembled in an expansive warehouse near Mission Bay.
Instead of constructing one continuous surface, a team of welders and engineers with the Port of San Francisco are fabricating a series of steel platforms festooned with textured tiles to test whether grooves, curves and divots will attract native marine species or promote biodiversity within the Bay.
For now, this project is purely experimental. This summer, the port in partnership with the Smithsonian Environmental Research Center (SERC), will submerge this “living sea wall” at three different locations along the Embarcadero and monitor the tiles for a minimum of two years.
The pilot represents one way The City is taking inspiration from nature to bolster infrastructure against worsening impacts of climate change including rising seas and stronger storm surges.
“With climate change and sea-level rise and the need for flood protection, there’s a movement to focus on nature-based resiliency,” said Kelley Capone, a project manager with the port’s waterfront resilience program at a recent Port Commission meeting. “This means re-imagining how sea walls are designed.”
Once diverse and thriving ecosystems, most of the world’s coastlines have been paved over and plugged with concrete pilings, resulting in vertical, barren surfaces. While effective for holding back tides, these walls, known as “gray infrastructure,” create inhospitable environments for marine life that depend on tidal zones to spawn, feed and survive.
“What we’re hoping for is that the more textured structure will attract a broader range of species, including a number of different seaweeds that exist in San Francisco Bay, which in turn are foundation species for lots of other organisms,” said Chela Zabin, one of the SERC scientists overseeing the pilot. “We’re really thinking about all of the things that can inhabit the rocky shores, including different types of snails, barnacles, mussels, oysters, chitons — all of those sort of organisms.”
These shapeless surfaces may also negatively impact native species, Zabin said. “The current status quo of the smooth sea wall already tips the balance towards invasive species,” said Zabin, who added that invasive species have the upper hand in adapting to a variety of conditions. “Taking some of the elements of the natural rocky shore and adding them to the sea wall, would that tip the balance in favor of more new species? That’s a question we have,” she said.
Although San Francisco is not the first to engineer a sea wall that more closely mimics nature, the pilot is one of the first to account for rising sea levels by suspending the tiles, made from a blend of concrete and oyster shells, across different various elevations to understand what happens at different tidal zones, including the subtidal zone, which is fully submerged.
“What is our intertidal today is going to be subtidal tomorrow – it’ll be underwater,” said Andrew Chang, an ecologist at SERC. Because of this, it’s important to understand how creatures use the tiles that spend most of their time underwater, he said.
San Francisco’s current sea wall is a 3-mile stretch of rock and concrete that protects more than $100 billion in assets, annual economic activity and regional transportation infrastructure. But at over 100 years old, it is seismically unstable and long overdue for replacement. By some estimates, it will need to be raised as much as 7 feet in the coming years to prepare for rising tides.
But it will be years, if not decades, before the project, a massive undertaking estimated to cost hundreds of millions of dollars, will be fully realized. “It’s a generational thing,” said Randy Quezada, the port’s communications director. “These lessons really are about how do we green this kind of gray infrastructure as we plan for the future.”
The findings from this pilot will also inform other projects that will need to happen across the more than 500 miles of Bay shoreline, said Tim Felton, deputy director of port maintenance at Port of San Francisco.
Still, some argue that throwing up sea walls is not a sustainable solution. Recent research out of Stanford University found the addition of sea walls along the Bay shoreline could increase flooding for communities throughout the region and cost hundreds of millions in flood damages.
“The more you put up sea walls, the higher the water becomes,” said Arthur Feinstein, Sierra Club California executive and longtime conservationist. “It becomes the bathtub. You fill it up. It’s got nowhere to go. And so it goes up.”
While Feinstein concedes San Francisco’s sea wall is critical to The City’s infrastructure, he hopes to see the region invest in actual nature-based solutions, like wetland restoration, instead of mimicking nature artificially. “Wetlands are our biggest tool,” he said.
Even so, Feinstein is optimistic the pilot project is an important step toward improving the green infrastructure of the Bay. “It’s comforting to know that The City is at least trying to do what it can when it has no option but to do something that is harmful ecologically,” said Feinstein. “It’s better than just a straight up and down piece of cement, but we can’t pretend that it’s the answer.”
Instead, he said, the region needs to stop developing in low-lying areas that are at the highest risk for flooding and convert more land back to wetlands, which play a critical part in buffering against storm surges, sequestering carbon, filtering pollutants and supporting critical habitat.
“I don’t know of anybody who will say ‘we shouldn’t have a sea wall around San Francisco,’” he said. “But wherever we have to use gray infrastructure, then at least let’s make it as ecologically positive as possible because a living Bay is pretty important to us. We have to try everything we can to keep it going.”