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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Wetlands Can Help San Francisco Combat Sea Level Rise

By Catherine A. Cardno, Ph.D.

A report authored by 100 scientists and 21 management agencies recommends wetlands to mitigate the effects of sea level rise in the bays in the San Francisco area.

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The creation and maintenance of wetlands can help the San Francisco Bay area remain resilient against sea level increases without the need for construction projects, a new report reveals. NPS

November 10, 2015—Rising global temperatures, melting artic ice, and rising sea levels are creating multiple issues that coastal communities must address if they hope to become resilient in the face of natural disasters. Within the United States, planning on the East and Gulf coasts must include the effects of hurricanes and their associated storm surges, among other issues. On the West Coast, much of the attention is given to earthquakes, but rising sea levels there must also be addressed if its coastal areas—the low-lying San Francisco Bay area, for example—hope to adjust without losing the valuable infrastructure that often extends along the coastlines.

A new report, The Baylands and Climate Change: What We Can Do, released last month and authored by 100 scientists and 21 management agencies, recommends mitigating the effects of sea level rise in the San Francisco Bay Area by using wetlands. The report focuses on the steps necessary to maintain a resilient ecosystem in the Bay area through 2100, and is an update of the 1999 report Baylands Ecosystem Habitat Goals , which calls for the establishment and maintenance of 100,000 acres of habitable tidal marsh.

Geographically, the "baylands" are the wetlands present in a series of bays that hinge at the Golden Gate, the strait that connects the San Francisco Bay to the Pacific Ocean. The bays extend from Suisun Bay, which is fed by the Sacramento and San Joaquin rivers in the north, through the Carquinez Strait, into San Pablo Bay, which is fed by the Napa River, above the Golden Gate. 

While the catastrophic flooding associated with storm surges on the East and Gulf coasts—created by such hurricanes as Katrina and Sandy—will not be an issue in the San Francisco area, multiple simultaneous levee failures due to a massive earthquake, strong El Niño storms, and existing nuisance flooding will all be exacerbated by rising sea levels, according to Jeremy Lowe, a senior environmental scientist in the resilient landscapes program at the Richmond, California-based San Francisco Estuary Institute. Lowe was one of the chapter cochairs responsible for the report's findings. 

"We're on the West Coast—there are physical reasons why we're not going to have a hurricane," Lowe says. "We're not going to get a big, 13-foot storm surge, we're going to have a 3-foot storm surge." This smaller storm surge makes wetlands a highly practical and effective solution in the Bay Area. 

"Each natural system can accommodate certain ranges of waves and water levels," Lowe says. "In New Orleans and Louisiana, where you're trying to stop a hurricane storm surge, you need miles of wetlands," he explains. "And here we need hundreds of feet of wetlands to do the same job. So it's a different scale." 

As useful as wetlands will be to attenuate the strength of waves—and storm surges—heading toward shorelines, such solutions will work only in shallow, low-lying areas in which there is already suitable land available. Lowe explains: "We have a lot of opportunities…but we're not going to be able to use marshes in front of San Francisco itself because of its deep water almost immediately [offshore]. If you look at Oakland, these are hard areas, [and] we're going to continue to build concrete sea walls. I don't think there's any dispute about that. But we need to explore ways we can soften their impact on the environment," he says. 

The ways in which civil and environmental engineers work together to design more nature-based mitigation strategies offers a preview of what may be a long-lasting design trend, according Letitia Grenier, Ph.D., the resilient landscapes program director for the San Francisco Estuary Institute and the lead scientist for the report, who wrote in response to questions posed by Civil Engineering online. "Natural infrastructure is self-maintaining and cost-effective, but careful design and engineering need to go into how these systems dovetail with the built environment," Grenier said. "Civil engineers will be critical to considering how wetlands can allow us to build smaller levees behind them (rather than large levees with no wetland protection) and reduce the need for sea walls.

"My hope for the future lies in great part with civil engineers," Grenier added. "Rather than the…paradigm I often hear [involving] engineers constructing a concrete solution to any environmental problem, I see that the art and science of civil engineering is evolving to more elegant and multibeneficial solutions that use the forces of nature to achieve the desired outcome." 

The report offers five strategies that the authors believe should be implemented in the Bay Area. Those strategies are to restore estuary-to-watershed connections, design complexity and connectivity into the baylands, increase coordination among baylands stakeholders, create plans that factor in ecological outcomes, and engage the citizenry in supporting these efforts.

The five strategies can be brought to fruition through 10 actions, the report says. These 10 include the first two items in the list of strategies, as well as restoring and protecting complete tidal wetlands systems; restoring the baylands to full tidal action; planning for the baylands to migrate; actively recovering, protecting, and monitoring wildlife; developing and implementing a comprehensive regional sediment-management plan; investing in planning, policy, research, and monitoring; developing a regional transition zone assessment program; and improving carbon management in the baylands.

One of the reasons that wetlands are seen as such a viable option in the Bay Area is that while the area has lost much of its wetlands over the last few centuries, many of the ecological elements that made them possible—land, sediment, and water—are still there, according to Lowe. If those elements can be reconnected, reestablishing the wetlands is a relatively straightforward process. "You don't need to plant the salt marsh themselves—they usually reestablish given the right conditions of elevation, sediment, and tidal connection," Lowe notes. "There are [already] seeds spread by the flow of the water." And with navigation and flood management channels in the bays already requiring regular dredging, the availability of material to build up the wetlands is readily available. 

With the creation of the correct elevation, "the marshes tend to look after themselves, given space and a supply of sediment," Lowe says. "We know how to do those relatively quickly and with good certainty about when and how it's going to work." It is critical to acknowledge, though, that the reestablishment and management of wetlands is an ongoing program, and not just a one-time project, Lowe cautions. 

The concern is that with rising sea levels, the water is rising faster than sediment can be naturally deposited in the wetland areas, Lowe says. To combat this the report recommends developing a short-cycle, ongoing program so that every few years the navigation and flood management channels are dredged and the sediment from that work is placed a few inches deep on the wetlands so that the necessary elevations can be maintained. Currently, channels are dredged on much longer time cycles.

Now that a solution has been identified and consensus recommendations issued by so many experts and agencies, funding must be found—and quickly. "It takes a few decades to get [wetlands] established and mature," Lowe explains. "With sea level rise accelerating, we've got to do this sooner rather than later, because by 2030 or 2040 we want to make sure that we've got a lot of our marshes at least in place and growing."

In addition, Grenier foresees that "designing these future landscapes will take greater crossover and discussion between traditional engineering and traditional ecosystem science," as she explained it. "Both fields will probably need to become more interdisciplinary in the long term.

"At this point in the history of urban development, we realize that working with nature provides better quality of life in the long term," Grenier noted. "Now our technology and shoreline planning need to quickly catch up to envision new solutions using natural infrastructure to create a healthy and protective shore."


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