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Are Wetlands Nature's Best Defense Against Sea Level Rise?

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Flooding near the Bay Bridge during an extremely high tide. Photo by Michael Filippoff
Flooding near the Bay Bridge during an extremely high tide in December 2012. Photo by Michael Filippoff

QUEST Northern California coordinating producer Lindsey Hoshaw contributed to this story.

A new report from Stanford University indicates that conserving wetlands is critical to defending coastal communities from a rising sea.

With nearly 50 percent of the nation’s population projected to live in coastal counties by 2020, sea level rise could affect millions of people.

Sea level is rising because the ocean is warming, which increases the ocean volume, and also because ice sheets and glaciers are melting. Storm surges and ‘king tides,’ the highest tides of the year, can contribute to short-term coastal flooding.

Global sea level is predicted to rise 3 feet by 2100, but that number can vary widely in different geographic locations where the land is either rising or sinking and may be tectonically active.


In the Bay Area, sea level is predicted to rise by at least 1 foot, and could rise by up to 5 feet, since it is situated on several fault lines. Over the last century, sea level in the Bay Area has already increased by 7 inches.

“We don’t need to look in the future, Highway 101 is flooded every year,” Heidi Nutters from the San Francisco Bay National Estuarine Research Reserve said.

On-ramps to Highway 101 in Sausalito are flooded every year by king tides. “Sea level rise and storms that cause flooding will only get worse in the future because of climate change,” Nutters said.

horizontal levee

To prepare for the deluge, land managers, planners, scientists and engineers are already working to explore and develop possible solutions. One option involves using wetlands as natural buffers against sea level rise.

Wetlands have been shown to be really effective at buffering sea level rise and flooding,” said Hilary Papendick, a National Oceanic and Atmospheric Administration Coastal Management Fellow. “Not only do they have benefits for water quality but they also provide habitat for different species,” Papendick said.

However, more than 80 percent of intertidal habitat around the bay, that might have been useful as a buffer to rising tides, has been lost to development. It has been diked and drained for salt production and farming, or filled, paved and turned into highways, railroads, and sewage treatment plants.

Jeremy Lowe, a wetlands scientist with consulting firm Environmental Science Associates, is working with the Bay Institute to evaluate the concept of “horizontal levees” in the bay.

The California Clapper Rail, an endangered species, would benefit by the expanded habitat provided by a "horizontal levee." Photo courtesy of Robert Stronck, stronckphoto.com
The California Clapper Rail, an endangered species, would benefit from the expanded habitat provided by a "horizontal levee." Photo courtesy of Robert Stronck, stronckphoto.com

A “horizontal levee” is an expanded marshland in front of a manmade levee. By maintaining a wide tidal marsh in front of a manmade levee, urban areas are buffered from sea level rise.

Specifically, the marshland on the seaside of the levee can decrease the size and power of the incoming waves. It can also serve to buffer the incoming water and decrease the wear and tear on the levee.

“The lowlands, wetlands and mud flats have formed a resilient shoreline for a long time,” Lowe said. “We’re trying to incorporate these features into our planning of an urban estuary in the 21st century.”

Lowe’s firm, along with state agencies, utilities, universities and other consulting groups are collaborating on a demonstration project for a horizontal levee led by the Oro Loma Sanitary District. Though it’s still in the developmental phase, Lowe hopes that such demonstrations will allow this and similar concepts to be tested, refined and implemented on a larger scale in the next couple of decades.

Endangered species, such as California Clapper Rail and Salt Marsh Harvest Mouse, could also benefit from the additional habitat, helping to improve their chances of rebuilding sustainable populations.

While the horizontal levee moves from concept to demonstration, it becomes one more tool in the toolbox to consider in preparing for sea level rise. But Lowe notes that it will take more than wetland restoration to fully combat sea level rise.

“It’s not a silver bullet, but it buys us some time,” Lowe said.

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