Rising tides cut through the restored wetlands of San Pablo Bay. Salvaged logs could be the answer

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Six years ago, an excavator drilled a hole in an earthen dike, sending a torrent of water from San Pablo Bay onto 1,000 acres of ranch. It was a spectacular first step towards turning back 150 years, before natural wetlands were dammed and drained to be cultivated for hay.

But the waters of the bay eat away at the limits of this reclaiming tidal region, a critical buffer between rising sea levels and infrastructure like Highway 37, a major artery for approximately 40,000 North Bay motorists every day.

Now the excavators are back at Sears Point Ranch to build a new type of living shoreline dike designed to prevent erosion.

A team of engineers and scientists working with the Sonoma Land Trust devised a new plan to create a series of wave shadows by forgoing traditional rock and concrete rip-rap and instead building a living seawall with salvaged logs, recycled gravel and other mostly natural materials. to allow essential native plants of salt marshes to take root.

By the time these materials biodegrade, scientists hope that native tidal vegetation and sediments will have had time to form a 6-foot-deep cushion between increasingly powerful tidal pressures and upland infrastructure. said Julian Meisler, Baylands program manager at the Sonoma Land Trust. .

“It’s not the first line of defense, it’s the only line of defense for Highway 37,” Meisler said.

Generations ago, coastal marshes bordered San Pablo and San Francisco Bays, absorbing the forces of storm surges and high tides. Most of these marshes have been dammed and processed for agriculture, salt ponds and other industries.

In 2005, the Sonoma Land Trust purchased the 2,327-acre Sears Point Ranch, once considered for a casino project, to begin creating a tidal reserve for native species, migratory birds and recreational trails.

Julian Meisler, Baylands Program Manager at Sonoma Land Trust.

Julian Meisler, Baylands Program Manager at Sonoma Land Trust.

Brontë Wittpenn / The Chronicle

Today, the old hay ranch is teeming with shorebirds in abundance. The land ranges from a muddy carpet for tiptoeing egrets to a rippling aquatic habitat at high tide dotted with mounds of native grasses and pickles.

But the tidal marsh is still in its infancy and waves have started to carve deep benches in the slope of the marshes near an innermost sea wall, Meisler said. Rail lines, working farmland, a network of recreational trails and the road itself are at risk.

The team is now placing several hundred eucalyptus and Douglas-fir logs in trenches dug in the muddy bottom of the swamp. Workers anchor the logs with cables and secure them in the mud with branches of coyote brush. They add reused gravel to create a gentle slope on the eroded escarpment behind the logs, creating a gravel beach for the growth of more native grasses.

The hope is that these structures will absorb enough forces from the water to allow native marsh grasses to establish and spread. The California Wildlife Conservation Board is funding the $ 900,000 project to build this 2.5-mile living seawall.

Native plants like Pacific cordgrass and pickle provide the muscle needed to adapt to rising sea levels, said John Callaway, a wetland restoration ecologist at the University of San Francisco. Thousands of blades and stems anchored with deep roots can absorb a large amount of energy from tidal forces and storms.

Native plant species known as pickles are planted here in a new Sonoma Land Trust project to create a "living shore" which helps to combat erosion and sea level rise.

Native plant species known as pickles are planted here as part of a new Sonoma Land Trust project to create a ‘living shore’ that helps fight erosion and sea level rise .

Brontë Wittpenn / The Chronicle

They do this by retaining volumes of sediment that build up over time and are essential for dealing with pressures from storms and rising seas, Callaway said. Although the natural supply of sediment from the rivers and streams feeding the bay is decreasing, agencies are turning to dredged mud from the bay’s shipping canals to help build these tidal buffers.

The more these wetlands can grow and rise with the buildup of plants and sediment, the more resilient the shores of the bay will become, Callaway said.

“With the fires and all that people have been through over the past few years, people are much more aware that climate change is not something to think about in 50 years, it is happening now,” Callaway said. “And we have to prepare for it immediately. “

Log structures are not entirely natural, but they are designed to mimic a kind of wooded infrastructure that has reinforced wetlands in the past. Generations ago, before the Sacramento River was dammed, channeled and rebuilt, a Douglas fir could tip over into a rushing winter stream in the Sierra Nevada and end up being hundreds of miles away in the Bay of San Pablo.

Today, large machines are needed to transport these logs in wet areas. Meisler said Caltrans and Pacific Gas and Electric donated logs removed from roads, cleared from utility lines or salvaged from burn areas, saving the trust approximately $ 130,000 in materials and labor. land.

Pile of eucalyptus logs at Sears Point Ranch near Novato, California.  The Sonoma Land Trust installs over 200 logs on the muddy bottom of the bay to prevent erosion when reclaiming intertidal wetlands.

Pile of eucalyptus logs at Sears Point Ranch near Novato, California. The Sonoma Land Trust installs over 200 logs on the muddy bottom of the bay to prevent erosion when reclaiming intertidal wetlands.

Brontë Wittpenn / The Chronicle

There is no guarantee that the living riparian system will work, Meisler said. And it could take five or 10 years to see the results.

But a clue to the power of these herbs can be found just above the sea wall to the west. Rolling herbs and rusty pickles cover 830 acres of reclaimed ranches flooded in 1996 by the Land Trust and the California State Coastal Conservancy.

The eye barely detects water under the lush green, red and yellow foliage with fluttering red-winged blackbirds. Meisler said it might take another 10 or 20 years to see the swamp bounce back, but they have natural forces in their corner.

“The more we try to stop these powerful forces, the more trouble we get,” Meisler said.


Julie Johnson is a writer for the San Francisco Chronicle. Email: [email protected] Twitter: @juliejohnson



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