Major wetlands restoration project reaches milestone
Completion of $20M levee helps provide flood protection
One of the largest wetland restoration projects in Marin County and San Francisco Bay reached a milestone with the completion of a $20 million, 2-mile-long levee just east of the Bel Marin Keys.
Two years in the making, this new taller and wider levee will eventually enable the California Coastal Conservancy to remove a preexisting smaller levee along San Pablo Bay and allow the water to restore about 1,600 acres of lost wetland habitat.
Amy Hutzel, the newly appointed executive director of the conservancy, said wetlands are the “vital organs” of San Francisco Bay, providing a multitude of benefits to wildlife and humans.
“The wetlands around San Francisco Bay are critical to the health of the bay, and we’ve lost up to 90% of them,” Hutzel said. “We’re working really hard around the whole bay to restore these wetlands. They sequester carbon, they improve water quality, they help with local flood protection, they feed the bay with nutrients.”
The massive wetland project near Bel Marin Keys began construction in late 2019. Led by the California Coastal Conservancy and U.S. Army Corps of Engineers, the Bel Marin Keys Wetland Restoration Project is the largest piece of the 2,600-acre Hamilton Wetlands Restoration Project.
Construction began on the Bel Marin Keys portion in late 2019 and was able to continue through the pandemic because the project was deemed to be critical. An army of tractors, excavators and other machines worked on the flat landscape, scraping up the peaty moist soils and hauling dredge soils to begin sculpting the new levee.
The new levee is up to modern standards and will provide greater protection
against sea level compared to the smaller existing bayside levee, according to the conservancy’s project manager Jeff Melby. The new levee is located much further inland from the existing levee, with the fields on the eastern side of it set to become new tidal marshland once the next phase of the project is completed.
The old levee along San Pablo Bay is about 60 feet
wide while the new levee ranges from 270 to 400 feet wide. The new levee is estimated to last about 50 years based on current sea-level rise trends but is designed to be built higher as needed, Melby said.
If completed, the project will advance a regional goal to restore 100,000 acres of wetlands in San Francisco Bay. In the 19th and 20th
centuries, settlers diked and drained wetlands and marshes to make way for agriculture, development, salt fields and other uses. About 90% of the bay’s original wetlands, or about 200,000 acres, were lost by end of the 20th century.
At the Bel Marin Keys site, the wetlands were transformed into agricultural lands. As the peaty soils were exposed to the air, however, they began to subside to the point where the land is now about 10 feet below sea level. The subsidence was caused by the organic material in the soil releasing carbon dioxide as it was exposed to the air.
As a result, the land is vulnerable to flooding as has had happened in recent years when the bayside levee is breached, with the resulting cleanup and repairs costing hundreds of thousands of dollars.
In addition to restoring lost habitat and ecosystems vital to the health of the bay, these projects also provide a cost-effective, multifunctional defense against flooding and sealevel rise for nearby coastal communities, according to San Francisco Estuary Institute senior scientist Letitia Grenier.
“With climate change, we’re starting to appreciate marshes even more because we desperately need the shoreline protection they provide,” Grenier said. “They also mitigate climate change because they sequester carbon.”
Aside from the levee, the project will include a new pump station behind the new levee to ensure the new tidal inundation does not flood surrounding communities.
Additionally, the project will restore habitat for endangered species native to the bay including the Ridgeway’s rail and salt marsh harvest mouse, Melby said.
Marin state representative Sen. Mike McGuire, DHealdsburg, and a representative of Assemblyman Marc Levine, D-Greenbrae, toured the new levee on Nov. 19.
“In total, 1,600 acres of wetlands near Bel Marin Keys are being restored and public access is a key component,” McGuire wrote in a statement this week. “This incredible transformation is made possible due to the dedicated efforts of the State Coastal Conservancy, Novato Baylands Stewards and dozens of community volunteers. The state stands ready to continue our partnership and we love seeing the fantastic progress.”
The next phase of the Bel Marin Keys project that will involve flooding the land will be much more extensive in scope and significantly costlier. However, project leaders say much of the estimated $105 million phase could be funded by the $1.2 trillion federal infrastructure package signed by President Joe Biden.
“I see it as a kind of a once-in-a-generation opportunity to tap into a significant funding source,” Hutzel said.
Before the old bayside levee can be broken, the land must be sculpted into a form that would allow for tidal marshlands to be created.
“If we breached the bayside levee today, the site would most likely not evolve into vegetated tidal marsh because it’s too low,” Hutzel said. “And it would also have impacts on the existing marshes and mudflats in the North Bay because it would be sucking in a lot of water and sediment.”
To create the right conditions for wetland formation, the U.S. Army Corps of Engineers plans to pump in dredged sediment from the bay. As much as 16 million cubic yards of sediment, or about 1 million large dump truck loads, may be needed, though the conservancy is studying whether less can be used.
Construction is not expected to begin for another three to four years and the building itself will take several years to complete. Hutzel said the U.S. Army Corps of Engineers typically dredges about 1.5 million cubic yards of sediment from the bay in locations such as the Port of Oakland.
“I think it’s going to take some time for the corps to do the design work and for us to get all the permits necessary to move it forward,” Hutzel said.
The project is using similar methods during the first part of the Hamilton Wetlands Restoration Project when 648 acres of marshland near the Hamilton Army Airfield was restored in 2014.