More than 100 years after the California gold rush, developers and city guides filled San Francisco Bay and shrunk it by a third to build farms, highways, airports, and subdivisions.
All of this changed in the 1970s with modern environmental laws. But now, with sea-level rise threatening to cause billions of dollars in flooding over the coming decades, the bay needs to be refilled – but in a different way this time, according to a new scientific report released Tuesday.
Twice the amount of sediment excavated for the Panama Canal is needed to rebuild the bay’s coastline, researchers say, to protect communities in Marin County and elsewhere from catastrophic flooding and rising seas that stretch to the end of the Panama Canal could grow up to 6 feet tall by the century.
The Bay Bridge, which spans San Francisco Bay, can be seen from above in San Francisco on October 9, 2015. More mud and debris is needed to increase the height of the marshes and mud flats that encircle the coast of the bay to combat rising sea levels. (Josh Edelson / AFP via Getty Images)
The best source of this immense fill volume is the mud and mud that are scooped up when the bay’s ports and shipping channels are dredged each year. Currently, however, this material is being dumped into the ocean 60 miles from the Golden Gate or sent to the bottom of the bay near Alcatraz Island.
“We waste too much,” said Barbara Salzman, executive director of Marin Audubon, whose organization is trying to use dredged material for the planned restoration of the Tisconia swamp in San Rafael’s flood-prone canal district.
“We really need to use the sediments as a resource,” said Salzman. “I hope we can use this and get a regional program off the ground.”
The report calls for a radical change in these disposal practices.
“It’s not a waste product. It’s a valued resource. It should be used for the common good, ”said Letitia Grenier, co-author of the report and senior researcher at the San Francisco Estuary Institute, a nonprofit research organization based in Richmond.
The study, titled “Sediment for Survival,” was authored by scientists at the San Francisco Estuary Institute with input from researchers from UC Davis, the US Geological Survey, the Environmental Protection Agency, the San Francisco Bay Conservation and Development Commission, and other Bay experts .
The math is pretty simple.
To add 6.9 feet to the wetlands and tidal flats around the bay over the next 80 years, 477 million cubic feet of mud and debris must be added. That corresponds to a load of 48 million dump trucks.
If nothing is done, between 150 and 170 million cubic meters naturally enter the bay from streams, rivers and other sources. This leaves a deficit of around 300 million cubic meters. The good news? Grenier and her colleague Scott Dusterhoff estimate that around 60% of this deficit can be compensated for with mud and mud from dredging. The rest can be produced by scooping out large amounts of sediment trapped behind dams, removing dams, diverting flood protection projects, or relocating internal debris from construction projects in future generations.
Using a waste product to protect the bay from flooding would be a societal shift recognizing that aluminum cans and glass bottles cannot be thrown into landfills or that sewage can be purified and reused for irrigation, said David Lewis, executive director of Save the Bay, an environmental group in Oakland.
“Let’s stop wasting this precious resource and use it to protect our communities and wetlands before sea level rise inundates them,” he said. “There are places where we have to raise dikes and sea walls. But in most parts of the bay we can use the natural infrastructure. And that costs less than sea walls and brings more benefits. “
A flock of herons gathers in wetlands near the west side of Dumbarton Bridge in Menlo Park, California on Thursday, July 23, 2020. (Anda Chu / Bay Area News Group)
These benefits include habitat for birds, fish, and other wildlife, and recreational trails available to the public.
Civil engineer Roger Leventhal of Marin County Flood Control and Protection District said Marin is at the forefront of reusing dredging sludge, sand and other materials for wetland restoration and flood control projects at Novato Creek and for a planned project at Gallinas Creek nearby McInnis Park.
“We agree that sediments must be used wisely to help adjust sea level rise in the Bay Area, and this is something we are already making progress on in Marin County,” said Leventhal.
San Francisco Bay has risen 8 inches since 1900, according to tide gauges. In hotter temperatures, the polar ice caps around the world melt and the volume of sea water increases. Scientists predict the bay will rise by 1 foot or more by 2050 and another 3 feet or more by 2100. Severe winter storms are already causing flooding in some parts of the Bay Area, especially at high tide.
Rising sea levels threatens to flood major transport arteries in Marin, including Highway 101, Highway 37, and cut off communities like Marin City from emergency services and basic needs. Thousands of homes and businesses in bay communities like Mill Valley, San Rafael, Corte Madera and Larkspur could be inundated with water by the end of the century, changing the lives of thousands of residents.
Billions of dollars of infrastructure, including high tech corporate headquarters like Facebook and Yahoo, sewage treatment plants that serve millions of people and communities like Alviso and Foster City, are at risk.
The Facebook offices are located near wetlands in Menlo Park, California on Thursday, March 11, 2021. (Anda Chu / employee archive)
San Francisco International Airport has a $ 587 million plan to build a large new steel and concrete levee around the entire 10-mile perimeter of the airport and its runways, on which 55 annually Millions of passengers are handled. The Santa Clara Valley Water District is working to build earthen levees in parts of the South Bay. And in 2018, San Francisco voters approved a $ 425 million bond to start work on a huge 30-year $ 5 billion project to rebuild the Embarcadero seawall from Giants Stadium to Fisherman’s Wharf to begin.
But around much of the rest of the bay, researchers say, it’s cheaper and more environmentally friendly to increase the size and elevation of wetlands.
Lewis said a key challenge is convincing the Army Corps of Engineers, the federal agency that does most of the dredging, to change its longstanding practices. Dredging materials have been used to haul and pump them on a number of projects, including 648 acres of wetland restoration at Hamilton Airfield in Marin County and 566 acres of restored marshland at Montezuma Slough in Solano County. However, the practice is still in its infancy and some soils contaminated with PCB, DDT and other old toxins cannot be used or need to be buried and sealed.
Another major challenge is the price tag. Disposal of dredged material off Alcatraz costs about $ 10 per cubic meter, about $ 20 in the ocean, and about $ 30 in the Hamilton and Montezuma wetlands, said Jim Haussener, executive director of the California Marine Affairs & Navigation Conference, an organization that represents ports and ports.
Haussener said “beneficial reuse” of dredged spoil is a good idea, but if the federal or state governments fail to provide further funding, he fears that local ports will either not be dredged as often or their fees will rise.
“Everyone supports it,” he said. “The question is who pays?”
IJ reporter Will Houston contributed to this report.