A Better Way to Dredge the Bay

Aug 3, 2015
Sejal Choksi-Chugh
by Sejal Choksi-Chugh

What if the Bay Area had no beaches where our kids could play, no wetlands protecting our shorelines and no more smelt swimming in our waters? 

Every year, millions of cubic feet of sand and mud—enough to fill the Transamerica Building ten times—are dredged up from the floor of San Francisco Bay. But dredging methods that are currently used contribute to erosion of the Bay’s shores and of the coast outside the Golden Gate, including San Francisco’s Ocean Beach. Harmful dredging methods also kill endangered fish.

Baykeeper is fighting to get the Army Corps of Engineers, which regularly dredges the Bay’s shipping channels, to end these harmful dredging practices in order to preserve our beaches, wetlands and endangered fish.

Most of the Bay is shallow, and sediments continually wash into it from rivers, creeks and the Delta. Dredging is necessary to keep the Bay’s shipping channels and harbors deep enough for large ocean-going ships to reach Bay and Delta ports. But there are better ways to dredge the Bay than those now in use—methods that keep shorelines from receding and help protect fish from extinction.

In the past, sediments from the Bay floor were contaminated with mercury, washed down as a result of the Gold Rush, when mercury was used in gold mining. The contaminated mud and sand were dumped far out in the ocean because they were too toxic to stay in the Bay.

Now, sand and mud at the bottom of the Bay are often clean enough that they could be used to restore Bay Area wetlands, but the Army Corps is still dumping too much into the ocean.

Wetlands are crucial to the Bay’s health. They provide habitat for wildlife, help prevent shoreline flooding and filter out pollutants. These marshy areas depend on the tides; they need time both underwater and above water for part of each 24-hour cycle. Tens of thousands of acres of Bay wetlands have been restored in recent decades, some as a direct result of Baykeeper’s victories. But they could be flooded as sea levels rise and keep them underwater 24 hours a day.

Some clean dredged sediments are being successfully used to restore wetlands that were degraded or destroyed for farming or development. As reported in Bay Crossings in March, when the Army Corps recently dredged the Port of Oakland, 400,000 cubic yards of sediment was deposited at a former wetland near Suisun Bay to help restore the threatened native habitat of endangered fish and wildlife.

Clean dredged mud and sand can be used more often to build up wetlands. When millions of cubic yards of clean sediment is instead dumped far out in the ocean, it robs the Bay of a resource that can help wetlands survive sea level rise and improve the Bay’s health. And it also contributes to another problem: erosion of Bay shorelines and of beaches outside the Golden Gate.

Mounting scientific evidence shows a connection between Bay dredging and some of the fastest rates of erosion on the West Coast. Accelerating erosion at San Francisco’s Ocean Beach, for example, threatens a major sewer line and the Great Highway. Sand naturally washes out the Golden Gate and up onto Ocean Beach and other coastal beaches, if it’s not removed from the Bay ecosystem and dumped far out in the ocean. Erosion is also being accelerated by private companies that are allowed to mine excessive amounts of sand from the Bay for use in manufacturing concrete—another destructive practice that Baykeeper is working to end.

In addition, harmful dredging methods kill endangered fish. One method, hydraulic hopper suction dredging, needs to stop now. Hydraulic dredging vacuums up sand, mud, and everything else that’s on the bottom of the Bay. That includes delta smelt and longfin smelt, two Bay fish species on the brink of extinction. The Army Corps’ own analysis shows that in 2011, their dredging killed up to 29 percent of the delta smelt population and 8 percent of the longfin smelt population. Baykeeper is challenging the government to use a technology that’s safer for fish: clamshell buckets, which scoop up mud and sand the way a backhoe would dig a pit. 

Baykeeper will keep up our legal actions until dredging in the Bay is done in ways that preserve our beaches, build up our wetlands and protect our important Bay species. To learn more about Baykeeper and support our work, please visit www.baykeeper.org/donate.

Photo: Gail Odom

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