OAKLAND — Rising sea levels threaten not only structures around San Francisco Bay and the Delta but the shoreline marshes critical to the environmental health of the estuary, and the results could be “catastrophic” if action is not taken, scientists warned Thursday.
Predicted sea level rises of 3 feet or more by 2100 resulting from climate change could wash out and cover shallow tidal wetlands that act as important nurseries and habitat for wild fish, birds and other aquatic sea life, according to the scientific report on the state of the bay-Delta estuary.
To keep the wetlands from sinking under water, the scientists called for a major, sustained public campaign to build up and replenish those marshy areas with sediment.
Creeks, streams and rivers used to carry the silt and dirt naturally into the bay and Delta. Construction of dams, levees and shoreline developments, however, has largely cut off those flows in the past 160 years and also filled in most of the wetlands.
“We face a lot of problems if we lose our wetlands, and rising sea levels are making this an increasing challenge,” said Letitia Grenier, scientist at the San Francisco Estuary Institute, an environmental research and policy group.
The 100-page report by dozens of scientists in the San Francisco Estuary Partnership provides a comprehensive look at the environmental health of the estuary, the mixing zone for Pacific Ocean seawater and fresh water from California’s biggest rivers.
The document gave a mixed report card to the environmental condition of the bay and Delta.
Progress has been made in reducing San Francisco Bay water pollution and in restoring previously diked off wetlands to tidal action.
But rising sea levels, reduced freshwater flows from water diversions, declining wild fish populations and an invasion of non-native species like nutrient-gulping Asian clams have put the environment at risk, the report says.
San Francisco Bay is in “fair” condition overall, and the Sacramento San Joaquin River Delta and Suisun Bay are in “poor” condition because of many man-made changes, the report says.
“Bay wetlands are starved of sediment needed to sustain their growth, placing them in jeopardy from sea level rise,” the scientists wrote.
The threat to wetlands is manageable if the region can come up with a bold plan to replenish marsh areas with sediment, and designate some areas for wetlands to expand inland, said Josh Collins, chief scientist with the San Francisco Estuary Institute.
“The balance between water and sediment has been thrown out of whack,” he said. “Doing nothing is going to lead to very serious or catastrophic results. It takes a regional response.”
Options for fixes include trucking or piping in sediment trapped behind dams, or diverting dredge spoils now dumped in the ocean and putting them in wetlands.
Some scientists have suggested modifying dams to flush out the sediment-rich water at the bottom of reservoirs rather than releasing the more particle-free water at the top.
Collins said state, federal and regional agencies are trying to come up with guidelines on how to deliver the sediment.
On Wednesday in San Francisco, the Bay Conservation Development Commission kicked off a long-term effort to determine how and where to protect businesses, homes and other structures from rising sea levels.
In tandem with that effort, many government agencies are trying to determine how and where to protect or restore wetlands to act as a buffer against increasing flooding risks.
“Some of these marshes will serve as sponges,” said Zach Wasserman, the chairman of the Bay Conservation and Development Commission, “and there are other urbanized areas we will need to build up barriers to protect from rising waters.”
Wasserman said a public-private partnership called the San Francisco Bay Restoration Authority is considering sponsoring a Bay Area-wide ballot measure seeking a parcel tax next year to finance flood protection and wetland restoration.
Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.