Stinson Beach sea-level report evaluates adaptation

In Stinson Beach — where the ocean threaten to swallow up streets and waterfront homes by the end of the century — building a defense against sea-level rise will come with tradeoffs, a new county report suggests.

The Stinson Beach adaptation options evaluation takes a look at the pros and cons of several possibilities, from construction of levees and protective dunes to wetlands restoration and more.

The report shows that there is a mix of landowners in the area, and suggests that projects would require community collaboration and compromise in a race against nature.

“One of the goals of this is to help people understand that there are a lot of considerations that need to be acknowledged before any action is taken,” said Isaac Pearlman, a planner with the Marin County Community Development Agency, the department leading the effort.

“This is not being prescriptive and we are not advocating for any specific adaptation strategy, but this is to help the community and local partners know what the tradeoffs are of each option,” Pearlman said. “I think that underpins the point that there is no one perfect solution.”

Bordered by both the Pacific Ocean and Bolinas Lagoon, the town of about 500 residents is in the vanguard of Marin communities most vulnerable to rising ocean waters.

Over the past couple of years, fierce “atmospheric river” winter storms pummeled the community. In January 2023, storms caused millions of dollars in damage to homes.

Last year, Marin County planners completed a six-month effort to update the sea-level rise projections that were first developed in 2016.

The results show that the beach, often seen crowded with visitors from throughout the Bay Area on warm summer days, could become inundated by the middle to late century. More than 600 homes would face permanent flooding by the end of the century.

Access roads such as Calle Del Arroyo and Highway 1 would face increased storm flooding with as little as 1 to 2 feet of sea-level rise, which the study projects would occur between 2040 and 2050. Nearby sensitive habitats such as wetlands around Bolinas Lagoon would be drowned by the end of the century.

A UC Berkeley and San Francisco Estuary Institute report published last year found that flooding issues in Marin would be exacerbated as saltwater intrudes into the groundwater table, pushing the less dense freshwater to the surface. Pearlman said these findings are especially important for Stinson Beach, given that residents rely on underground septic systems and utility lines buried underground.

The county’s new report evaluates 21 adaptation strategies, and rates each based on the engineering feasibility, environmental benefit, regulatory feasibility, social benefit and economic cost.

“There are some that are multi-benefit, including some nature-based solutions such as levees and dunes,” Pearlman said. “These stand out as interesting options because they offer flood protection and a range of habitat and environmental benefits as well.”

The report shows that projects like rock revetments and seawalls come with higher costs, but fewer benefits and greater hurdles.

The report shows there significant sea-level rise defense work is already underway.

The National Park Service is leading a parking lot rehabilitation project that includes adding a flood bypass channel to the ocean to help reduce flooding. Marin County Parks is working on a Bolinas Lagoon resiliency project that involves elevating roads to allow Lewis Gulch Creek to be reconnected with its historic floodplain.

Pearlman said Caltrans is also performing a sea level rise study of the Bolinas Lagoon, and residents are raising their homes above the floodplain.

Max Delaney, a resource protection specialist with the Greater Farallones and Cordell Bank National Marine Sanctuaries, is on the technical advisory group that worked on the report.

“There is nothing surprising in this report,” Delaney said. “We’ve been talking about this range of options over the years.”

Delaney said the sanctuaries are among the federal agencies on the North-Central California Coastal Sediment Coordination Committee, which is charged with identifying dredged sediment materials that could be repurposed for coastal projects, potentially some listed in the report. The county is a member of the committee.

Delaney said one of the objectives of that group is to brainstorm ideas, share progress on various efforts and learn how to collaborate on getting projects done.

“Our focus is really doing as much planning and adaptation to ameliorate and protect as much as possible the habitat and wildlife, and the county has the added challenge of protecting the private property,” Delaney said.

Jeff Loomans, who has owned a home in the town for 14 years, serves on the Stinson Beach Village Association’s sea-level rise committee.

“I think it’s a nicely done report and what I expected,” Loomans said. “My concern is, is there money to do this and the focus to do it? Where the rubber hits the road, or where the gravel hits the berm, is where you actually go out and seek funding.”

Pearlman said the next phase of the project will include a more detailed cost analysis that will identify funding sources such as grants.

A webinar to review the reports findings is set for 5:30 p.m. June 17. Participants must register online at bit.ly/3WZxnHr. The report documents are at bit.ly/3yDaaAy.