The rock, wood and concrete protective walls that shield the east shore of Tomales Bay from rising seas are the subject of a new vulnerability report presented to Marshall residents last week. The Marin County Community Development Agency has completed a draft of the Tomales Bay Bulkhead Vulnerability Assessment, which analyzes sea barriers, from riprap buttresses to manmade earth embankments, along the five-mile section of shoreline from the Marconi Conference Center to Nick’s Cove.
George Clyde, a member of the East Shore Planning Group, said this was the first assessment of its kind. “I think it’s going to be just the starting point in figuring out how the business and homeowners are going to deal with sea-level rise,” he said.
The East Shore faces unique challenges due to the proximity of the shoreline to houses, businesses and Highway 1. A 2018 county adaptation report from Collaboration: Sea-level Marin Adaptation Response Team, or C-SMART, called for further investigation of the highway’s vulnerability along the East Shore to determine whether bulkheads below homes act as a secondary line of protection for the highway. The vulnerability assessment received $35,000 in funding from FEMA’s Hazard Mitigation Grant Program. (Marin has received over $10 million from the program).
According to the draft report, 23 percent of the bulkheads are in poor condition, 38 percent are in fair condition and 39 percent are in good condition. The barriers together span nearly 13,000 feet and 102 properties, roughly 75 of which are privately owned.
Mike Jewett, the lead author of the report, said he inspected the bulkheads over the course of two days.
“We picked days when tides were at their lowest so we could see as much as possible. For areas I could not get to on foot, I resorted to a day on the kayak,” he said.
The report lays out conceptual strategies to accommodate rising seas, including floodable crawlspaces, bulkhead reinforcement and natural protection in the form of habitat reconstruction. The draft notes that a combination of all three strategies will likely be considered, but that each case will be highly dependent on the structure, landscape and other unique factors.
The report points out that, because Marshall’s bulkheads are built from a range of materials, their repair and reconstruction styles will differ. In part of because of their proximity to the highway, each individual bulkhead will require its own professional evaluation, and because many bulkheads protect multiple properties, in some instances neighbors will need to work together to come to a solution, Mr. Jewett said.
“It’s highly likely that there will be multiple sites that can be fitted with very similar or identical designs—that’s not out of the question,” he said.
Residents expressed concern over the potentially long and expensive process that obtaining the proper permits and evaluations could require.
“If someone undertakes improvement to their house, will a required improvement to the bulkheads be triggered?” asked Helaine Kaplan-Price.
Mr. Jewett responded that such questions would be resolved by county planners.
Mr. Clyde said the assessment will serve as a basis for further studies, offering quantitative data that will help public agencies and private landowners address some of the challenges posed by sea-level rise.
The county still has not completed the hazards chapter of its updated Local Coastal Program, which addresses sea-level rise in the context of development in the coastal zone. Homeowners in West Marin have fought for the right to protect their homes with armoring strategies even as the California Coastal Commission has pushed back: The agency recently conditioned several permits for Seadrift projects on a ban of future armoring.
In the meantime, the county continues to plan for sea-level rise, said Kathleen Kilgariff, a long-range planning manager for the Community Development Agency.
“The best available science will continue to evolve, as will adaptation methods, so it’s really important to be having these meetings,” she said.