Report looks at adapting to sea-level rise


Climate experts predict that sea levels could leap as much as 70 inches by 2100, and Marin County is preparing to be on the frontlines. The Community Sea-Level Marin Adaptation Response Team, C-SMART, has released a draft adaptation report that presents options for increasing the resiliency of natural and built assets along the coastline. The Community Development Agency, which is spearheading the response team, is accepting public comments on the draft through June 23.

“We’re ahead of most other counties on preparing for sea-level rise,” county planner Jack Liebster said at a meeting at the Dance Palace last Thursday, when county staff presented the report and gathered input. “While that’s great on the one hand, it’s also hard because there’s no precedent to model our strategy on.”

The report is the latest resource put together by C-SMART’s stakeholder advisory committee, made up of representatives from Marin’s coastal communities, resource managers, utility providers, conservation scientists and other local and regional experts. Though it is not a planning document and does not address economic, social or environmental feasibility, it outlines adaptation options that the county has recognized as meriting further consideration. The manager for the project, Alex Westhoff, said all input will be taken into account for the production of the next draft, which will be presented to the Board of Supervisors on Aug. 1.

Attendees at last week’s meetings—another took place on Wednesday, at the Stinson Beach Community Center—were asked to rank next steps as high, medium or low priorities. (The survey is also available online.) Steps included developing both a homeowner’s guide to preparing for sea-level rise and technical guidance on home retrofitting; considering sea-level rise in capital improvement projects; establishing a citizens’ science monitoring program; and developing an interagency sea-level rise task force with agencies such as Caltrans, the National Park Service, PG&E and others. The options are based on a vulnerability assessment published by C-SMART in 2015.

That assessment found that at least 20 percent of buildings in the coastal zone are vulnerable, concentrated in the Calle and Patio neighborhoods of Stinson Beach, in downtown Bolinas, and along both shores of Tomales Bay.

Calle del Arroyo is the county road of most immediate concern, as it frequently floods and provides the only access to Seadrift, the Patios and many of the Calles. In Bolinas, many critical facilities and community resources are in harm’s way, including the grocery store, library, post office and school, and bluff-top homes may need to be removed once the edge erodes. In Marshall, the report says raising houses on the waterfront will be very difficult and expensive.

Overall, the vulnerability assessment found that nearly 20 miles of public and private roads could be compromised by flooding and permanent inundation. In the short term, Highway 1 between Bolinas and Stinson Beach, all the Calle and Patio streets, Wharf Road in Bolinas and several creek crossings and bridges are vulnerable; other low-lying portions of Highway 1, Sir Francis Drake Boulevard and local roads are vulnerable in the long term. Septic, sewage and water supply systems will also be vulnerable.

Residents are encouraged to reference the descriptions of vulnerabilities as well as adaptation strategies described for their specific community.

The report uses five different sea-level rise scenarios to explain near, medium and long-term strategies. The first scenario projects 10 inches of sea-level rise and an annual storm by 2030; the second near-term scenario assumes the same level of rise, but with a 20-year storm. Scenario three outlines 20 inches of rise and a 20-year storm by 2050. Long-term scenarios assume 40 inches and a 100-year storm by 2100, and 80 inches and a 100-year storm by 2100. 

“There’s a time component to all of this that makes prioritizing difficult,” Mr. Liebster said. “How do you do phasing so that if you focus on 20 years out, you can also be prepared for 30 years after that, taking into account funds, adapting regulations, environmental justice considerations…?”

The report suggests that in the near term, homeowners could elevate or otherwise retrofit structures to be safe from flooding in storms and high tides, and that the county can facilitate this through updated Local Coastal Program policies that build on the existing regulatory framework for flood hazard areas. (The exact framework is yet to be determined, as the county and the California Coastal Commission are now hotly debating the contents of the environmental hazards section of the amendments.) 

The county anticipates that property owners’ decisions will be heavily influenced by increased flood insurance rates and coastal armoring mitigation requirements. In the medium to long term, the report says homeowners will need to consider the tradeoffs of various adaptation approaches, and even decide whether to consider relocating to safer areas.

Road repairs may provide an opportunity to plan for higher water levels, the report suggests, though new design standards and best practices need to be developed. Permitting will be an ongoing challenge, as raising roads typically requires expanding the footprint and impacts natural areas. Additionally, agencies may evaluate the feasibility of relocating critical access roads upland. The report even suggests that specific stretches of road that are identified as being highly vulnerable to floodwaters could be converted into recreational trails.

Raising roads can be problematic for emergency access, as large vehicles can require a certain grade, the report states. Alternative evacuation routes need to be developed for communities, like Bolinas, with one major road that may face more frequent future flooding. Water-based emergency evacuation routes could be explored. 

Chris Choo, the county’s principal watershed planner, said it may be easy for the county to make emergency response its key strategy “because we have more regulatory freedom to repair what is broken, than to be preemptive.”

As utility systems become increasingly compromised by temporary—and eventually permanent—flooding, adaptation strategies include retrofitting water meter connections to withstand saltwater and retrofitting older septic systems to meet current regulations, or constructing flip switches for these systems that can be shut off during flooding.

Mr. Liebster emphasized how the Stinson Beach County Water District board, which the report states is retrofitting water meter connections to withstand saltwater corrosion, in particular has been at the forefront of sea-level rise preparedness. The report notes that protecting the Bolinas sewage treatment facility is a strong priority.

Working lands dedicated to agriculture and aquaculture will be primarily impacted by loss of road access; the report says the county should work with landowners to identify appropriate solutions. The second-generation Gospel Flat Farm “may eventually be conserved and returned to wetland,” the report says. 

Terry Sawyer, co-owner of Hog Island Oyster Company, said it is already difficult to acquire all the necessary permits when making any changes to such operations. Seated at a table focused on Marshall concerns at Thursday’s meeting, he said that “the projections of sea-level rise cannot be exact…and so as far as permitting goes, we won’t be able to abide by the status quo. We need faster adaptation—an emergency response team, for instance.”

As the basis for natural resource strategies identified in the report, the county referred to a report by a working group of the Greater Farallones National Marine Sanctuary. The report suggested the county and its partners continue to pursue funding opportunities for innovative living shoreline approaches such as dune and wetland restoration, horizontal levees, oyster beds, eelgrass and bluff vegetation.

In addition to the challenge of adopting regulations quickly enough, the cost of preparedness cannot be overstated. “How many zeros is that?” one Inverness resident asked last Thursday, squinting at the numbers projected on the wall during the county’s presentation.

The report includes cost estimates, with the caveat that they should only be used generally to understand relative costs from one strategy to another. While a seawall could cost $37,000,000 per kilometer and a tidal gate $200,000,000 likely in the Stinson and Bolinas areas, wetland enhancement throughout could be more like $20,000 per acre. Mr. Westhoff cautioned that the numbers could be much higher with the added costs of evaluation, design and monitoring projects. 

Nevertheless, Rhonda Kutter, a Point Reyes Station resident and aide to Supervisor Dennis Rodoni, had a positive outlook. “We have the opportunity as a community to demonstrate really creative thinking, to use the knowledge of the many engineers and architects who live here, and model a response to sea-level rise,” she said.