Bay Area governments could be required to demolish neighborhoods and take other measures to create shoreline buffer areas to allow the Bay to adapt to 14 inches of anticipated sea level rise over 50 years.
A state task force on Friday issued interim sea level rise projections that will guide planning efforts for all California agencies, including the Bay Conservation and Development Commission (BCDC), which governs construction and habitat management in the Bay and within 100 feet of its highest tides.
The Bay’s depth is influenced by seawater that spills into the waterway through the Golden Gate. As the Pacific Ocean rises due to climate change, Bay tides will rise and spread outwards to engulf land that currently remains generally dry.
Under the draft projections, California officials will prepare for a 14-inch sea level rise between 2000 and 2050. They will prepare for an additional 26-inch to 41-inch rise from 2050 to 2100.
The Bay rose eight inches over the past century, BCDC figures show.
Such severe projected rises could lead to widespread flooding in the Bay Area. They might be underestimates because they don’t account for potential “catastrophic ice melting,” the task force warned.
Under a long-running project, BCDC is proposing new rules and guidelines about building and other activities near the Bay, including a new finding that “landward marsh migration” may be necessary as sea levels rise.
“Appropriate buffers” around the Bay will need to be created or left undeveloped to enable marshes to migrate upwards, under proposed climate change-related amendments to the 42-year-old Bay Plan, which governs BCDC’s work.
“Some developed areas may be suitable for ecosystem restoration if existing development is removed to allow the Bay [to] migrate inland, although relocating communities is very costly and may result in the displacement of neighborhoods,” BCDC officials wrote in the proposed guidelines.
The agency is also proposing new shoreline protection measures, construction of flood-resilient or easily relocated buildings in vulnerable areas, demolition of existing structures, new risk assessment tools and incorporation of sea level rise projections into the agency's permit approval processes.
The proposed new guidelines could limit the amount of land that can be developed near the Bay, but they could also protect the region from widespread flooding in the coming decades.
As high tides rise, mud and other sediment that eroded from upstream rivers flows into the Bay and accumulates on shifting shorelines, replacing drowned habitat and providing natural defenses against floods. Such process can be disrupted by low sedimentation rates, shoreline topography and by the presence of buildings, roads and other facilities.
The flow of sediment into the Bay, which reached harmful levels after mud and other material was dislodged by now-banned mining practices in the Sierra Mountains during the 19th Century gold rush, could be running low.
The amount of sediment entering the Bay from the Sacramento and San Joaquin Delta is declining, according to the draft guidelines. “As a result, the importance of sediment from local watersheds as a source of sedimentation in tidal marshes is increasing,” the draft guidelines say.
The BCDC says scientific studies dealing with the issues of sediment flows into and around the Bay are needed.
A pilot project in Hayward seeks to protect low-lying electrical operations, a dump and water treatment facilities from rising seas by allowing naturally occurring sediment to build up the height of surrounding marshland.
“What we’re trying to do is to increase the height of the marshes in line with the sea level rise, and provide a steepening of the existing natural shoreline,” project consultant Jeremy Lowe told BCDC officials during a recent public meeting.
“The advantage of this is that we’re not continually having to go out and build up a levee and increase the height of it and put more rock on it. We’re hoping that such a system would allow the marsh to rise adaptively in response to changes in sea level rise,” Lowe said.
Roughly 60 local government representatives, land use attorneys and BCDC officials met in the agency's downtown offices on Friday afternoon to discuss the agency's proposed new guidelines.
Many of the concerns expressed by attendees related to the potential imposition of building rules upon local agencies within new areas by the BCDC.
BCDC Executive Director Will Travis said the agency would only impose building controls within its jurisdiction, which could only be broadened through the passage of new state legislation. Such legislation has not been proposed, he said.
The agency’s jurisdiction will, however, swell with the Bay as land becomes inundated by rising water levels, he said.
Guidelines affecting land outside the agency’s jurisdiction will serve as advisory policies.
Public hearings regarding the proposals are planned during regular commission meetings later this year, with plans finalized early next year, according to Travis.