‘SLOW-MOVING EMERGENCY’
Marin report on sea-level rise shows community-by-community impact of near- to long-term worst-case scenarios
Editor’s note: This article, the first of a two-part series, first appeared in the May 3, 2017, edition of The Ark. It earned second place for In-Depth Reporting in the California Newspaper Publishers Association’s 2017 California Journalism Awards contest.
By GRETCHEN LANG
glang@thearknewspaper.com
Blackie’s Pasture, local ferry facilities and Tiburon’s waterfront under nearly 13 feet of water. Stormy seas that sweep over downtown Tiburon, flooding the fire station, Town Hall, the library and the post office. Belvedere Lagoon and Paradise Cay homes destroyed by flood damage. A new report released by Marin County paints a grim picture of the possible effects of rising sea levels on the Tiburon Peninsula.
The draft Marin Bay Shoreline Sea-Level Rise Vulnerability Assessment, prepared by the county’s Department of Public Works and Community Development Agency, marks out Southern Marin communities like Tiburon, Belvedere and Strawberry as being particularly vulnerable to the effects of higher tides and storm surges over the next 60 years.
But by the end of the century, many parts of the county as a whole will be at risk, according to the report. More than 12,000 homes, businesses and institutions, hundreds of miles of roadway and vital infrastructure like sewage treatment plants, transit centers and fire and police stations could be inundated at high tide, impacting more than 200,000 residents and commuting workers. Damage estimates run into the billions of dollars.
Click to read Part 2 of 2: ‘Belvedere faces sea-rise issues head-on’
“This is a slow-moving emergency that needs our attention now,” said Chris Choo, program manager of the county’s Public Works Department and principal planner on the project.
The assessment is part of the county’s Bay Waterfront Adaption and Vulnerability Evaluation, or BayWAVE, program, which began in 2015 with funding from the county and a $250,000 grant from the California Coastal Conservancy. It is a joint effort between county municipalities, local, state and federal agencies and elected officials from local jurisdictions.
Among them, Belvedere Councilmember Claire McAuliffe sat on the executive and policy committees alongside Kate Sears, the county’s Southern Marin supervisor, whose region includes Strawberry and Tiburon. Tiburon Councilmember Alice Fredericks was also on the policy committee, while the town’s community development director, Scott Anderson, sat on the technical advisory committee with former Belvedere City Manager Mary Neilan.
The report uses map data to catalogue what businesses, homes, infrastructure and natural resources are vulnerable to sea-level rise throughout the county.
“This builds a foundation for understanding and planning for sea-level rise adaptation,” officials wrote in a press release accompanying the report.
According to the assessment, by the end of the century, reductions in usable space for living, tourism and transportation could impact some 12,750 properties and 100 miles of roads.
Based on damage estimates using the Federal Emergency Management Agency’s Hazus tool — hazard-analysis software developed and distributed by the agency — wind, waves and temporary flooding could account for $60 million to $6 billion in damages. Access to the county could be increasingly compromised by flooding along Highways 101 and 580, and vulnerable low-income neighborhoods like San Rafael’s Canal area would flood.
Homes and roads built on filled bay mud could subside as the ground below them saturates with water.
Sea-level rise may also combine with typical hazards of the region such as earthquake liquefaction, erosion of soils and heavy rainfall.
“Marin is more vulnerable than this assessment can describe,” the report says.
Rising tides
San Francisco Bay waters have risen 8 inches in the past century, and they could rise by nearly 70 inches by the end of the century, according to a 2012 National Research Council report “Sea-Level Rise for the Coasts of California, Oregon and Washington.”
But the exact level of sea-level rise over the next century is hard to predict, scientists say, depending on variables such as melting polar ice and global warming due to greenhouse-gas emissions. Projections by the National Research Council range widely, from just 1.6 inches to 11.8 inches in the next 15 years.
By 2100, the rise could be anywhere from 16.6 inches to 65.8 inches — a dramatic range that makes realistic or likely predictions difficult to pinpoint.
Choo said the researchers chose numbers at the higher end of the ranges to match other research being done in West Marin. Residents there wanted a “worst-case scenario” look at the possibilities of sea-level rise, she said.
Marin planners chose to look at six different possible scenarios — 15-year, mid-century and end-of-century expectations — starting with a projected 10 inches of rise in 15 years and then adding the effects of a 100-year storm surge in each alternative scenario. The medium term considers 20 inches of ocean rise and the long-year term 5 feet of rise, each with second 100-year-storm-surge scenarios.
The scenarios selected are derived from the U.S. Geological Survey Coastal Storm Modeling System, which combines global climate and wave models with projected sea-level rise.
In the near term, with 10 inches of sea-level rise, seasonal high tides could routinely flood bayfront Tiburon, including Point Tiburon homes and businesses and Shoreline Park, the ferry facilities, and the Old Rail Trail; and in Belvedere, low-lying Corinthian Island homes, West Shore Road and Beach Road homes and the San Francisco and Corinthian yacht clubs. In unincorporated areas, regular flooding at Paradise Cay and Greenwood Cove would be exacerbated.
If a hundred-year storm occurs, an additional 3,000 acres of land could flood countywide. Ferry service across Marin could be compromised by high tides, and boats in harbors could be damaged by storm surges.
Over time, marshlands, which currently act as a buffer against storm surge, could start to degrade, transitioning from high marsh to low marsh and then to mud flats and open water, the report says.
By the end of the century, with a proposed 60 inches of sea-level rise, tidal flooding could reach far along the Richardson Bay shoreline into Mill Valley.
Locally, along with Tiburon Town Hall, the fire station and Belvedere-Tiburon Library, flooding could reach The Cove Shopping Center and Belvedere’s Community Center — which includes City Hall and the Police Department — as well as the Strawberry Village Shopping Center and homes along Strawberry’s Seminary Drive and Harbor Point.
Across the county, a possible 12,100 homes, businesses and institutions totaling $15.6 billion could be at risk, the report states. Just in Tiburon and Belvedere, the risk is to nearly 900 homes totaling $2 billion.
“These are impacts that can cripple our economy,” Choo said. “It’s a big deal and we need to be planning for this. It’s part of our responsibility.”
Impact on Tiburon
While many Tiburon residential properties sit in the hills and are safe from the danger of sea-level rise, some 341 homes, including apartments and condos, and more than 8,500 people would be vulnerable under the long-term, worst-case scenario, which includes 5 feet of sea rise and a 100-year storm event. In that scenario, FEMA’s hazard-software estimates $187 million in damage in 2016 dollars if all vulnerable buildings were destroyed by such an event.
Homes on the peninsula’s bluffs would be hit hardest, with docks and other water features wiped out first.
Tiburon’s commercial areas wouldn’t fare any better. As much as 65 percent of commercial buildings in the town could be vulnerable to flooding by the end of the century, the report states. That includes Main Street shops and restaurants, downtown hotels and the Boardwalk and Cove shopping centers.
Ten percent of commercial properties face flooding in the 15-year scenario. Historic buildings on the bay side of Main Street could flood with 7–9 feet of water at high tide. By the end of the century, nearly 100 buildings in Tiburon could flood with 3 feet of water at high tide, including the fire station and post office, library and Town Hall.
Infrastructure and transportation would also be affected. By the end of the century, 1.5 miles of roadway would routinely flood including Beach Road, Main Street, Juanita Lane, Blackie’s Pasture Road and parts of Paradise Drive. Add a 100-year storm and Tiburon Boulevard would flood, potentially cutting off the entire peninsula to ground-based help from the outside.
Underground electric and sewer lines could be damaged by rising ground water. Seawater will increasingly back up into manholes, already a common problem at the intersection of Beach Road and Tiburon Boulevard, causing further flooding.
Tiburon Town Manager Greg Chanis called the analysis exhaustive and sobering, and he encouraged all town citizens to read it.
“It is difficult to dismiss the fact that the bay has risen 8 inches in the last 100 years,” he said, “and by all indications it’s going to continue to rise. It would be short-sighted to ignore it.”
Chanis said the town will incorporate the affects of sea-level rise into its capital projects budgets and prioritize projects that will address sea-level rise. Storm drains and roads will be the first priority, he said.
One of the projects that is on the town’s to-do list is a pump to address the flooding at the intersection of Beach Road and Tiburon Boulevard, he said. When high tides occur during a major storm, waves push the flap at the end of the drain closed and stormwater backs up through manholes.
“With rising tides, we would expect that to happen more over time,” he said.
Homes vulnerable in Belvedere
McAuliffe, the Belvedere councilmember, also characterized sea-level rise a “slow-moving emergency” for the Tiburon Peninsula and said it is vital to cooperate with other agencies and jurisdictions to share knowledge and resources.
“It’s so potentially impactful on so many levels,” McAuliffe said. “Pursuing a common goal is the right thing to do.”
She said Belvedere is pursuing grant money to study the seawall along Beach Road and the breakwater along San Rafael Avenue, both areas of potential risk in the long term.
In a city with few businesses but a significant number of low-lying homes, the worst-case scenario, of 5 feet of rise and a 100-year storm, the study shows an impact on 550 homes, including apartments and condos, and more than 2,000 people. If nothing is done to stop rising seas or protect from them, officials projects more than $356 million in damage in such an event if vulnerable buildings were destroyed — a figure that assumes the lagoon’s tidal gate is stuck open during a powerful storm surge.
Even on the near term, with 10 inches of sea rise, some 47 buildings face flooding of as much as 6 feet during tidal flooding. The most vulnerable homes are along the lagoon and on West Shore and Beach roads. If Beach Road and San Rafael Avenue are compromised, the community would be isolated from Tiburon — including from the fire station.
Unincorporated Tiburon and Strawberry
On the backside of unincorporated Tiburon, along San Francisco Bay, one area of particular concern is Paradise Cay — the development off Paradise Drive built on fill in San Pablo Bay.
By the end of the century, the community “could be completely lost to sea-level rise, with more than 70 percent of the parcels compromised by … tidal flooding in the long-term,” says the report.
“Storm surges could do significant damage before sea-level rise takes full affect.”
With flooding, the community would be cut off from land-based emergency services.
The beach at Paradise Beach Park could also disappear, and Sanitary District №5’s Paradise Cove treatment plant would be vulnerable under a worst-case scenario of 5 feet of rise and a 100-year storm. Official estimates are more than $123 million in damage to 290 destroyed buildings in that scenario.
Meanwhile, low-lying parts of Strawberry will be vulnerable from the near to long terms, including commercial areas along the Redwood Highway frontage road, such as Strawberry Village and other retail and restaurants, as well as the gas stations farther south.
Highway 101 off-ramps, which already experience seasonal flooding, would see further tidal impacts. Long-term storm-surge flooding could be seen along Seminary, De Silva Island and Strawberry drives, along with Strawberry Circle and the Redwood Highway frontage road. Brickyard Cove and Strawberry Point Park, along with Aramburu Island, would flood out, as would many Marin and Golden Gate Transit bus stops and Strawberry Point Elementary School.
Though classified in the report as being part of Strawberry, residential properties along Greenwood Cove in unincorporated Tiburon would see flooding in the near term, along with Westminster Presbyterian Church and Strawberry Preschool.
Under the worst-case, long-term scenario of 5 feet of rise and a 100-year storm, the community has 279 vulnerable buildings, with officials estimating some $214 million in storm-damage if they’re destroyed.
Community workshops
Last week, the county held one of three community outreach meetings at the Mill Valley Community Center, hoping to involve local citizens in possible future solutions to sea-level rise.
Residents and staff played “Game of Floods,” a board game created by county planners to help citizens understand the challenges of flood control. Players act as planning commissioners challenged to develop a 2050 vision for a hypothetical Marin Island.
Roger Leventhal, a flood engineer in the Public Works Department, talked of the various solutions to rising seas used around the world, including levees and dikes, building flood-proof buildings on stilts and “managed retreat” — or abandoning buildings that are too close to the shoreline. Most of those solutions are problematic and expensive, he pointed out.
Marin is exploring a more progressive solution, he said, in engineered beaches or “living shorelines” that will block wave action and prevent shoreline erosion. Leventhal recently created one such beach on Aramburu Island off Strawberry Point and hopes to create more, he said. But, in the end, Leventhal told the crowd, a combination of solutions will probably have to be used to combat rising seas.
Choo, the county planner, also encouraged the crowd to contact the county with ideas and concerns about sea-level rise.
“There’s a lot to do, but there’s a lot we can do if we start planning now,” she said.
Contributing writer Gretchen Lang of Belvedere covers the environment. She spent 15 years abroad writing for newspapers including the Boston Globe and the International Herald Tribune.
Click to read Part 2 of 2: ‘Belvedere faces sea-rise issues head-on’
