A study by TAM, the Transportation Authority of Marin about rising sea levels has identified 19 areas of concern that are especially vulnerable to the effects of flooding from rising water.
“I think some of us have seen some of the storm impacts overlaying with king tides and know it’s really impactful,” said Mikaela Hiatt, a planner for the agency, according to the Marin Independent Journal.
The major areas of focus span much of the county, including Bel Marin Keys; Belvedere and Tiburon; Bolinas; the Hamilton Wetlands; Inverness; Marin City; Manzanita and Tamalpais Junction; Mill Valley, downtown and western Novato; Santa Venetia; Sausalito; Stinson Beach; Highway 37; Highway 101; San Rafael; Kentfield; Corte Madera; Terra Linda; and Larkspur. “They are mostly coastal areas, as expected, with some additional inland due to groundwater rise,” Hiatt said.
The technical study aims to find solutions to areas of transportation that are impacted by sea-level rise, and to help implement them. The 18-month study is being conducted by the Arup Group, a multinational design and planning company based in London.
TAM administers sales tax and vehicle registration fee collections through Measures AA and Measure B. The Measure AA sales tax measure allocates 1% — about $250,000 annually, according to Hiatt — of its revenue toward the sea-level rise program. Hiatt said there are also federal and state funding opportunities for projects on adapting to climate change.
As we reported previously, officials at every level of government are ramping up efforts to combat sea-level rise around the Manzanita Park and Ride, one of the most notoriously flood-prone sections of southern Marin that officials hope will get its own defense against sea-level rise.
Caltrans is proposing protections for the area along Richardson Bay between Marin City and Tamalpais Valley, namely the inclusion of the Manzanita Park and Ride lot and the Highway 101 interchanges at Shoreline Highway and Donahue Street.
“The goal of the project is to provide community protection and safe access in the face of near- and long-term sea-level rise in a way that does not degrade the sensitive habitat of the shoreline estuaries,” said Matt O’Donnell, a spokesperson for Caltrans. “The intent of this outreach is to incorporate public input early in the Caltrans’ project development process, to ensure project development is informed by the community in a transparent way.”
O’Donnell indicated that project planning is just getting started, and Caltrans officials have not decided on what will be proposed or a project budget. O’Donnell said planners are considering projects like elevating the infrastructure or raising the bayside Mill Valley-Sausalito bike path. Other options could involve repositioning parts of Shoreline Highway where it passes under Highway 101 to a higher elevation, he said.
A high-range cost estimate could be $200 million to $1.8 billion, depending on what strategies officials use, O’Donnell said.
Planners have not secured project funding, but it will be eligible for federal aid, O’Donnell said. A draft environmental document is expected to be disseminated for review in the summer of 2027.
“Reducing the duration and intensity of tidal flooding impacts at these specific locations would improve public safety and benefit the surrounding communities, such as Marin City, as well as the thousands of daily commuters and visitors in the area,” Kaelon said.
Marin County Supervisor Stephanie Moulton-Peters, who represents southern Marin, said she is grateful to Caltrans for making this project a priority. “This public meeting will be an opportunity for Caltrans to listen to the community, what we know about current local flooding and projected impacts of sea-level rise,” Moulton-Peters said.
In the meantime, Moulton-Peters hopes Caltrans will continue to work with her and county staffers to tackle short-term flooding in Marin City and Tam Valley.
“During a tour two years ago with Senator (Mike) McGuire, Caltrans identified short-term improvements to raise the roadway and improve drainage at Manzanita and Marin City,” she said. “We need Caltrans to improve the situation in the short term while they work on the long-term solutions.”