Highway 101 flooding solution in central Marin remains years away

The second in a series of five stories examining the major tidal flooding this month in Marin.

It was a Saturday, but drivers in central Marin were in gridlock.

Highway 101 at Lucky Drive was flooded, choking traffic in all directions around it. It would stay that way for nearly six hours on the busy post-holiday afternoon.

The low-lying, flood-prone area along the Corte Madera Creek — battered in the days leading up to Jan. 3 by torrential rain, winds and historic king tides — has been identified as one of Marin County’s most vulnerable locations to rising seas.

Constructing a defense is complicated.

The problem lies at the intersection of multiple jurisdictions and includes an array of decision makers, from municipalities to county government to the California Department of Transportation. And while high-level concepts to reduce flooding are described in plans, concrete proposals and cost estimates have yet to be established.

“The flooding happened where our study thought it would,” said Anne Richman, executive director of the Transportation Authority of Marin, the county’s transportation planning and financing agency.

“There’s not really any satisfaction in being right about that because obviously it had such large impacts,” Richman said. “We just look forward to continuing the work on it with our partners and trying to develop past this initial planning phase.”

Last year, the Transportation Authority of Marin adopted a sea-level rise adaptation plan that focuses on protecting the county’s highways and main transportation corridors. Approval enabled the agency’s staff to begin work with officials in the county’s 11 cities and towns to implement policy changes and start developing projects, including elevating roads and restoring marshlands.

For the area of Highway 101 at Lucky Drive, the plan proposes options such as levee construction along Corte Madera Creek and a tide gate. A third proposal involves elevating Highway 101 onto a viaduct or embankment, as well as raising Tamalpais Drive, Doherty Drive and Lucky Drive.

The plan proposes other strategies throughout the Corte Madera Creek watershed as well.

Richman said implementing any of those ideas, or others in the plan, would require greater community outreach, more intense planning and ongoing coordination among those in authority in the area.

“Marin has any number of overlapping jurisdictions, and coordination is difficult and may tend towards inefficiency rather than effective solutions and action,” said Supervisor Brian Colbert, whose District 2 includes Larkspur and the Ross Valley.

“The community is not interested in who’s got jurisdiction. They want to know how are we coming together to work for the common good,” he said. “We have to figure out, how do we pull together? That’s what the community wants.”

Marin County Supervisor Dennis Rodoni, whose District 4 includes parts of Corte Madera that were flooded, agreed.

“Caltrans is a major piece,” Rodoni said. “On top of that, there is all the water from the Corte Madera watershed, the creek drainage — it really needs to be a multiagency coordination and Caltrans needs to lead the discussion.”

The California Department of Transportation has launched a new study to take a closer look at vulnerabilities on the Highway 101 corridor from Sausalito to San Rafael, agency spokesperson Matt O’Donnell said. The project website is bit.ly/4bpFFPY. The agency plans to provide project information at an event in Marin City on Jan. 19.

The study, a $950,000 project expected to take two years to complete, uses the Transportation Authority of Marin’s adaptation plan as a foundation. The aim is to recommend sea-level rise adaptation projects to guide future investment, according to the state.

One of the focus areas is Highway 101 at Lucky Drive.

“Anyone who lives in Marin or commutes on that corridor knows really how vulnerable it is, and it will continue to be vulnerable to storm effects and sea-level rise,” said Supervisor Eric Lucan, the chair of the Transportation Authority of Marin board.

“The time to act, the urgency is now,” Lucan said. “That is exactly why in 2018, when we did the renewal of Measure AA, we set aside a portion of that revenue, which will account to over $8 million over the life of the measure, toward studying sea-level rise and adaptation planning to protect our infrastructure.”

The Measure AA sales tax measure allots 1% of its revenue, or around $250,000 annually, toward sea-level protection.

Marin County is facing about $17 billion in expenses to protect itself from about 2 feet of sea-level rise, according to regional agencies. Marin’s cities and towns are working to develop their own subregional adaptation plans to comply with Senate Bill 272. The law requires coastal communities to develop plans by 2034.

Areas of eastern Corte Madera are subsiding at a rate of more than 0.4 inches per year, largely because of sediment compaction, according to the report by the National Aeronautics and Space Administration. In the lowest areas, sea levels could rise more than 17 inches by 2050, more than double the estimated average of 7.4 inches for the region.

One problem is aging infrastructure, Colbert said. The flood control system in Corte Madera Creek in Kentfield, for example, was built in the 1960s, and impacts communities along the channel, he said.

“It can no longer handle the volume of water we’re seeing,” Colbert said.

The county has been pressuring the U.S. Army Corps of Engineers to modernize the system because of the increasing threat, he said.

Corte Madera has completed several studies to draft protections for its bayside neighborhoods, said Chris Good, the public works director. Town staff are now coordinating with Caltrans as it develops its plan.

“Unless a flood barrier is built around Corte Madera, Larkspur, unincorporated county and Caltrans land, tidal water will still be able to enter and potentially flood all four jurisdictions,” Good said.

“The main hurdles are the massive cost of building this type of flood barrier project and coordinating a project across several jurisdictions,” he said.

“This is why it’s so concerning that federal funding opportunities have really disappeared in the last year,” said Talia Smith, Marin County director of legislative and intergovernmental affairs.

“If last weekend’s flooding is any example, this is not a future scare, we’re contending with this now,” Smith said. “It takes years to get major grant applications ready, and when new grants come out, but the new administration comes in and kills them, it makes it really challenging to get shovel-ready projects funded.”

Voter approval of Measure AA, which extended the half-cent sales tax through 2049, is an important factor, Lucan said.

“TAM having our study and setting aside some of that local revenue helps us make the case for outside funding,” Lucan said. “It shows that we’ve done the legwork and signals to state and federal agencies that we’re prioritizing it.”