Rising seas and pounding storms taking toll on Highway 37

Surveying flooding along Highway 37 in January, ecologist Fraser Shilling began doubting his projections for when climate change will cause severe, perhaps catastrophic impacts on the major North Bay thoroughfare.

In an influential 2016 report used as a guide for the highway’s future, Shilling, co-director of the Road Ecology Center at UC Davis, had established a timetable of several decades for those impacts to be fully realized.

But that was before January storms forced the full or partial closure of the highway for roughly 12 days, causing havoc for thousands of daily commuters.

“We’re starting to overwhelm the system in places that we were thinking we had 20 years of lead time. But we don’t,” Shilling said this week from his office in Davis. Delaying action could be catastrophic, he said, predicting that one day water will push over embankments and levees and the highway will be “gone.”

Highway 37, one of the lowest-lying in California, has long been threatened by climate change and rising sea levels, inadequate levees and political waffling over who bears responsibility for maintaining and upgrading the road. The 21-mile highway meanders across four counties - Solano, Napa, Sonoma and Marin - traversing tidal marshlands, rivers and creeks, and farmland where flooding presents a threat to livelihoods.

“You’ve got farms, freeways and frustrated drivers - and sea level rise,” said Brian Swedberg, who manages 525-acre Petaluma River Farms north of the highway across from Port Sonoma.

According to Sonoma County historian Gaye Lebaron, Highway 37 dates to 1870 when the state Legislature passed a law allowing people to buy swampland for a dollar an acre contingent on the construction of levees.

Sections of the roadway were added in subsequent years, atop marshes at the edge of San Pablo Bay. A 10-mile section of the road was operated for a time as a toll road, prior to the state highway system purchasing that stretch in 1938 - the same year the Golden Gate Bridge opened.

Highway 37 afforded a more direct access to Vallejo from Sonoma and Marin counties. But flooding and sea level rise threaten to sever that link.

January floods forced Caltrans to shut the highway between Highway 101 and Atherton Avenue in Marin County for the better part of seven days, and to restrict traffic to a single direction an additional five days, according to California Highway Patrol data.

Roughly 41,000 vehicles pass through that stretch of highway on a daily basis, according to Caltrans.

As a result of the closures, motorists endured much longer drive times along detours that included residential neighborhoods.

“It’s no joke. This corridor is in peril. How do we address that going forward?” said Suzanne Smith, executive director of the Sonoma County Transportation Authority.

Swedberg, who has managed Petaluma River Farms for 30 years, said January’s “perfect storm” of heavy rain and high tides brought the river to within a half-foot of topping the levee protecting the farm. He said the river spilled over the levee in another location farther south, closer to the bay.

His perennial concern is that a major breach could overwhelm pumps and bring water gushing over sensitive farmland and the highway.

“It’s not going to get any better. That’s what Fraser tells us at all these meetings,” Swedberg said.

Indeed, the UC Davis ecologist said the January storms appear to be following a pattern of weather extremes that make planning and preparing for them a challenge.

“The swings are getting bigger and the pendulum is swinging faster,” he said. “That makes it harder to adapt.”

His research warned that Highway 37 could be regularly inundated by 2050 and fully underwater by 2100. Sea level has already risen by 8 inches along the California coast and by 2100 may be 36 to 66 inches above present levels, according to research cited in Shilling’s report.

January’s floods offered a glimpse of that future in the area of Novato Creek, which was ground zero for Highway 37 closures.

Dan McElhinney, chief district deputy director for Caltrans in the Bay Area, blamed the roadway flooding on a combination of factors, saying heavy rain, runoff from Stafford Lake and high tides swelled the creek beyond capacity and overflowed levees.

McElhinney cited several years when the highway flooded at that location, including 1996 when he said the impacts were felt for 18 days. But he said the flooding this year was unusual in that it appeared to be more heavily influenced by the tides.

The January storms struck during a period of exceptionally high tides along San Pablo Bay. McElhinney said there were moments when Caltrans crews had nowhere to pump the overflow because surrounding farmland and retention basins were inundated.

“You can only pump for so long,” said McElhinney, who presented his findings Thursday in Novato at a meeting of Highway 37 stakeholders.

Short-term, McElhinney said, Caltrans is exploring emergency upgrades to the highway near Novato Creek to try and minimize flooding. He said the work might include enlarging drainage pipes or elevating sections of roadway.

Longer-term, potential solutions include relocating the road to a causeway or a bridge between Highway 101 and Sears Point, or raising embankments along the highway.

SCTA’s Smith said preliminary cost estimates for the work range from $1.2 billion to $4.3 billion. To put that in perspective, $1.2 billion has been spent on widening Highway 101 since 2001, and the work is not yet done.

Using conventional state and highway funds, Smith predicted work on Highway 37 would not begin until 2088 - well after flooding is projected to become a routine problem.

“We need significant outside assistance, and that doesn’t exist at the state level, and it doesn’t really exist at the federal level, really,” Smith said.

Toll roads are another option. United Bridge Partners, a private investment firm with headquarters in Foster City, has proposed building a four-lane causeway between Sears Point and Vallejo, where there are now just two lanes, and to pay for the expansion using tolls.

But more than a year after the proposal was made public, the effort appears stalled.

“We’re in this dance where we keep going around in circles about trying to move forward,” said Sonoma County Supervisor David Rabbitt, whose district includes Highway 37.

A representative for United Bridge Partners did not return a message seeking comment.

You can reach Staff Writer Derek Moore at 707-521-5336 or derek.moore@pressdemocrat.com. On Twitter @deadlinederek.