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A concrete bridge in downtown San Anselmo upon which a heavily used public plaza has been located is unsafe and requires immediate repairs, Marin County public works officials said.

In a report submitted to the public works department on Sept. 12, Michael Watkins, one of several engineers the county hired to examine the bridge, wrote that the structure is at risk of “catastrophic failure.”

“If an earthquake occurs when a large activity is in progress on the deck,” Watkins wrote, “a structural collapse could occur which would result in many serious injuries.”

Watkins recommended that repairs be implemented as soon as possible. Otherwise, he wrote, “I recommend that the structure be declared unsafe and all activity on the structure terminated.”

On Thursday, county Public Works Director Rosemarie Gaglione said, “We’re planning on closing off the bridge in an abundance of caution.”

She said fencing, barricades and signs will be erected to keep people out of the area. The bridge spans San Anselmo Creek.

The structure, estimated to be between 80 and 120 years old, used to have a building on it with real estate and optometry offices, a restaurant and a salon. The building was removed in 2020 as part of a $20 million flood control project.

San Anselmo Councilman Brian Colbert said that since picnic tables and wood chips replaced the building, the area has become a popular community space.

“It’s become a gathering place, very much like Grand Central Station in New York City,” Colbert said. “You see people reading, working, just hanging out. It is in use from sun up to sun down.”

The flood control plan also called for the removal of the concrete bridge slab on which the building sat so the water in San Anselmo Creek could flow more freely. This would reduce the likelihood of flooding in the downtown and upstream.

That plan had to be put on hold, however. The Federal Emergency Management Agency has mandated the bridge must remain in place until work is completed to mitigate the additional flooding that the bridge’s removal would cause to about 20 downstream properties.

It is unclear how long county officials have been aware of the magnitude of the bridge’s structural damage.

At a meeting on July 19, Liz Lewis, water resources manager for the Marin County Flood Control and Water Conservation District, briefed county supervisors on the monkey wrench that the FEMA edict had thrown into the flood control plan.

Lewis’ presentation was part of a routine annual report on a storm water drainage fee that funds the effort. Lewis made no mention of concerns that the bridge might be unsafe.

Lewis, however, told supervisors that public works engineers were proposing to replace the bridge with a concrete baffle at a cost of $200,000. She didn’t make clear what that would accomplish, since the baffle would eventually have to be removed.

Lewis presented the same option to the San Anselmo Town Council on June 14, once again making no mention of any structural problems with the bridge.

Lewis did add, however, that if a decision was made to leave the bridge in place, liability for the bridge would be transferred back to San Anselmo. The county flood district purchased the structure for $1.75 million in 2018 as part of the flood control project.

The Independent Journal submitted a request to the public works department on July 25 requesting copies of any reports related to the safety and structural integrity of the bridge.

Gaglione said Thursday that it was after receiving the newspaper’s request that she received a final report from Martin/Martin Consulting Engineers outlining structural problems with the bridge and recommending repairs. She said soon after that the county hired MGE Engineering for a second opinion on the bridge’s condition.

Gaglione said the earlier suggestion to replace the bridge with a concrete baffle had nothing to do with concerns about the structure’s safety. She said the point of the baffle was to remove the bridge in time to access grant funding that is due to expire in June 2028.

Her department did not supply copies of the initial reports submitted by Martin/Martin and MGE Engineering. Instead, on Sept. 12, it shared a second report submitted by MGE Engineering on Sept. 9 and another evaluation submitted by Martin/Martin on Sept. 12.

The Martin/Martin report, however, indicates that the firm sent an analysis of the bridge to the county long before July 2022. It states that draft versions “were sent to the county for initial review on July 28 and August 16 in 2021.”

Gaglione said she never saw those drafts. She said neither Martin/Martin nor MGE Engineering could state with any degree of certainty how safe the bridge was because they had no information about its condition prior to repair work done in 2002, when the bridge was owned privately.

Gaglione said it was only after Watkins examined the bridge on Sept. 12 that she was able to verify that the bridge was unsafe. Watkins’ firm, Ballard and Watkins, oversaw the 2002 repair and provided a subsequent evaluation of the bridge to its private owner in 2006.

Watkins reported on Sept. 12 that “substantial horizontal cracking of the center wall had occurred since the previous repair projects were completed.”

Watkins wrote that the center wall of the bridge was bowing and that placed stress on the reinforcing steel within it.

“Should this steel yield, it is possible that the joint where the crack is visible at the center wall will unzip like a zipper,” he wrote. “This could lead to a catastrophic failure in this structure.”

“This discussion focuses on the effects of gravity on loads on this structure and has not yet introduced concerns of lateral loads which might be introduced during an earthquake,” Watkins wrote. “The degradation of this structure surely has resulted in the reduction of the ability to survive an earthquake.”

Gaglione said, “We’re still in talks with San Anselmo and FEMA about demolishing the bridge.”

She said repairing the bridge isn’t feasible due to the estimated cost and the uncertainty of the results.

Regarding repairs he recommended, Watkins wrote in a Sept. 13 letter to Gaglione, “There is no way to ensure that they will categorically eliminate the possibility of a collapse. The loss of life or injuries which might occur as a result of even a partial collapse during a community event would be difficult to justify.”

Gaglione said FEMA isn’t the only obstacle to removing the bridge.

“There are a series of events that would have to occur,” she said.

Gaglione said if it is possible to remove the bridge before Oct. 15, when the rainy season typically begins, something will have to be done to duplicate the bridge’s effect on the creek’s flow.

“If we take this bridge out,” Gaglione said, “we can’t just take it out and leave the waterway wide open because of those downstream properties.”

Doug Ryan, who has lived in a house downstream of the property for 18 years, said, “If they’re going to remove that bridge they need to do the mitigation that they’ve known they have to do for five years. They have already begun work in the creek, so if my house floods, I’m suing people. I’ve been very clear about that.”

Gaglione said it is too late in the season to replace the bridge with the concrete baffle. She said instead some large rocks covered with soil and netting might be used. She said the county has a hydrologist evaluating the possibilities.

If the bridge can’t be removed before Oct. 15, Gaglione said, the bridge will remain closed through the winter.

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