Marin County delays demolition of San Anselmo bridge

Marin County officials have delayed plans to demolish a deteriorating bridge in San Anselmo until 2024.

The decision has raised hopes on the San Anselmo Town Council that the bridge could be reopened as a plaza in the meantime.

“I requested and received our council’s support for the town of San Anselmo’s staff to explore the costs and necessary steps for us to reopen the plaza,” Councilmember Brian Colbert said Wednesday.

The county closed the bridge in September, saying it is structurally unsound and poses a danger to the public. Members of the San Anselmo council believe the bridge could be repaired at a reasonable cost and used safely, at least temporarily.

During a presentation to the Ross Town Council on March 9, Marin County public works managers said it no longer appears feasible to tear down the structure commonly known as Building Bridge Two this year as previously planned.

The meeting took place at the request of the Ross council, which asked to be updated on flood control efforts in the Ross Valley. Public works officials were scheduled to meet with the San Anselmo council on Tuesday to provide a similar briefing, but canceled at the last minute.

Colbert said he and San Anselmo Councilmember Alexis Fineman have been meeting with representatives of the county to forge an agreement to reopen the bridge as a plaza. Colbert said the council wants to put the platform to use until it is demolished.

Colbert said the county “gave us a tentative no” on March 6.

“They’re not going to reopen the plaza,” he said.

The bridge, estimated to be 80 to 120 years old, has become the focus of two controversies. One involves San Anselmo residents who want to continue using the structure as a platform for a plaza. The other is based on concerns that the structure’s removal will increase the risk of flooding for at least 20 homeowners in Ross and San Anselmo.

“We have joined a concerned citizens’ group and are organizing to fight the demolition of Building Bridge Two,” Diana Davis of San Anselmo said during the public portion of the Ross council meeting.

Jeff Kroot, who served four terms on the San Anselmo council, said, “The people overwhelmingly support keeping this plaza.”

Removing Building Bridge Two has become the linchpin of the San Anselmo Flood Risk Reduction Project. The Marin County Flood Control and Water Conservation District purchased the bridge in 2018 with the intention of tearing it down. The bridge’s removal would allow San Anselmo Creek to flow more freely, thus reducing the likelihood of flooding in the downtown and upstream areas.

Initially, the flood project called for the creation of five floodwater detention ponds, including one in San Anselmo’s Memorial Park. Because of opposition from neighbors and other factors, only one pond — at the former site of the Sunnyside Nursery growing ground in Fairfax — has been built.

An environmental impact report prepared for the flood project in 2018 determined it would increase flooding at 20 parcels during 25- and 100-year floods. The same report determined that the project would reduce flooding at 635 parcels during a 25-year event and 480 parcels during a 100-year event.

The findings have blocked the county from moving forward with the project because the Federal Emergency Management Agency prohibits any work that would increase flooding before mitigations have been completed.

At the March 9 meeting, several property owners expressed frustration that the county still has not told them what mitigation it plans for their properties.

“It’s been very hard and unfair to our residents to live with this project for so long without being told what the mitigation is,” said Ross Councilmember Elizabeth Brekhus.

Brekhus noted that if the owners of the 20 properties decide to sell, they would have to disclose that there is a “cloud” hanging over their parcels.

Berenice Davidson, a county public works official, said the county hopes to begin conversations with the 20 property owners within the next two months. But Davidson said first the county must meet with FEMA to supply it with updated flood modeling from the environmental impact report.

Davidson said the county’s model is more accurate than FEMA’s because it incorporates the effects of drainage systems outside San Anselmo Creek. FEMA’s model was used to determine its flood insurance rate maps that became effective in 2017.

Davidson said that when the county meets with the property owners, they will be shown an illustration of how the base flood elevation is expected to change relative to the first floor of their homes.

“Based on how that changes, it is going to dictate the type of mitigation that we would be proposing,” Davidson said.

At the meeting, several property owners objected to the suggestion that no mitigations would be forthcoming for increased flooding below the first floor.

“There are a lot of people who have their mechanical, electrical and their duct work all under that finished floor,” said Charles Goodman. “We have to come up with some way of mitigating that. It’s a problem.”

Samantha Hobart of Ross said, “I don’t want there to be water underneath my home. It lessens the structural integrity of the home and it increases risk.”

Completing mitigations isn’t the only task public works staffers must finish before demolishing the bridge. They must also create an addendum to the environmental impact report to reflect design changes for the creek bank adjacent to the bridge, and for the fact that several other bridges in the watershed that were expected to have been removed by now still remain.

Last year, the public works office considered tearing down Building Bridge Two and replacing it with a $200,000 concrete baffle that would duplicate the bridge’s effect on water flow to avoid increased flooding downstream.

Davidson said the baffle was contemplated because a grant that will help pay for the bridge’s removal was due to expire at the end of 2022. Since then, she said, the county has secured an extension of the grant until the end of 2024.

“Therefore,” Davidson said, “we believe we can take down the bridge after mitigations without having to spend funds on installing the baffle.”