The Sonoma County Board of Supervisors on Tuesday took charge of a proposal to replace a historic steel-truss bridge near Sonoma, despite objections that the move is intended to fast-track the project without adequate public input.

The project involves Watmaugh Bridge, built in 1929 to span Sonoma Creek and connect what is today Arnold Drive with Highway 12 leading into Sonoma.

County officials want to replace the bridge with a new one, saying the span is at risk of collapse during an earthquake or major flood because of erosion around the piers that support it.

Preservationists contend the risks have been inflated and are seeking to have the bridge rehabilitated.

On Tuesday, supervisors unanimously supported invoking a protocol known as "original jurisdiction" that gives them direct authority over environmental review of the bridge project, thus circumventing the county planning commission.

Supervisors did not comment on the action, which was part of their consent calendar.

Tom O'Kane, the county's deputy director of public works, said his office requested the oversight change to speed up the process, and not because he feared planners might kill the project.

He said the public has had ample time to weigh in on the details. "My Lord, we've had 2? years of public input," he said.

But Nancy Simpson, Sonoma Valley's designee to the county Landmarks Commission, told supervisors Tuesday that the public has been promised "that there will be many steps to this process."

Sonoma resident Gail Johnson read a letter from former city Planning Commissioner Patricia Daffurn, who called the board's move "appalling" and wrote that it "prevents an objective and thorough review" of the project by an outside body.

The Landmarks Commission previously recommended that a replacement bridge not be built because of the potential effects on the span's historical character and because alternatives have not been fully explored.

But county staff say the state and federal funds available to do the work are tied to building a new span, which they estimate will cost $4 million to $5 million.

Supervisors in August voted unanimously to award a $500,000 design contract on work for the bridge to Moffatt and Nichol, a global engineering firm based in Long Beach. In addition to replacing the span, the firm will study alternatives, including a retrofit or building a parallel bridge downstream.

O'Kane said the public will have another opportunity to weigh in on the project Oct. 16 when supervisors are tentatively scheduled to discuss the impact of the proposed work on the environment under the state California Environmental Quality Act.

Staff Writer Brett Wilkison contributed to this report.

You can reach Staff Writer Derek Moore at 521-5336 or On Twitter @deadlinederek.