One of Sonoma Valley’s key backroad links is officially offline. The narrow Watmaugh Road bridge over Sonoma Creek, just south of Sonoma Plaza, is now closed for demolition and replacement and is expected to remain closed through the summer of 2027. Work kicked off in mid-June, and county crews have rolled out a signed detour that funnels local traffic around the work zone. The move cuts a heavily used route for commuters, school traffic and agricultural vehicles, and it is likely to tack extra minutes onto a lot of daily drives.
According to The Sonoma Index‑Tribune, Sonoma County Public Infrastructure announced the closure and laid out a detour that sends drivers north on Arnold Drive, east on Leveroni Road and south on Broadway before reconnecting with Watmaugh Road. County staff told the paper they expect the crossing to remain closed through summer 2027 while crews remove the old span and construct a new two-lane bridge.
Contract and funding
County documents show Viking Construction Company came in as the low bidder on March 11 with a base bid of $7,112,953. With a 20% contingency, the contract’s not-to-exceed amount is $8,535,543.60. Sonoma County also notes that roughly 88.5% of the project cost is expected to be reimbursed through the Federal Highway Bridge Program.
Timeline and environmental safeguards
Permitting documents spell out a tight construction window in the creek itself. All in-water work must be wrapped within a single season, from June 15 through Oct. 15. Crews will set up a temporary gravel work pad and dewater a portion of Sonoma Creek to isolate the construction area. CEQAnet, the state’s CEQA portal, details required mitigation measures and a performance security tied to potential impacts on endangered California freshwater shrimp.
Detours and daily impacts
Sonoma County’s road evaluation report pegs average daily traffic at about 3,955 vehicles on the stretch of Watmaugh Road between Arnold Drive and Highway 116. That figure highlights how many drivers will now be pushed onto the detour. With only a single crossing closed, the impacts will still be felt most by school routes, local delivery trucks and farm vehicles that relied on the shortcut, and county staff are warning motorists to expect delays while construction is underway.
A bridge with a long history
The existing steel truss bridge dates back to 1929 and has attracted attention from historic bridge researchers even as engineers have flagged it for seismic and safety upgrades. Preserving a detailed record of the structure while planning its replacement has been on the county’s to-do list for years. Archival surveys and county historic reports document the bridge’s late 1920s origins, and HistoricBridges.org provides additional background on the span’s design and history.
What officials say
County leaders are pitching the project as an overdue safety upgrade for a critical valley connection. Replacing the bridge is essential to ensuring the safety, reliability, and resilience of a critical connection in Sonoma Valley, Rebecca Hermosillo said in a statement to The Sonoma Index‑Tribune, which reported that the county expects most of the costs to be covered by federal reimbursable funds.
