San Rafael, CA – About three weeks of repairs to Lucas Valley Road Bridge over Miller Creek, located between Mount Lassen Drive and Huckleberry Road in unincorporated San Rafael, began December 7. The bridge and creek fortification project, overseen by the Marin County Department of Public Works (DPW), may cause delays as a result of short periods of alternating traffic but will remain open at all times for the duration of the project.
The Lucas Valley Road Bridge over Miller Creek underwent a thorough evaluation before repairs started on December 7.The project was designed by Biggs Cardosa & Associates and the repair work is being handled by Maggiora & Ghilotti, Inc. Funding for the estimated $400,000 project comes from the County’s Road & Bridge Fund and DPW is pursuing grant opportunities for reimbursement.
The California Department of Transportation (Caltrans), which is in charge of annually inspecting bridges in Marin, found that the foundation of Lucas Valley Road Bridge, and the surrounding creek bed were damaged during the January 2017 storms. In May, Caltrans notified DPW of the need to conduct detailed analysis of the bridge’s integrity. Although some scour (sediment erosion) had been identified after the winter storms, given that the bridge’s foundations are subterranean, the impact to the structural integrity could not simply be visually determined. DPW initiated two sequential investigation efforts covering civil, structural, geotechnical and hydrological engineering analysis.
Results showed pervasive creek erosion at several locations along the creek bed and around the bridge’s foundation. Additionally, the creek bank has experienced head-cutting, which is the deterioration and receding of the creek channel. Because of the extent of scouring and potential strain on the bridge’s foundations, it was necessary to fix the bridge immediately to avoid significant damage from future severe storms, including potential closure of the bridge. The design process and repair work was expedited for the sake of public safety.
Miller Creek is a passage for steelhead trout during the winter months. In line with the County’s ongoing effort to protect riparian habitats, DPW has worked with Biggs Cardosa & Associates, which has extensive experience in fish passage development. The project implements an array of best practices to minimize the impact to steelhead trout during the project. Staff has been coordinating with the National Marine Fisheries Service, the Regional Water Quality Control Board, the Army Corps of Engineers and the California Department of Fish and Wildlife to review and assist in matters related to the steelhead trout migration.
The reinforcement of the creek bed will require removal of sediment from 50 feet upstream to 100 downstream from the bridge. Grading of the creek bed will be conducted to improve water flow control and assist fish passage. Boulders, some weighing upward of two tons, will be positioned on the bed in place of the removed sediment along with an Engineered Streambed material to prevent future scouring. The foundations of the bridge itself will be reinforced with concrete and steel.
During construction, the water will be diverted around the project site using two 24-inch diameter pipes. If a large storm occurs during the project, temporary bypass pumps have been reserved to manage the increased water flow.