Emergency Bridge Scour Countermeasure in Marin County, California, United States

Abstract

The Lucas Valley Road Bridge over Miller Creek in Marin County, California was identified as scour critical in August 2017. Within four months (just before the rainy season in California), structural, hydraulic, and monitoring countermeasures were installed at the bridge. Structural countermeasures included lowering the foundation at Pier 2. Hydraulic countermeasures included rock riprap around Piers 2 and 3 to inhibit local pier scour and a series of criss-cross weirs downstream to inhibit downstream head cutting. Monitoring countermeasures included a stage gage installation to monitor water surface elevation, a sonar device installation at the upstream and downstream ends of Pier 2 to monitor local pier scour and rock riprap movement, and sensitive tilt-meters to monitor movement of the bridge to give the local agency sufficient time to close the bridge prior to potential bridge collapse. This paper will focus on the case study of why the bridge is scour critical, and describe the countermeasures proposed to protect the safety of the travelling public.