Old Santa Cruz Highway Culvert Repair

The Project, located approximately 0.2 miles east of Highway 17 and south of Lexington Reservoir in Los Gatos, California, addresses critical infrastructure failure caused by a landslide during the 2022/2023 winter storms, which compromised an exposed culvert outlet downstream of the highway and triggered severe bank erosion along Arroyo Mocho Creek. This ephemeral creek, a headwater tributary feeding into Lexington Reservoir and ultimately the Guadalupe River watershed, requires immediate stabilization to restore proper drainage and protect public safety. The remedy involves extending the culvert outfall down the steep hillside to a less gradient slope and reinforcing it with rock riprap to dissipate energy and prevent scour. The extended culvert will reroute and dewater the section of the creek between the original outfall and the new downstream point, mitigating further erosion and ensuring flow continuity toward the reservoir. To restore the highway’s structural integrity, the project includes the construction of a soil nail and micro pile-supported shotcrete wall to reclaim the roadway width and provide a four-foot shoulder necessary for guardrail installation. Controlled Low Strength Material will be used as backfill between the stabilized slide face and the wall to ensure structural support, while the toe of the wall will be reinforced against undermining by stabilizing shallow landslide materials. Additional measures such as a pinned mesh apron and horizontal drains will manage subsurface seepage below the wall. The culvert outfall and its downstream flow path will require enhanced scour protection through targeted armoring to safeguard against future erosion from storm events. The project is being coordinated under the jurisdiction of the Regional Water Quality Control Board, Region 2 – San Francisco Bay, with oversight focused on protecting water quality and watershed health throughout the Guadalupe River system.