San Ramon Canyon Stormwater Flood Reduction Project

Residents, commuters and emergency response teams used to dread winter rainstorms in Rancho Palos Verdes. Water and debris would regularly flood a major roadway and undercut other roads adjacent to San Ramon Canyon. Flash floods and erosion had produced 30-foot-deep cuts that produced landslides in the canyon walls, threatening homes downstream and a nearby sewer line.

The Harris team developed a much-needed stabilization and stormwater flood reduction project, which provided safety and peace of mind to the city and its citizens.

Harris delivered design services for the largest single project undertaken by the city. Floodwaters were re-routed and the eroding canyon walls—which were encroaching on the roadway about five feet every year—were stabilized. A storm drain inlet structure and two tunnels diverted water under roads and through solid bedrock for more than three-quarters of a mile to a new outlet at the base of a 150-foot-high coastal bluff.

Harris was hands on throughout the project’s design and also provided construction-related support services to ensure success for the city. Harris’ design eliminated the threat of losing roads into the canyon, eliminated flooding of the roadway at the canyon mouth and stabilized the canyon walls—all while providing 100-year flood protection to downstream neighborhoods.

Core Elements

The $16 million in project improvements included:

• A large inlet structure in the canyon and a steel pipe from the inlet structure to a beach below the bluff
• A steeply sloped tunnel to the beach and large outlet structure on the beach
• Partial filling of the canyon with a gravity buttress and a rock-lined canyon invert downstream of the inlet structure
• Reshaping and re-vegetation of the canyon slopes
• One temporary and one permanent access road for construction and maintenance

Beyond the Blueprints

Harris did its homework and came prepared: We developed the project concept during the proposal phase and ensured its exact execution during construction. Harris also provided the city with a project study and preliminary design, evaluating six alternatives, which ultimately came full circle and confirmed Harris’ original concept. Harris also directed all of the professional surveying and geotechnical and environmental components.

The quality of the study and our proposal work led the city to trust Harris with the planning, specifications and estimate phase