Daly City Emergency Landslide Repair

City of Daly City

City of Daly City

Year Completed:



The project is located in Avalon Canyon on a steep bluff on the Pacific Ocean.  The 30-inch diameter CMP carrying 80 cubic feet per second (36,000 gallons per minute) of stormwater flows failed.  During the many storms that followed the initial pipe break, water flow from the pipe caused additional headward erosion, while unusually heavy rainfall caused discharge of large volumes of water at high velocities onto the unprotected soils.  Approximately 120,000± cubic yards of material was removed by landslide and erosion.

Design concepts and construction documents were required to be prepared and released for bid within a one month period of the design team being retained.  Oasis’ work effort consisted of close coordination with Jacobs Associates, review of the engineer’s drawings, development of criteria and subsequent recommendations for slope protection, tree planting, winter monitoring, maintenance and repair, and preparation of a Storm Water pollution Prevention Plan to satisfy the Regional Water Quality Control Board requirements and on-site construction administration.

The project ultimately consisted of cut and fill of 430,000 cubic yards of soil, installation of subsurface drainage systems, rehabilitation of 550 lineal feet of storm drain, installation of 1,800 feet of storm drain pipe, installation of the “canyon drainage system” (corrugated aluminum pipe, ditch drains, sediment basins, rock rip-rap revetment at the ocean front), and provision of erosion control and re-vegetation for the canyon slopes.  Monitoring and maintaining the reconstructed canyon slopes continued through the 1999 rainy season.