Ocean Beach Shoreline Protection Great Highway Seawall
Ocean Beach, CA
NCI performed a comprehensive oceanographic investigation for 6,000 lineal feet of Ocean Beach, and provided planning and engineering services for the design of a major shoreline protection structure. Analysis included wave forecasting, littoral sediment transport, design water levels, beach erosion and sand replenishment. Alternative structural seawall configurations for various beach reaches were proposed, and then a physical hydraulic model investigation of these alternatives was performed by NCI to select a final seawall configuration and to finalize the engineering design criteria. The designed seawall was a modified O’ Shaughnessy structure consisting of a reinforced concrete upper section and stepped lower section, supported by concrete piles, and included cut-off piles at the structure’s toe. NCI also provided construction quantity take-offs and cost estimates. A beach monitoring and sand re-nourishment plan was developed to ensure that a minimum beach width is maintained.
NCI also provided coastal engineering peer review to the National Park Service for temporary shoreline protection prepared by the City of San Francisco for the eroding shoreline south of Sloat Blvd. The City of San Francisco had prepared plans to protect facilities south of Sloat Blvd. due to accelerated shoreline erosion. NCI reviewed available data and reports, and alternatives prepared by the City, and recommended modifications to the alternatives. Specifically, we evaluated alternative toe and crest elevation, armor rock and bedding layer size, structure slope, alignment, location and revetment length, and revetment flanks. Dune nourishment was also evaluated and a report of our peer review was submitted.
In addition, NCI analyzed and recommended procedures for placing sand on the beach that was excavated from the Oceanside Treatment Plant and the Lake Merced Transport System. The work involved the analysis of historical beach cross-sections, recommendation on proposed placement sections, and periodic construction observation. An analysis of beach nourishment was also performed as a potential shoreline protection method along Ocean Beach. This study was a result of comments and questions from the National Park Service and California Coastal Commission on the City plans for a seawall. Analysis included an evaluation of historical beach cross-sections, analysis of available sand sources generated from the Westside Transport System construction, and an analysis and costs of alternative sand sources.