In 1997 a 160 feet long seawall was constructed in front of four properties at the western end of Broad Beach, Malibu in order to protect these homes during periods of high storm waves occurring during extreme high tides and severe beach erosion. The seawall consists of drilled in-place steel pipe piles extending into hard bedrock that supports epoxy coated steel sheet piles driven into an upper silty-clay formation that underlies the beach sand deposits. In addition, a reinforced concrete cap covers the upper portion of the steel sheet piles down to the top of the steel pipe piles. NCI has performed routine inspection of this seawall over the years, and during that time has observed the gradual increase in corrosion to the steel structural components of this seawall. In 2008 NCI prepared a detailed report addressing the application of potential protective coatings for the maintenance of this seawall.

Then after the occurrence of high storm waves during extreme high tides and beach erosion in January 2010, NCI recommended the urgent need in proceeding with the necessary repairs to this seawall. After the preparation of the construction repair plans, specifications and contract documents, and in securing all necessary regulatory permits, the construction repairs consisted of removing all steel corrosion, applying an externally bonded fiber reinforced polymer strengthening system, extending the seawall return walls further landward, performing epoxy injection and mortar repairs to the concrete, and improving drainage and backfill on the seawall’s landward side. Repair work was completed in July 2010.

During the midst of the 1983 storm waves, NCI provided emergency engineering design, plans and full-time construction inspection for the placement of over 35,000 tons of rock riprap along 7,500 lineal feet of shoreline for the protection of 125 property owners and residences. Close cooperation between NCI, the client and the contractor prevented the loss of any residence. This structure was constructed to a 2.5:1 (horizontal: vertical) slope with a toe elevation of approximately +7 feet MLLW (Mean Lower Low Water) and a crest elevation of +17.5 feet MLLW. Prior to 1983, an emergency revetment structure was constructed during the winter season of 1978 along the western portion of the existing structure and in 1980 along the eastern portion. This emergency structure on the eastern portion consisted of first installing sand-filled geotextile Longard tubes and then placing stone directly behind the Longard tubes.

Since the emergency placement of this revetment in 1983, NCI has provided ongoing beach monitoring surveys and inspection of the revetment to assess beach impacts, as well as services for final regulatory permit acceptance. Additionally, during 1998, NCI performed a detailed inspection/evaluation of the entire seawall structure, and based on this evaluation, recommended the placement of 5,500 tons of new stone on a lot-by-lot basis for stone that had settled/dislodged during the previous 15 years. NCI then prepared the construction contract documents, secured regulatory agency approvals, performed contractor bidding and award/negotiation of contract, and provided full time resident inspection and construction management during placement of this additional stone. Also, in 2004 and 2006 NCI again provided the same services for the placement of 3,000 tons of new stone during 2004 and the placement of 700 tons of new stone repair work during 2006. Since 1985, NCI has continued to provide either annual or bi-annual inspections/evaluations and to recommend additional repair work as necessary.

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.