Engineering Disciplines


Services

Seawalls, Revetments, Dikes & Levees

Reconstruction of Via Gaviota Seawall, Aptos, CA.

NCI assisted in the design and engineering of a curved parapet seawall of reinforced concrete and steel H-piling supports, fronted by a stone apron revetment of rock riprap, to replace a severely-damaged seawall for the Seascape Beach Association. Long-term protection and design criteria were based on the results of NCI's oceanographic analysis of design waves, water levels and beach erosion profiles.

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.

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Mandalay Bay Seawall Repair and Maintenance Bay Dredging Project, Oxnard, CA.

NCI performed a comprehensive condition survey of over 32,000 lineal feet of precast and cast-in-place concrete seawall. Design services included non-destructive and destructive testing to determine causes of deterioration; selection of repair materials and methodology; and preparation of construction drawings, specifications and cost estimates. A phased program of repair and preventative maintenance was developed. NCI's services also included full-time resident construction inspection and consultation. The City extended NCI's contract to prepare construction documents for additional phases of work. Professional underwater divers from NCI's sub-consultant Harbor Offshore, Inc. performed underwater surveys and investigations of the entire Mandalay Bay seawall foundation and slope protection areas. Over six miles of seawall were observed, logged, and compared to previous observations to assess existing condition and identify areas of needed repair.

Seadrift Revetment Shoreline Protection, Original Construction & Subsequent Repairs, Stinson Beach, CA

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.

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Hamilton Wetlands Restoration Project, Novato, CA.

NCI is the prime A/E contractor for a series of jobs for the San Francisco District Corps of Engineers on the Hamilton Wetland Restoration Project. This is a project to convert over 500 acres of a decommissioned army airfield to a wetland restoration area using dredged spoil material. The area will consist of seasonal and tidal wetlands. NCI has worked, or is working on 4 separate deliver orders under 2 separate IDIQ contracts. These consist of:

  1. Topographic mapping of the site using aerial photography, bathymetric surveys and land surveying to be used for planning, design and preparation of contract documents for design of all project features.
  2. Land surveying, geotechnical review, design, cost estimating and preparation of contract documents for the Bulge Levee and the Pacheco Pond Levee. These levees perform containment for a portion of the seasonal wetland. Design features included a ramp over the levee for construction and future access, tying into the existing Pacheco Pond Levee, using onsite borrow material, drainage, a road base, and demolition of existing facilities. MCACES was used to prepare the cost estimate. SPECSINTACT was used to develop the specifications. A SWPPP was prepared for the project.
  3. Additional design and preparation of contract documents for the N-1 Levee and Containment Berm to complete the perimeter of the seasonal wetland. Similar design services were provided for the Bulge Levee. Critical design issues included minimizing potential impact to an adjacent forced main sanitary sewer line. Both the Bulge Levee and N-1 Levee delivery orders were completed on an expedited schedule.
  4. Bathymetric surveying and numerical modeling to evaluate the effectiveness of and impacts from the wetland restoration project. This involved numerical simulations of hydrodynamics and sedimentation in the project area that includes both Novato Creek and the to-be-restored wetlands.

NCI is currently under contract with the Corps of Engineers (San Francisco District) to perform on-call design services for navigation and water resources projects. The largest design project to date is for the Hamilton Wetlands Restoration Project, which will be used as an upland dredged material disposal site until the restoration goals are achieved. This project involved the mapping (aerial topography, land surveying, and hydrographic surveying) of the site and surrounding areas and the detailed design and preparation of construction documents for two levees (3,240 feet long) to contain pumped-in dredged material. The owner is the California Coastal Conservancy, however the work was performed under contract to the San Francisco District Corps of Engineers. The work included evaluating potential onsite borrow areas, demolition of a hydraulic siphon system, design of a culvert through the levee for storm water flow, design of an access ramp over the levee suitable for construction equipment, connection to an existing levee, design of the levee cross-section to maintain clearance to the property line for a maintenance road and to provide a varying slope for aesthetics, and design of an aggregate base road surface. Quantity computations were performed, a SWPPP was prepared, SPECSINTACT was used to prepare contract specifications, and MCACES was used to prepare the engineer's cost estimate. The design project was completed under an expedited time schedule.

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San Rafael Ave Seawall Study, Belvedere, CA.  

NCI performed the necessary investigation and analysis in order to provide design recommendations with possible alternatives to prevent wind-driven waves from overtopping the existing approximately 2,000 lineal feet of stone revetment along San Rafael Avenue that fronts Richardson Bay within San Francisco Bay.

A topographic survey was conducted for the existing San Rafael Avenue seawall and the existing installation of the revetment was reviewed.  A coastal analysis was performed for the existing baseline condition, which included (1) determining return tidal stages, (2) estimating seal level rise, (3) wind-wave hindcasting and return frequency analysis of storm wave events, (4) computing wave runup using CEDAS, SPM method, CEM method, and FEMA model, and (5) determining the coastal flood elevations based on the return tidal stage, sea level rise and wave runup.  The design recommendations and potential seawall improvement alternatives were developed based on the engineering analysis.  In Addition, the design and construction costs for the potential alternatives were developed, and the regulatory permitting requirements and potential funding sources were identified.

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South Bay Salt Pond Restoration-Pond A8 Bridge & Weir Design, Alviso, CA.

The Pond A8 bridge and weir are an integral part of a restoration project to provide tidal flow between an historic salt pond and Alviso Slough.  The bridge is required to maintain access around the levee system after the channel through the levee is excavated.  The weir is required to control tidal exchange to obtain the design hydraulic conditions.

NCI was responsible for performing the detailed structural design and calculations, preparing construction drawings and special provisions, and preparing the Engineer’s construction cost estimate for these project components.  The structure consists of precast-prestressed concrete foundation piles and double Tee deck joists, cast-in-place concrete caps, floor, walls, deck and stop log columns, and an 8 bay adjustable stop log weir system.

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Broad Beach Seawall Repair, Malibu, CA. 

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.

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Potrero Power Plant Shoreline Stone Revetment, San Francisco, CA.

Engineering analysis and design services were provided in support of a shoreline interim remedial measure (IRM) which included a stone revetment on top a reactive core mat along a portion of the shoreline adjacent to the Potrero Power Plant in San Francisco, California. The shoreline IRM consisted of concrete debris removal and surface removal of the Manufactured Gas Plant (MGP) byproduct within the defined project area, and installation of a stone revetment over a reactive core mat, in order to stabilize the shoreline and enhance its appearance.

A coastal engineering analysis was conducted to develop the oceanographic design criteria for design of the revetment. The work performed in this analysis included: conducting statistic tidal stage analysis and determining return tidal stages; estimating sea level rise; conducting wind wave hindcasting and computing the wave conditions for different return frequencies; determining the revetment design parameters including the side slopes of the revetment, and the rock sizing and layer thickness for the armor layer and filter layer; and recommending construction methods and rock source. Engineering design services performed by NCI included: preparing permit design plans (grading plan & sections and revetment section details); producing the sediment erosion control and contingency plan draft specifications; preparing final construction drawings and specifications; performing final construction quantity takeoffs and cost estimate; evaluating construction schedule and methods; and providing construction support services during construction.

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