“I just finished reviewing the draft study of the parking lot flood abatement study and design and I wish to compliment you on the detail that went into preparing the document.”
Earl Johnson, Program Manager,
TERRA was retained by the U.S. Department of Transportation Maritime Administration (MARAD) to develop and evaluate alternative flood control measures for an at-grade equipment storage and parking area that supports the MARAD’s Reserve Fleet in Suisun Bay. This multi-acre site was created 30+ years ago by placing fill over the tidal marsh in Suisun Bay in an area that was underlain by a 100-foot thick layer of soft Bay Mud. Settlement of the fill over time caused the area to be subjected to frequent flooding because its elevation had become lower than the elevation of the water in the surrounding wetlands during periods of heavy rains and flood tides.
First, TERRA developed a state-of-the-art finite element model of the time rate of settlement of the site to assess the past and current rate of ground settlement at the site, and predict future settlement under various loading conditions. A number of potential solutions were considered for eliminating flooding of the area: a structural platform, raising site grades by filling with standard or light weight fill, a traditional perimeter flood wall/retaining wall, and an innovative lightweight concrete floodwall around the site in combination with minimal raising of the grade. This latter solution was the most economical and it also had the advantage that it maintained the limits of work within the footprint of the existing parking lot and avoided filling and environmental impacts to the surrounding tidal marsh.
TERRA was then retained again by MARAD to produce the final design and construction documents for the selected alternative and to provide construction-phase services. The plans, specifications (SPESCINTACT) and construction cost estimate were completed in January 2007. The construction of the flood wall and appurtenant structures was successfully completed in January 2008 and the wall has been performing well since then.