Bel Marin Levee Construction

The need for the Bel Marin Levee, near the Bel Marin Keys in Novato, CA, stemmed from flood risk management, environmental restoration, and community protection objectives. This levee construction project aimed to safeguard residential areas and infrastructure from potential flooding, particularly during storm events. Additionally, it was designed to enhance tidal wetland restoration efforts, promoting ecological balance and biodiversity in the region. By constructing the levee, the project sought to provide long-term resilience against rising sea levels and climate change impacts, ensuring the safety and well-being of the local community.
 
This massive heavy civil construction project was complicated by wildlife concerns, poor air quality caused by the 2020 California wildfires, the global coronavirus pandemic, and unanticipated soil conditions. Another challenge involved rerouting the Novato Sanitary District (NSD) outfall pipe, which serves as the primary discharge system for the City of Novato stormwater and sanitary treatment facility, having a very limited period in which the system could be shut down to facilitate construction. These challenges required close collaboration between the contractor, design engineer and owner.

Our team constructed the two-mile levee averaging over 275 feet wide and totaling more than 1.4 million cubic yards of engineered and compacted embankment fill, encompassing the construction of seasonal wetland ponds and an alkaline meadow to create more wetland habitat to support the natural ecosystem.

Our team used an array of equipment including tracked challengers and scraper cans, articulated haul trucks, bulldozers, excavators, compactors, tractors and discs, and water trucks to successfully excavate material from onsite borrow areas and placement as engineered fill material in the footprint of the levee.  In addition, soil was selectively removed and replaced within the seasonal wetlands and alkaline meadow to achieve necessary conditions to promote functionality and vegetation establishment. 

The project team worked closely with owner and onsite biologists to protect existing wildlife, including creating a buffer around an active bald eagle nest and other nesting birds, installing miles of exclusion barrier fence to protect the endangered marsh mouse and other protected species of wildlife.

The final phase of the project included rerouting and reinstalling a 63” pipeline and control vault for the NDS outfall system, which serves as a water control structure. This critical structure is designed to regulate water flow and manage water levels effectively within the system. The project team collaborated closely with the design engineer and NDS to redesign the system, ensuring it could accommodate changing conditions. The construction and tie-in to the existing system were successfully completed within a strictly regulated three-week shutdown period.

Led by the California Coastal Conservancy, the two-mile stretch of levee is the largest segment of the 2,600-acre Hamilton Wetlands Restoration Project on San Pablo Bay in Marin County. Once complete, the project will allow bay waters to eventually reclaim nearly 1,600 acres of former tidal marshes that had been diked and drained for agriculture and development during the late 19th and early 20th centuries.

The new levee is estimated to last about 50 years given current projections of sea-level rise but can be built higher should the California State Coastal Conservancy’s needs change. A local nonprofit organization was slated to replant the landscape, including 45 acres of native plants such as creeping wild rye, meadow sedge, and Baltic rush on the northwestern side of the levee.