With the finish line clearly in sight, the U.S. Army Corps of Engineers San Francisco District is working to complete the final construction phases of the Hamilton Wetland Restoration Project in time for next year’s tidal breach.
"We anticipate breaching at the beginning of next year," said Robin Liffmann, Hamilton project manager. "We’re seeing the light at the end of the tunnel, and that’s really exciting."
Formerly a U.S. Army airfield, Hamilton is a 988-acre site near Novato, Calif., and one of the largest wetland restoration projects on the West Coast. A decade in the making, the project aims to create a complex landscape of seasonal and tidal wetlands, as well as a multi-purpose trail for public access.
One of the key components to restoring wetlands is dredged material, or mud. It serves as the foundation for building the kind of typography conducive for growing plants and attracting wildlife. To date, the Corps has placed approximately six million cubic yards of dredged material at Hamilton for beneficial reuse, much of it coming from the district’s Oakland Harbor Navigation Improvement Project, which deepened the nation’s fifth largest port from a depth of minus-42 feet to -50 feet in 2009.
"We are essentially using the mud to raise the elevation of the site, which would have happened naturally if we breached it, but it would take decades longer," said Eric Jolliffe, Hamilton environmental planner. "This is a critical area for a couple of endangered species—the salt marsh harvest mouse and the [California] clapper rail— so there’s an advantage to creating this site as fast as a possible."
With the mud in place, the Corps has focused much of its current construction efforts on contouring the site using backhoes and bulldozers in order to create a network of channels, ponds and islands.
"You have ponds that stay inundated during certain times of the season for various types of birds," said Liffmann.
Work is also being done to finish a wildlife corridor that will serve as a pathway for wildlife moving between the bay fringe and the upland areas of the site.
"The corridor will be 300-feet wide with a very gradual slope, almost imperceptible, to maximize the area of transition between wetland and upland," said Jolliffe. "This transition is a rare type of habitat, and there will be a whole series of plants that grow just in this zone."
Biologists for the Corps have been propagating most of these native plants—such as oak, buckeye, coyote bush and snowberry—on site since the opening of a large-scale plant nursery last year at what was formerly a water treatment facility. With time being critical, a nursery in close proximity to the project allows biologists to grow native plants and get them in the ground quickly.
"You avoid an invasion of plants you really don’t want," said Liffmann. "The point is to set it up with the plants you want, so it will be sustainable in the future."
Helping this effort has not only been the Corps and its two partner agencies— the California State Coastal Conservancy and the San Francisco Bay Conservation and Development Commission—but local volunteers.
"The nursery is one of the hubs of the project," said Liffmann. "People definitely want to come visit and see what’s going on out there."
Breaching the site to tidal action is also expected to be a major event sure to attract the crowds. Quite simply, the process involves cutting down the site’s outboard levee to the level of the marsh plain and creating a channel cut to allow the bay tides to flow in and out of the site unimpeded. It will be the last step toward restoring the level of hydrology that existed at Hamilton more than a century ago.
"If we had just breached the levee and let nature take its course, the estimate was 50 years before it would start forming what we’re creating now," said Liffmann. "In this respect, we’re helping nature along."