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Restoring an eelgrass habitat after 70 years

The availability of clean dredged material from the deepening of the shipping channels presented an opportunity to restore Oakland's Middle Harbor as a shallow water marine habitat.

Mott MacDonald performed numerical modeling to help recreate 45 acres of eelgrass as part of a 90-acre ecological reserve.

Award

2011 Outstanding Environmental Project of the Year, American Society of Civil Engineers San Francisco Section

Opportunity

The Port of Oakland’s Middle Harbor was a shallow tidal marsh until it was dredged during World War II to accommodate ships docking at the Naval Supply Depot. The 190-acre (77-hectare) Middle Harbor has been dredged continuously since then, making it up to 40 feet (12 meters) deep at low tide. The greater depth made it unproductive as habitat.

In the 1990s, the Port of Oakland realized that shipping channels elsewhere in the bay had to be deepened to ensure that Oakland remained could handle larger ships and remain competitive with other West Coast ports. Dredging was authorized by the Federal Water Resources Development Act of 1999.

The availability of clean dredged material from the deepening of the shipping channels presented an opportunity to restore the Middle Harbor as a shallow water marine habitat while providing nearby, cost-effective placement of the dredged material.

Solution

In 1998, the US Army Corps of Engineers retained Mott MacDonald to perform numerical modeling for its Middle Harbor Habitat Project, intended to recreate approximately 45 acres (18 hectares) of eelgrass as part of a 90-acre (36-hectare) ecological reserve including deep water, shallow water, and shoreline habitats.

The project consisted of dredged material placement, rock and sheet pile containment structures, tidal channels, and avian roosting islands designed to provide protection from wave action and enhance circulation within the habitat area.

Our engineers performed services including the following:

  • Numerically modeled tide-induced currents and sediment transport
  • Collected current and wave data
  • Developed a model to optimize eelgrass habitat survival and enhance tidal circulation
  • Provided wave information for design of roosting islands and containment structures
  • Designed public access beach at the northeast corner of Middle Harbor
  • Simulated storm-induced beach profile evolution to predict erosion of the beach fill during storms

Outcome

Mott MacDonald has contributed to the efforts of the Sierra Club, Audubon Society, Save San Francisco Bay, and other organizations through a Technical Advisory Committee process to restore the tidal marsh and wildlife habitat of Middle Harbor.

The placed dredged material is still undergoing settlement with beds of eelgrass to be transplanted to the site in the coming years to provide habitat for small fish, an important food source for the endangered Least Tern.

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