Maintenance dredging at the Port of Redwood City channel is done every two to four years to keep the channel at a depth of minus 30 feet, allowing ships to enter, Port director Michael Giari said.
"What is unique is that for the fist time the sediments dredged from the channel are being place on Bair Island to restore the tidal marsh," Giari said of the new project. "It has never been done before here in Redwood City."
Giari said the project is being done by the U.S. Army Corps of Engineers, which awarded a $3.6 million contract to DDM Crane & Rigging to move sediment from the bottom of the port channel into barges. The barges will be towed up Redwood Creek to a pumping station, where the sediment will be removed to be piped to Bair Island. The process will take about five or six weeks, Giari said.
Sediment will be used on a 35-acre portion of Bair Island, which is a 3,000-acre portion of the Don Edwards San Francisco Bay National Wildlife Refuge. The U.S. Fish and Wildlife Service is under control of restoring about 1,400 acres of the island to tidal wetlands, according to the city of Redwood City.
Fish and Wildlife Services has created levees around the 35-acre portion of the island, and sediment dredged from the Port of Redwood City will be piped into the levied area, Giari said. The sediment is about half water and half mud, and when the liquid separates mud will be left to raise the land level.
When the levees are breached for the area to be restored to marshland, the mud will have restored the area to a level between high tide and low tide -- the level of a more natural tidal wetland, Giari said.
"Then you have an area subject to tidal action," he said.
Plants will then begin to grow and the marsh will be restored in a process expected to take three to four years.
"There has to be more work done than just placing the dredge mud," Giari said. "We may have some more dredge material to put there in the future, but this was the first time."
In the past, sediment dredged from channels in the Bay Area has been dumped in deepwater sites in the bay, Giari said. Encouragement from agencies to cut down on the amount of dredged material placed in the bay lead to the cooperation between the Port and the restoration of Bair Island, with the help of numerous public and private agencies, according to Giari.
"It was a matter of a number of agencies realizing that this would be of benefit to everyone to do it this way," he said.
Information about the restoration of Bair Island is available online from the city of Redwood City at www.redwoodcity.org.