USA: Marsh Island Dredging Provides Flood Risk Reduction Benefits

Marsh Island Dredging Provides Flood Risk Reduction Benefits

As construction workers maneuver bulldozers and spread sand to restore the degrading marsh island, Yellow Bar Hassock in Jamaica Bay, N.Y., their work is being closely observed by an area resident.

For the past few months we’ve seen him on the site. He just keeps doing his thing,” said Melissa Alvarez, a Senior Project Biologist with the U.S. Army Corps of Engineers New York District.

The resident Alvarez is referring to is a Harbor Seal who has been seen lying on the dredge pipeline that is delivering the sand and sunning himself as the U.S. Army Corps of Engineers performs its work. “I find it so amazing every time we construct one of these island projects how quickly wildlife will use this area.”

This has been the case with the prior marsh islands the Army corps has restored in Jamaica Bay and is showing to be the case with Yellow Bar Hassock that was completed by this summer.

Yellow Bar Hassock is part of a marsh island complex located within the 26-square mile Jamaica Bay Park and Wildlife Refuge that was the country’s first national urban park and one of the Gateway National Recreation Areas.

The refuge is located in an urban area that includes portions of Brooklyn, Queens, and Nassau Counties, N.Y. The area’s shorelines are boarded by heavily developed lands including John F. Kennedy International Airport, the Belt Parkway and several landfills.

For over the past century, the Jamaica Bay marsh islands have been disappearing at a rapid rate. Since 1924 nearly 80 percent of the islands have disappeared. They are disappearing at a rate of approximately 44 acres per year and more in the last decade.

It’s believed that a great deal of this degradation is due to regional urbanization.

If something is not done to stop this loss, it’s estimated that the marsh islands could vanish by 2025, leaving wildlife homeless and threatening the bay’s shoreline.

According to Alvarez, a certified professional wetlands scientist, maintaining the health of these marsh islands is critical to the wellbeing of wildlife and the 20 million people that live and work in this urban region.

The marsh islands are home for a variety of wildlife, including fish and shellfish which are an important food source for birds and help improve water quality by removing things like nitrogen and phosphates,” said Alvarez.

She continued, “These islands also serve as flood protection and shoreline erosion control for the bay’s surrounding homes and businesses. They dissipate wave energy, minimize storm surge and provide flood risk reduction benefits.

For the public, this means less erosion to personal property, more species available for recreational fisheries, better water quality, and preservation of the Gateway National Recreation Area that is visited by millions of people each year.

For the past decade, the Army corps in partnership with other agencies has restored 180-acres of marsh in Jamaica Bay, including Elders East and Elders West marsh islands and Gerritsen Creek.

The Army corps is working with the Port Authority of New York and New Jersey, National Park Service (Gateway), New York City Department of Environmental Protection, New York State Department of Environmental Conservation, National Resources Conservation Service, and the New York/New Jersey Harbor Estuary Program.

To restore Yellow Bar Hassock marsh island, 375,000 cubic yards of dredged sand was pumped on the island and shaped to simulate the proper elevations of a marsh island. This work added an additional 42 acres to the degraded island, restoring it to a 156-acre habitat.

The sand placed on the island was dredged and beneficially used from the Ambrose Channel, part of the Army corps’ New York/New Jersey Harbor Deepening Project. In the past, this sand would have been dumped into the ocean, so this program is a win-win for the environment and taxpayers.

They then planted seed on nearly 30 acres of marsh. The team collected the seed from within Jamaica Bay.

The low marsh areas were seeded with smooth cordgrass. This plant is a natural anchor for the marsh sediment and can tolerate salt and low tides. In the high elevations of the marsh they planted over 100,000 2-inch plugs of saltmarsh meadow grass and spikegrass. These plants are less tolerant of salt, but endure the salt water during the moon high tides. These plants were also collected within Jamaica Bay.

Before the sand was placed, the team removed 11,000 hummocks from the marsh island’s low lying areas. Hummocks are mounds of terrain and vegetation above ground that are often made from decaying plants. In this case, they’re made up of native smooth cordgrass.

The team stored the hummocks in fenced off areas on the project site and after the sand was placed on the island they transplanted them onto the new areas of higher elevation.

Hummocks are a natural anchor for the marsh sediment because they are part of the historic marsh which are already matured and will fill in to stabilize the island.

Lisa Baron, U.S. Army corps of Engineers New York District program manager added, “The other marsh islands we restored look incredibly vibrant and healthy. One could only hope that’s the way the other marsh islands will end up, including Black Wall and Rulers Bar Hassock marsh islands that the Army corps is going to begin working on in August.”

Yellow Bar Hassock is already beginning to look good. Alvarez says that she’s spotted Horseshoe crabs laying eggs on the island. Horseshoe crabs haven’t been seen in the area and just a year ago this island wasn’t suitable for them because it was a barren mudflat. Alvarez said, “The old adage of ‘Build it and they will come’ suits Jamaica Bay’s islands and specifically Yellow Bar Hassock very well.”


Dredging Today Staff, June 22, 2012; Image: usace