Army Corps plans annual dredging of Ninilchik harbor

On Friday, the U.S Army Corps of Engineers released a report about its annual dredging of approximately 9,000 cubic yards of material from Ninilchik’s small boat harbor, finding no expectations that it will impact the local environment.

Ninilchik’s small boat harbor consists of a mooring basin, designed to hold 32 boats (though sometimes holding up to 100, according to the Army Corps report), in the mouth of the Ninilchik River just upstream of where it drains into Cook Inlet. A 50 foot-wide channel, with a depth of 9 feet above the average lowest tidal line, leads from the basin into the Inlet and is passable at high tide. The harbor is used by recreational boaters and commercial fishermen, most of whom deposit their catch at canneries in Kenai, according to the report.

The flow of the Ninilchik River and the currents of Cook Inlet fill the harbor basin and channel mouth with sand, silt, and gravel. To preserve the harbor, the Army Corps has been dredging it annually since it was built in 1961.

The dredgings considered in the report — those between 2017 and 2019 — are planned to follow the Corps’ usual procedure: material removed from the harbor will be trucked to a temporary basin on the Ninilchik beach and stored while its water drains back into Cook Inlet. After it’s dried out, the dredged material is used to build up eroding areas of Ninilchik’s shoreline.

One change in the future dredging procedure will be its volume. Future dredging will remove an additional 4,000 cubic yards of material because of an update from the National Oceanic Atmospheric Administration that predicts a change in local tides.

With the increase, the Ninilchik operation’s volume will be comparable to the approximately 15,000 cubic yards the Army Corps dredges annually from Homer’s small boat dock and adds to the Homer Spit. Both are dwarfed, however, by the approximately 1 million cubic yards of material the Army Corps dredges from the Port of Anchorage between April and November, according to the report.

Until 1996, the Corps put the dredged matter to the north of the harbor mouth. However, researchers discovered that the local Cook Inlet current flows predominantly south during the winter and was carrying the material back into the harbor. Subsequently, it has been deposited to the south of the harbor mouth instead.

The report released Friday considered deposit locations on the both the north and south beaches. The Army Corps’ preferred option would spread the material along erosion-prone areas of the south beach, giving some to the Alaska Department of Transportation, which since 2013 has used up to 5,000 cubic yards of dredged matter to shore up roadbed revetments and maintain its own erosion-control project.

The environmental assessment cites studies that analyzed dredged material from the Ninilchik harbor for signs of contamination, concluding that no significant contamination was found. The report states that most small boat harbors have “low-level chronic contamination,” but material from the Ninilchik harbor may be cleaner because the harbor is flushed out by the river, the report authors speculated.

Materials tested for include diesel, lubricating oil, metals from fuels, paint, and batteries, pesticides, and solvents. Only arsenic and chromium were found in the sediments in levels that exceeded the Alaska Department of Environmental Conservation’s standards for disposal, but “were determined to be within background concentrations and are assumed to be naturally occurring,” the report stated.

The timing of the dredging work — between March 15 and May 15 — is designed not to interfere with the area’s spawning populations of chinook, coho, and pink salmon, nor with steelhead and Dolly Varden trout. The timing is also meant to avoid the period in which larval razor clams settle into Cook Inlet’s coastal mud.

The Army Corps study considered impact to birds, fisheries, water quality, and the endangered populations of beluga whales, Steller sea lions, and Steller’s eider. Regarding water quality, the authors concluded the dredging “would generate a short term degradation of water quality in the nearshore environment of Cook Inlet” but that “no adverse impacts would result because of the inherently high background turbidity levels in Cook Inlet.”

Most of the minimal environmental impact considered in the Army Corps report would to be to seafloor invertebrates. The shoreline of Ninilchik lies within the Alaska Department of Fish and Game’s Clam Gulch Critical habitat area, a 30,000-acre coastal strip between Kasilof and Happy Valley managed to preserve habitat of razor clams, a species harvested for food. However, harvests have declined since 2011 and the Alaska Department of Fish and Game has closed east side Cook Inlet beaches to clamming since 2014. In a previous Clarion interview, Fish and Game biologist Carol Kerkvliet said the causes are still unclear.

The dredging itself would kill any clams that may have settled recently in the mooring basin and channel, but the report authors don’t expect dispersal of the dredged material to affect clams due to precautions the Army Corps plans to take, according to the report.

Concluding that most clam habitat is in the lower intertidal region, the report states the Corps will deposit material more than ten feet above the average low tide line. In the area around the high tide line, the depth of deposited material will be limited to a foot or less. The report states that “this narrowed-down area is not associated with high quality razor clam habitat.”

The Army Corps of Engineers has no public meetings planned on the action, but will take comments by mail and email until October 16.

Reach Ben Boettger at ben.boettger@peninsulaclarion.com.

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