By the numbers: The anchorage basin dredging

$3.8 million

Project cost, federal funds.

402,000 cubic yards

Material to be removed.

32 feet

Dredging depth.

24-25 feet

Current depth.

Sources: U.S. Army Corps of Engineers, Charleston Branch Pilots Association.

MORRIS ISLAND — This old battleground is about to go up in flames again. But this time, it’s for shipping.

The U.S. Army Corps of Engineers plans to conduct managed burns in September in the dredging-disposal impoundment nearest to Cummings Point. The burns would clear the area to be used when an anchorage basin nearby is dredged later this year. The basin is used to anchor large commercial vessels.

The Army Corps announced its plans this week because the Cummings Point portion of the island is a historic focus and its beach is a weekend boating destination.

“We didn’t want the public to think Morris Island was on fire,” said David Warren, Army Corps project manager, adding that the burn has been scheduled for the month after the heavy summer boating season.

Morris Island is the low-slung, 840-acre barrier island at the southern tip of Charleston Harbor beyond Fort Sumter. Its northern edge, the 126-acre Cummings Point, is owned by the city of Charleston. It is the site of a legendary Civil War battle — an attack on Battery Wagner by the 54th Massachusetts Infantry Regiment, the first all-black unit — and is planned to be left as a passive park.

Two dredging-material impoundments lie between the point and the picturesque Morris Island lighthouse out in the inlet between the island and Folly Beach. Dredging materials were dumped there for a number of years before the Army Corps began disposing of them, primarily at an offshore site. The impoundments were last used in 2004.

The Army Corps also plans to move the impoundment walls, or dikes, back farther from the ocean. In 2010 the beach there was streaked orange, yellow and black from an apparent leak in the dikes, alarming Folly Beach residents. Army Corps engineers said it was natural stratification, or leaching of dredge materials, and some seepage of pluff mud displaced by the materials. But no tests had been run.

The Army Corps has now tested the length of the dikes for contaminants, Warren said. Organics and some metals were found, but in trace amounts, no more than would be found in someone’s yard. The dikes are being pulled back because of the relentless erosion of the island on that end, he said.

The island is losing as much as 20 feet of beach per year, an erosion rate that has left the lighthouse marooned in the inlet and has conservationists concerned that the island below Cummings Point might become an overwash beach within the next 50 years. An overwash beach is like a sandbar that goes underwater at high tide.

The erosion, ironically, is exacerbated by the Charleston jetties, built to protect the shipping channel.

The anchorage basin is a 157-acre span in Charleston Harbor along the shipping channel inland of Fort Sumter. It provides an area for ships to make repairs or be serviced without taking up cargo-loading space at the port, and as a “bailout” for ships in the channel that lose steering or power, said John Cameron, Charleston Branch Pilots Association executive director.

In 2006 the basin anchored an Egyptian freighter in legal difficulties that carried sailors without visas.

The basin last was dredged in 1992. It has since filled in and can no longer float 90 percent of ships that enter the harbor, Cameron said.

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