Posted on April 1, 2021
The Charleston Harbor will be the deepest harbor on the East Coast at 52 feet once the Post 45 Charleston Harbor Deepening Project is complete.
Currently, there are a record number of dredges in the harbor in order to complete the $600 million project by the end of 2022. Typically, two or three maintenance dredges are moving material to allow ships to pass easily through the harbor, but the project has increased dredge activity to about 10 dredges.
At the end of the project, 40 million cubic yards of material will be removed, which is equivalent to filling 12,000 Olympic swimming, pools.
Jeff Livasy, the civil works chief for the project with the U.S. Army Corps of Engineers, compares the deepening project to a more iconic infrastructure project: the Ravenel Bridge that connects downtown Charleston to Mount Pleasant.
“It’s fulfilling the same purpose because that bridge needed to be elevated to allow for bigger ships to pass under it and our harbor needs to be deepened to allow bigger ships to sail through the harbor,” Livasy said.
The ability of larger ships to go in and out of the harbor will allow more goods and products to reach the port in one trip. As a result, those savings will benefit consumers in stores and buyers of manufactured goods.
“The Post 45 Charleston Harbor deepening project is all about transportation efficiencies,” said Livasy.
With funding from the South Carolina Ports Authority and the federal government, the project, which began in 2010, will be completed in 12 years, which is “quite a big accomplishment,” according to Livasy. The federal benefit-cost ratio is 6.4, so for every dollar invested, 6.4 dollars is returned to the economy of South Carolina and the country.
On a daily basis, there are 250 workers with 51 pieces of equipment removing $600,000 worth of material.
There are several different types of dredges used to complete the project as efficiently as possible, said Livasy. At the entrance channel of the Charleston Harbor, hopper dredges pull up the material, hold it inside the ship as it sails offshore to a placement site to empty the material.
For those driving across the Ravenel Bridge, they will primarily see clamshell dredges in the lower harbor. These dredges look like cranes as they pull the material off the bottom of the ocean, put it into a barge and place the material offshore.
The offshore placement site, known as the Ocean Dredged Material Disposal Site (ODMDS), is approximately 10 miles offshore past the jetties. The ODMDS existed prior to the project for maintenance dredging, but was expanded to fulfill the needs of the deepening project. Livasy described the ODMDS as an underwater containment area.
In the upper harbor at the Hugh K. Leatherman Terminal and the North Charleston Terminal, cutterhead suction dredges are used. These dredges move the material directly by agitating it with a rotating cutterhead, which is able to cut through hard material. It mixes the material with water and deposits it in an upland placement site, which is located under the I-526 bridge between Daniel Island and North Charleston.
After the project’s completion, maintenance dredging will still occur yearly because the material naturally accumulates over time.
The Charleston Harbor has been deepened seven times since 1852 when it was first deepened to 17 feet. The most recent deepening was in 1996 to 45 feet. The main reason to continue deepening the harbor is due to increasing ship sizes.
Last fall, the 1,200-foot long CMA CGM Brazil was the largest ship to go through Charleston Harbor, but with its almost 37-foot draught it was only able to do so because it could ride the tides. When the deepening project is complete, there won’t be restrictions on ships similar in size to the Brazil.
A certain portion of the dredge material will be deposited at Crab Bank, the manmade island at the entrance of Shem Creek which acts as a bird rookery. The material that is dredged near Crab Bank is compatible for beach habitat because it has more sand content compared to the more typical silty material. Another cutterhead suction dredge will be brought in to move the material to Crab Bank in the fall.
