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Posted 4/16/2012

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By Sean McBride
Charleston District Public Affairs

Recently, the United States’ largest trailing suction hopper dredge, the Glenn Edwards, spent several weeks in the Charleston Harbor entrance channel performing maintenance dredging. The Glenn Edwards collected more than 1.5 million cubic yards of sediment during her time in Charleston, ensuring that the entrance channel remains at its federally authorized depth of 47 feet.


A hopper dredge is capable of dredging material from the harbor floor, storing it onboard the ship and eventually transporting it to the disposal site where it is dumped. The Glenn Edwards has two large arms that come down, suck up material off the harbor floor, and bring it to the center part of the ship. When the ship is full, the ship moves to the ocean dredge material disposal site (ODMDS) and opens the doors on the bottom of the ship, releasing the material back into the ocean.


How often does a hopper dredge have to make trips to the ODMDS? That depends on how much material the ship can hold. A standard hopper dredge tends to hold a few thousand cubic yards of material per load. The Glenn Edwards can hold up to 13,500 cubic yards of material. Since the Glenn Edwards can hold so much more material, this makes the process more efficient and less costly.


While maintaining optimum efficiency, the dredge team is also charged with keeping watch for endangered species. Dredge companies that have contracts with the Charleston District must have an observer on their ship that monitors endangered species life. During each dredging cycle, the wildlife observer is looking to see if any whales are in the area. If they are, the dredge ship must slow down and take precaution. After each dump cycle, the observer checks to see if the ship caught any endangered turtles. Most often, there are minimal issues with encountering endangered species, but if dredging operations do encounter one, there is protocol that must be followed during the next cycle.


Economically, hosting the crew of the Glenn Edwards in Charleston also brings numerous fiscal benefits to the city. During its time in Charleston, the Glenn Edwards fills its 200,000 gallon tank with gas at local stations and the 18 man crew spends approximately $4,000-6,000 weekly on groceries from local stores.


While the Glenn Edwards can hold a large capacity of dredged material, this is not the type of dredge that would be used in a harbor deepening. This type of dredge specializes in maintenance dredging and beach renourishment as it is not as effective when digging into new material.


The Charleston District is charged with maintaining the federally authorized depths of 45 ft in the harbor and 47 ft in the entrance channel. To do this, a dredging cycle is utilized consisting of dredging the entrance channel every 24 months, the lower harbor every 12-15 months, and the upper harbor every 18-21 months. The Charleston District’s maintenance of the harbor began more than 130 years ago and will continue strong into the future.

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