A Different Catch: Charleston District Innovates to Speed Post-45 Study

Charleston District
Published June 10, 2013

It is a beautiful sunny day in the quaint fishing village of McClellanville, SC. The moss is blowing in
the majestic oak trees that lead up to the picturesque dock where the Miss Georgia shrimp boat is rocking back and forth in the wind. On the dock, dogs are excitedly running to and fro; a pelican is waiting on a dock post; a dolphin keeps poking her head out of the water checking on the shrimp boat’s status; all of them seem to know that the activity aboard meansthe boat will be pulling off soon.
All of the sudden, the Charleston District’s Charleston Harbor Post 45 project manager, Brian Williams,
yells back at one of his team members not to forget his life jacket and hard hat, wanting to make sure
his team is safely equipped to board the shrimp boat. That doesn’t sound right; what would the Post
45 team have to do with this picture?
The Post 45 team contracted Athena Technologies to help gather critical data on 150 sites in the Charleston Harbor by collecting wash probes in the entrance channel to find out where hard material exists on the harbor floor. Choppy seas, coupled with the rain and wind of early spring, made this activity very challenging 20 miles offshore in Athena’s pontoon boat. During the first three weeks of work, the Athena crew was only able to sink about half a dozen wash probes due to the rough conditions offshore.

These conditions were jeopardizing Athena’s ability to complete the work on schedule, putting the Post
45 schedule at risk of slipping.

Outfitting the Miss Georgia and another leased shrimp boat with pumps, hoses, computers and a
GPS was a brilliant solution developed by Athena. Not only would the shrimp boats be able to counter
the harsh elements, they would allow the crew to remain offshore overnight, saving valuable time coming and going out to sea each day.

The Post 45 study is on a very aggressive schedule with a target of September 2015 to have a complet
ed recommendation to Congress and a final environmental impact statement. This piece of the study
is needed to help the Corps’ engineers quantify the amount of consolidated material that may need
to be removed during the deepening. The process involves shooting concentrated jets of water through loose material on the harbor floor until it hits something hard, such as rock. This will help determine how difficult it would be to dredge this portion of the entrance channel.

“What we actually do is turn on the jet pump, run the pipe until it hits refusal, whatever the mate-
rial is, and then disconnect the pump,” said Adam Freeze, a geologist with Athena Technologies. “The
process takes about two minutes per wash probe and is relatively straightforward. The toughest part
of collecting this information is anchoring precisely at the right location because sea conditions were
constantly changing.”

The locations were based on information Coastal Carolina University researchers found last fall by us-
ing side scan sonar. The sonar sent out a signal that, with the help of a computer, created a pro
file of the bottom.

“Rock is more expensive to dredge than sand or silt, so we will use this information when we are putting
together our cost estimate, which ultimately helps us select a plan to recommend for construction,” said
Williams. “We want to make informed decisions but at the same time not collect so much information it
takes longer to complete the study and costs millions more.”

In late April, Athena finished collecting the 150 priority samples, as well as 54 secondary samples,
needed. Using GPS and computers, the exact depth of where Athena encountered the hard material is
recorded. The Post 45 team is now analyzing that information to refine specific locations for obtain-
ing and testing approximately 10 core samples this summer, where rock or other consolidated material
may exist.