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Posted 6/3/2013

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By David Warren and Brian Williams
Project Management

When you ride over the Don N. Holt Bridge, the stretch of Interstate 526 connecting Charleston and North Charleston across the Cooper River, you probably see one of two things: a drought stricken lake with a crazy quilt of a gray-brown cracked surface or a lake that is brimming to the top. You probably also see backhoes digging and trucks driving around in circles on top of the dikes. And you probably think "what is going on down there?"

What you see down below are known as the life cycle phases of the Clouter Creek Disposal Area that is managed by the U.S. Army Corps of Engineers, Charleston District. The life cycle begins with dredging, which is when mud and sand, also known as dredge material, is sucked from the bottom of the Cooper River and transported through a pipe and pumped into the disposal cells. During this process it looks like a lake. Over time, the mud and sand drop out of the water and the water is released at a controlled rate back into the Cooper River. Next is the drying phase, which takes about 8-12 months for the water to drain and where you see the cracked surface that has the consistency of jelly.

The Corps can begin using long reach backhoes to dig a series of ditches to drain the trapped water into the mud mixture, better known as the ditching phase. The long reach backhoe is supported on a wooden mat as it works its way down the shaky surface carving out the ditch, used during the appropriately named ditching phase. As the backhoe is working it is literally floating on the mud mixture. This is the part of the business that is called the "art of working the mud." It takes a keen eye and years of experience to know when the mud is just right to support the equipment.

Finally, the last phase is diking; after several cycles of ditching the mud, the mixture is dry enough to dig out and use to make the dikes higher, which allows for more mud mixture to be put back into the cell. The trucks running around are spreading the dried mud mixture on top of the dikes to make them higher. This is a business that loves dry weather and fears hurricanes. With that, the cycle starts over again, dredging, drying, ditching and diking. The cycle allows each cell to recover and not be used constantly, extending the life of the cell.

"If we did not have these areas, we could not maintain and keep Charleston Harbor the economic engine that it is for the region," said Lt. Col. Ed Chamberlayne, the district commander with the U.S. Army Corps of Engineers.

As part of the ongoing Charleston Harbor Post 45 Feasibility Study, the District is evaluating the type and amount of dredge material that could be excavated from the Cooper River during any eventual deepening and widening of the upper reaches of the harbor. In addition, data has been collected and is being analyzed that will help determine the extent to which the elevation of the dikes can be increased in the future. This information will help the District plan for the future management of the disposal area as it continues to receive annual maintenance dredge material and could receive significant quantities of deepening material.

The disposal area was constructed in the mid 1980’s and is used on a rotating basis to receive the dredge material. The fours cells are named North, Highway, Middle and South. The navigation branch has a plan through the year 2020 to manage the capacity of each cell based on the previous amount of material that is placed into each cell every year.

In 2013 alone, the disposal area has received 1.38 million cubic yards of material from the Cooper River. North Cell is currently undergoing an extensive ditching project to prepare the material in the cell for dike raising. Middle Cell is in the preliminary drying phase with ditching scheduled for fiscal year 2014 to precede dike raising. Highway and South Cells are receiving material and have a combined capacity of 6.8 million cubic yards available, enough for five years of maintenance dredging at anticipated rates. The current plan is to design the North Cell dike raising project in 2014 with the actual construction due to take place in 2015.

So when you ride over the Clouter Creek Disposal Area and look down, you are seeing the ultimate play ground for adult kids; mud, sand, big trucks, backhoes and workers going to work every day by boat. Another day in paradise? Not when you step outside and the mosquitoes find you.

charleston harbor civil works construction post 45