24/7 dredging operation taxes machines, ensures
sea turtles return home
Those in the industry know all too well that dredging is no business for the weak-of-heart or the ill-equipped, and a project ongoing in Pawleys Island, South Carolina is no exception. After over ten years of struggling to receive the green light from government and environmental organizations to deepen the waterways that separate the island from the mainland, the town finally launched the project last November. It will relocate 38,000 cubic yards of sediment from the beds of two salt marsh creeks that separate the resort island town from the mainland, to the two major recreational beaches at either end of the island.
And they'll do it all before the sea turtle population returns this spring to nest their eggs.
The creek beds, which have never been dredged, were reaching critical heights that would soon impact the sensitive estuary habitat and infringe on residents' ability to use the creeks for recreational uses like paddling, fishing and crabbing, according to town mayor, Bill Otis. He feels the creeks and the wildlife habitat they provide form a big part of Pawleys Island's personality and as such, fought hard to get this project under way despite some tough timelines. "This whole project is quite an achievement, really," said Otis. "It's a significant operation and it all has to take place, start to finish, during the sea turtle's off season."
Sea turtles come to the marsh in the spring to lay their eggs and stay through the summer, heading back to sea with their offspring the following fall, giving the town less than six months to complete the job.
These stringent time constraints have meant that the dredging firm contracted to carry out the project, EnviroDredge of Wilmington, North Carolina, has been working around the clock since they started in November 2007 to get the job done.
"We have two crews of five people working alternate 12-hour shifts seven days a week, and it's been like this since the project began," explained Jack Sharp, the construction manager for EnviroDredge. This kind of 24-hour operation taxes not only the human resources, but the equipment as well, and when you throw in the unexpected, the stresses only increase, he added.
In this case the unexpected has included challenges like the discovery that the sediment in the creek beds is riddled with large debris left behind by the numerous severe storms that hit this area on a regular basis, like 1989's hurricane Hugo. As well they discovered an abundance of shells that are not ideal for beach sand. When they started the hydraulic dredging project EnviroDredge was using an 8-foot wide auger cutting head on a dredge manufactured by Montana-based SRS Crisafulli and a six-inch sludge pump. Due to the density of the in-situ material this combination proved ineffective. "As soon as we discovered the large debris and shell content we knew there was no way the first machine was going to be able to do the job," said Sharp.
They quickly switched to a new cutter-suction dredge -- the Ellicott 8-inch Swinging Dragon -- which is capable of more aggressive digging and higher pumping volumes. It is equipped with a swinging ladder and a serrated tooth cutter head and can provide downward digging pressure with a hydraulic cylinder. Unlike its predecessor, the serrated cutter head is capable of agitating the virgin soil, comprised of sand, shell, mud, and stone as well as large debris, on the bottom of the waterway and the pump, a larger Metso-Mineral 8-inch pump, sucks the dirt up as it mixes with water. The process is aided by the addition of a booster pump to help transport the sand through the pipeline. This slurry is transported through an HDPE pipeline to a dewatering area -- in this case one of two beaches -- where the water and solid are separated as the sand falls out of suspension and the water goes into the ocean.
The initial dredge wasn't the only machine to feel the effects of the 24/7 job. In fact, only two of the ten of machines used on the project have not required repairs or replacing to this point. One of those two machines is the high performance Connectra 314 fusion machine.
Alan Berry is not surprised. His firm, Georgia Underground, provided the pipe, the fusion machine and the training required to operate it, for the project. "We have had to fuse together over twelve thousand feet of pipe on this project," said Berry, "and that (Connectra fusion) machine has not let us down, not once. Which is very welcome, I have to tell you, on a project like this." Berry credits the machine's simple, reliable design with its ability to endure the demanding, harsh work of dredging.
The crew is using HDPE SDR17 pipe, varying in diameter from 8-inches to 12-inches, fusing them with the Connectra 314 to create 500-foot lengths that are then flanged to create the 4,500- and 8,000-foot lengths required to reach the beaches at the north and south ends of the creeks, respectively.
At the beach sites large football field-sized basins have been dug to serve as dewatering areas where the water-logged sand drains. The sand will later be spread on the beach, replacing sand that has been eroded by the same storms that built up the sediment in the creek beds.
As this story goes to press, the $430,000 project is in its final weeks, projected to be completed by the end of March, and the mayor couldn't be happier. The town has successfully protected a precious resource for the wildlife and residents of Pawleys Island, he said, adding, "It's kind of like the birthing process after a long and difficult pregnancy -- we're just excited to see it done."
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