Sittin' at the Bottom of the Bay

Scientists tackle a number of coastal challenges that stem from shifting sediment that fills transport channels in the Pamlico Sound, including managing dredged materials to make room for ferries, uncovering items of cultural importance, and preserving valuable sea grass.

WANCHESE — Sitting in traffic is never fun. 

But it’s not quite so bad when you’re in a traffic jam waiting to drive on board one of the North Carolina Ferry System ships. There’s a boat ride ahead; wind, waves, seagulls, a water view of the coast... How bad can that be?

And as you drive your car onto the ferry, and look at the cars in front and in back of you, it’s doesn’t take long to realize just how important North Carolina’s ferry system is to residents and visitors of the state’s barrier islands on the Outer Banks. The ferries provide transportation to the mainland, emergency evacuation and even a tourist attraction.

However, Mother Nature doesn’t always cooperate; and we’re not talking about the wind and waves above the water. Currents on the bottom, pushed by the wind and waves, fill in the channels with sediment. It’s called shoaling, which can ground a ferry and shut down the channel pretty quickly.

“The North Carolina Department of Transportation has to maintain all of the channels for the ferry system, and in many cases these channels fill in naturally with sediments,” explains Dr. Mike Piehler, Associate Professor in Coastal Ecology and Biogeochemistry at the University of North Carolina Coastal Studies Institute. “And so they have to dredge them out, and when they do that they have to remove the material, widen it and deepen it to a size that will accommodate their ferries.”

The ferries require channels roughly 80 feet wide and eight feet deep to travel safely along the Outer Banks. The natural depth of Pamlico Sound is only about four feet. That means there’s quite a bit of sediment to move. 

For the longest time, dredged material was considered waste material. In fact the term for it was dredge spoil. It was dumped pretty much anywhere. But at a time when storms are getting stronger and sea levels are rising, that material is now considered a valuable commodity. 

So the Department of Transportation is teaming up with the UNC Coastal Studies Institute to look at how dredge material can be an asset and not a spoil. To do that, researchers are looking at the route of the emergency ferry. It runs from Stumpy Point on the mainland, across Pamlico Sound to a dock near Rodanthe on Hatteras Island. It’s a shallow, complex ecosystem.

You don’t want to just dig and dump, you want to do it smart,” explains Dr. Reide Corbett, Program Head of Coastal Processes at the UNC Coastal Studies Institute. “And the best way is to protect the environment and provide something that is needed by the residents, the NCDOT and everyone else who works out there.”
 
Researchers mapped the bottom of Pamlico Sound, creating a profile of the channel’s location as well as the shoals across the channel. The makeup of the sediment is being studied, as are the currents and the waves in Pamlico Sound, along with the tides. It’s not enough to know what’s on the bottom, it is also important to know how the sediment gets moved around.

“We are taking a comprehensive look at how the ecosystem function may be affected by dredging activity, and then we are looking at how we can minimize the negative effect and maximize positive effect as we figure out clever things to do with dredge material,” explains Piehler.

The project is also looking at the history of the area.

“The proposal is to widen and deepen a channel and that means there’s the potential there for something to be buried because the historical picture is incomplete or imperfect,” says Dr. Nathan Richards, Program Head of Maritime Heritage at the UNC Coastal Studies Institute. “If there is something there we want to know about it, and there is also the chance for the disposition of the dredge material and we want to make sure when you are dumping it you’re not inadvertently obscuring something that could be of cultural importance.”

Then there’s the sea grass, which makes Pamlico Sound a complex ecosystem and rich habitat.

“Sea grass provides tons of ecosystem functions,” says Piehler, looking at aerials of Pamlico Sound and pointing out the thick sea grass, which is visible from above. “It provides for fish, stabilizes shoreline, helps water quality, and if you covered it up you would see a decline in ecosystem function in the area. So the idea is to be as thoughtful of where we put the material.”

Those options include building new islands to create areas for oyster reefs and marsh habitat, stabilizing eroding shorelines and creating new wetlands for natural storm protection.

It’s a complicated challenge, balancing the requirements to keep a coastal ecosystem healthy as well as protect the communities on the barrier islands. It also needs to be cost effective.

“There is new habitat that can be created and you can protect the shoreline through the use of this material,” says Corbett. “We want to figure how much material will be produced, how much energy in the system will move the material around, the distribution of SAV (submerged aquatic vegetation) and some of these plants, and where can this efficiently and effectively be used.”


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