Scientists Examine Geologic Processes in Chincoteague Inlet Study

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VIMS photo.

By Carol Vaughn —

Chris Hein, of the Virginia Institute of Marine Science, updated the Chincoteague Town Council on a study of the Chincoteague Inlet.
The study, called the Chincoteague Inlet Modeling Study (CIMS), has been going on around 2 1/2 years and is entering a new phase, according to Hein.
“We want to get some perspective. We want to understand Chincoteague. We want to understand the likelihood of the breech happening (on southern Assateague). We want to understand the likelihood of Wallops growing wider if Assateague continues to move to the south,” he said.
The project’s first stage was mapping the geological history of Assateague and Chincoteague to better predict the future. Researchers collected sediment cores anywhere from 30 feet below the surface to around 90 feet down, according to Hein.
“We have to understand the rates at which that has happened — how it has happened in the past. And for that, we rely on the geological record,” Hein said, noting ridges on Chincoteague mark old shorelines.
Additionally, scientists used ground-penetrating radar as well as using a geochemical tool to date beach areas and determine when they formed.
They found Piney Island dates to around A.D. 1600; the middle of Chincoteague dates to around A.D. 730; and the oldest part of Chincoteague, to the west, dates to 250 B.C.
“This started as a series of barrier islands, just like Cedar Island, just like Wallops Island, migrating landward,” Hein said, adding, “… And then, in time, it starts to grow. It stops moving, stabilizes.”
By 1880, maps show Chincoteague was fully fronted by Assateague to the east. Assateague’s southern end has continued to grow after that.
Hein noted Chincoteague has benefited from having Assateague to its east, protecting Chincoteague from the ocean.
Still, the marshy shoreline on Chincoteague’s southern end is eroding — in part, that is the impetus for the study.
Other barrier islands off the Eastern Shore, without protection from the sea, are moving rapidly landward — in some cases, such as Parramore Island and Hog Island, “those are largely just eroding…and losing area,” Hein said. Some are moving up to 30 or 40 feet per year.
“This is a very strange part of the Virginia barrier island system,” Hein said, noting outside of Fishermans Island, which also has grown, northern Wallops Island and southern Assateague are “the only parts of this entire system that have been growing through time.”
He showed the council diagrams showing changes over time.
“One of the motivating questions, one of the things you have to ask yourself when you look at a diagram like that is, if Assateague has grown up in this way,” and the hook at Tom’s Cove is just about 100 years old, “what’s going to happen in the next 100 years?” Hein said.
There are two likely possibilities, he said.
“One, what’s happened in the past continues to happen in the future,” meaning Assateague’s southern end continues to grow, eventually, in 100 years or so, extending in front of Wallops Island.
In that scenario, Chincoteague Inlet would move, making boats’ trip from Chincoteague to the ocean longer, but also meaning Chincoteague and Wallops would be protected.
A second possibility is that a new inlet forms in the Tom’s Cove area, creating a new island south of it.
“It’s possible it’s happened before,” Hein said, noting geological evidence.
That inlet also could later close, “but it might not,” he said.
Hein noted Winter Storm Jonas, in 2016, resulted in breeches on Assateague, which later closed.
Hein also spoke about nearer-term concerns — “the threats today” — which include the continued widening of Chincoteague Inlet.
“We’re all well aware of the problems that have occurred there,” he said, adding, “… But, that reorientation has changed what we call the exposure.”
Waves coming from the south, which is what happens most of the time, are large enough to cause erosion and sand that used to make it all the way around to the inlet is getting stuck at Assateague.
About whether it would ever make sense to consider moving sand artificially, Hein said, “We’re talking money here, of course — but it is one thing to think about. if it looked like that before, it could again. It’s not that something has changed in the system. It’s just that we don’t have a way to keep it closed.”
“What’s going on over at Wallops is another challenge … to Chincoteague and its inlet,” Hein said.
Breakwaters at Wallops and dredging “is altering the shape of the beach, which alters the shape of the inlet, which alters the wave energy,” Hein said.
Still, dredging off Wallops also presents opportunities to potentially use spoils to build up land, he noted.
One of the things researchers want to do with the model is explore what could happen if an inlet forms on southern Assateague.
“How stable is that? What does it mean for wave energy reaching Chincoteague Island? What does it mean for currents going through here?” Hein said.
They also want to look at the other possibility — that Assateague’s southern end continues to grow.
In order to test these longer-term questions, “as well as to test these really management-scale questions,” including what to do about erosion of southern Chincoteague, researchers will rely on the CIMS model.
The model is a hydrodynamic sediment transport model — it simulates how waves, currents, and tides move and how they move sediment.
To develop the model, scientists first worked to create a grid of water depths, using NOAA data for Chincoteague Inlet collected in 2015 and data VIMS and University of Delaware scientists collected more recently.
Scientists also have been collecting data about tides, currents, waves, and sediment types.
With the model completed, scientists can try out scenarios, including looking at potential effects of different human actions, such as hardening the shoreline of southern Chincoteague.
“We’re going to answer the question, what kind of wave energy is possible there. Therefore, what size of a structure do we need to build? What would actually work to protect it?” Hein said.
“We have the model working. Now we are tweaking elevations in the grid,” he said.
This fall, scientists will be using the model to explore different management strategies, such as putting breakwaters off southern Chincoteague, beneficial use of dredge spoils, and others.
“It’s a model. It’s an experiment. It’s a way to test things. It’s not a life-or-death kind of answer, although I know that some of the implications are massive around here,” Hein said.