By JOY CRIST
Earlier in 2017, the National Park Service created a series of maps to determine how erosion has affected regions of Hatteras Island in the past 150 years or so.
Per David Hallac, Cape Hatteras National Seashore Superintendent, the creation of the maps stemmed from a conversation with local property owners in Avon, after an especially brutal winter, erosion-wise.
Lifelong locals will attest that the island shifts and moves on a regular basis. A beach that was nice and wide in the summer months can narrow to just a sliver in the winter, and then return to its wide summertime status once again the following year.
But examining the timeline of where the shoreline was 150, 50, or even just 10 years ago really puts the longer-term changes in perspective.
This is one of those cases where a picture really is worth a thousand words. You can see the map of the long-term changes in the Avon and Buxton shorelines by clicking here.
?We should have known how much the beach has changed,? said David Hallac. ?But having us plot the data for ourselves, when it really sunk in, it was very surprising.?
Let?s start by taking a closer look at the map. The individual lines represent where the shoreline was at a given time period, beginning with the 1852 survey and continuing all the way to 2016 / 2017.
There are two areas in particular that immediately jump out to casual viewers.
The first region is the area in between Buxton and Avon ? an area that is currently undergoing an extensive summer-long beach nourishment project. In 1852, this area was roughly three times as wide as it is now, with most of the former land mass and shoreline disappearing before 1980.
The other Area is southern Avon, which is examined in closer detail in the call-out box.
Unlike the region in between Avon and Buxton, which drastically changed in the late 1800s and early 1900s, this section of the island has undergone the most change in the past 20-40 years. Just look at where the shoreline was in 1980, 1997, and 2016. As Hallac pointed out, in just the past 20 years, an area the size of two rows of homes has effectively disappeared.
Several of these areas that are most effected by erosion ? which are scattered throughout the Outer Banks ? also have another unique feature that wasn?t in place 20, 30, or 100 years ago ? namely, narrow and steep beaches.
So why is this happening, and what has changed the barrier island landscape?
East Carolina University geologist Dr. Stan Riggs, who has been doing research on modern coastal systems since 1964, explains the situation.
?The whole shore-face is now locked in place because of construction of Highway 12 [and structures],? says Dr. Riggs. ?The beach can no longer migrate upward and landward in response to ongoing rise in sea level. Consequently, the beach gets steeper and steeper, with less powerful storms making bigger impacts and changes.?
Essentially, it all boils down to the frequency, type, and magnitude of storms that produce the storm surges and wave energy.
Optimally, when a nor?easter, hurricane, or big swell hits the barrier islands, the storm surge and associated waves flood over the shoreline, eroding the beach sand and redepositing it on top of the island to build elevation. The uninhabited Core Banks just south of the Outer Banks is a good example of this natural process.
?The Core Banks has doubled its vertical elevation since the 1960s? says Dr. Riggs. ?Today, they are generally high and wide with heavy vegetative cover?they are probably the healthiest barrier islands in the country.?
But when you have fixed homes, buildings, and roads to maintain, it?s impossible to let the ocean or sound dictate where storm sand and water should go.
As such, the creation of dune dikes and other protective measures are taken, and instead of pushing sand and water to other parts of the island, the ocean / sound erodes the barrier beaches, removing sand and creating steep scarps in the dune dikes.
?Those dune dikes stop the overwash. Storm surge would normally go over the top, and deposit 1-2 meters of new sand on top of and behind the barriers. So by stopping the overwash, the beach gets steeper [and] narrower,? says Dr. Riggs.
?Skinny little barrier islands have always been overwashed. This is something the locals knew from day one,? adds Dr. Riggs, noting that a century ago, the barrier island communities were located closer to the sound than the ocean.
?We?ve lost more than 50% of the width of the island since 1852. And as long as we maintain human structures on the island, the islands can?t rebuild and keep up with rising sea level.?
This may sound bleak on the surface, but it?s essential to remember how much a storm ? or lack of storms ? can also change the landscape.
?The rate of shoreline erosion is seasonal, and it?s a function of the storm patterns,? said Dr. Riggs. ?There was a period of time from about the mid-1960s until the 1980s when we had very few storms. When that happens, not only does the erosion slow down, but in some cases the barrier islands actually grow seaward.?
And not all of the barrier islands are effected negatively by natural dynamics ? just examine Buxton Woods and the Shelly Island sandbar.
?Look at an aerial photograph of Buxton Woods,? says Dr. Riggs. ?The entire woods is made of a series of accretionary beach ridges that grew seaward and are still growing.?
?This area has a major source of new sand, which is Diamond Shoals,? he adds. ?Storms in the Diamond Shoals area can move new sand from the shoals and build new beach ridges that weld onto the south shore of Buxton Woods.?
?The new Shelley Island is probably the next ridge that?s going to weld onto the Buxton Woods shoreline. We dated the landward-most ridge on the Pamlico Sound side of Buxton Woods and it formed about 1700 years ago. While most beaches are eroding and the shorelines receding, Buxton Woods is growing. And this new island is probably the next part.?
The weather patterns over the last few months formed Shelly Island, as well dictated the shape of Cape Point.
?Right now, Cape Point is really long,? says Dr. Riggs. ?That?s because of local weather conditions that have been taking place since last November.?
Simply put, the future of the island landscape can change dramatically, and nothing is set in stone (or sand.) A few months of no nor?easters or an extended period of gentle weather can create entire new beach dynamics, as Shelly Island sandbar certainly proves.
Just think of our local landscape this summer which has brought wide beaches and tons of visitors to enjoy them ? just like other summers. But could this current landscape change? Yes, and based on the shifting shoreline over the past 150 years or so, it likely will.
There?s not an easy solution to the erosion problem, no question about it. There?s been talk about addressing certain hot spots throughout the barrier island system in the not-so-distant future, but the cost of replenishing 70 miles of beaches is difficult at best, and it is hard to know which regions will be most problematic in the next few years.
It will require a delicate balance to keep both our beaches and our highway. And it?s a question that will continually garner attention in the years to come.
But understanding the history of the island?s geology, as well as the dynamics that continue to shape and change the mobile barrier islands, is a solid first step to understanding the issues, according to Dr. Riggs.
?It pays to understand how these narrow piles of sand are working, that?s for sure.?
