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    Outer Banks Beach Nourishment

    January 24, 2017

    For more information on 2017 beach nourishment areas and timelines, visit our Beach Nourishment Info Page.

    On a beautiful summer’s day on the Outer Banks it’s hard to imagine the forces at work that shape the coastal shoreline. Waves seem like gentle riffles, larger perhaps than a wave on a lake or bay, but nothing like the legendary power of a nor’easter or tropical storm.

    The evidence, though, of the power of the sea is everywhere. In Kitty Hawk what is left of the dune line has been cutaway to a steeply sloping scarp just yards away from the road. In Duck homes have had to be moved back 50’ and 60’ as the ocean steadily encroaches.

    The process is not constant across the entire Outer Banks; in some areas there is an accretion or addition of sand to the beach. In other areas, the beach sometimes retreats, and sometimes grows. But in those areas where the loss of beach is greatest, there is often a concern about damage to roads, infrastructure, and property. As we know, the beaches are so important to the economy of the Outer Banks. There have been a number of approaches to protect property and infrastructure over the years; none as effective as beach nourishment.

    Beach Nourishment—What is happening on the Beach

    As wave energy moves toward the shore, the water depth become more shallow, and the energy at the bottom of the sea slows down as it comes in contact with the floor of the ocean. However, the top of the wave energy does not slow down, and when the difference between the bottom and top become great enough a wave is created.

    If this process did not happen, storm waves that have been measured at 30’-40’ would quickly overwhelm the Outer Banks, or any barrier island.Dredge Oregon Inlet

    Even after a wave breaks in the surf zone, there is still a tremendous amount of energy in it, and that is where the beach comes into play. From the tide mark—high or low tide in this case—to the dune line, the beach acts like a sponge absorbing the energy that is contained in every wave.

    There are a number of factors that determine why some areas of the shoreline lose more beach than others.

    Ocean storms play a significant role in shaping our shoreline, but just as importantly—perhaps even more significantly—is the geology of the ocean floor offshore.

    Offshore shoals can focus wave energy causing rapid loss of beach. That is what has happened at the S Curves just north of Rodanthe, where Wimble Shoals comes into play. It should also be noted that Wimble Shoals is also the reason why the surfing is so good at that particular beach.

    North of Oregon Inlet, the dominant marine geological feature is the ancient river channels from what was once the Roanoke River Delta. The rapid loss of beach north of the Black Pelican in Kitty Hawk is an excellent example of the effects of this ancient river bed.

    Beach Nourishment-How it works

    Beach nourishment works with the forces of nature to protect the shoreline. At first glance, especially during a nourishment process, it looks as though sand is simply being pumped on to the beach. It is far more complex than that.

    Oregon Inlet Beach NourishmentIt is very important that the grain size of the sand that is nourishing the beach matches the sand that is already there. If the grain size is too big, it will roll off the beach and into the ocean with a minimal effect. If it is too small, the sand will sift to the bottom of the beach, again with little or no effect.

    Sand for nourishment projects is almost always mined offshore. When an offshore source is found, if it is close enough, sand is pumped from the source to the beach. If it is farther offshore, it is dredged, loaded into hoppers and manually placed on the beach.

    When coastal geologists analyze a beach, they include the underwater area immediately adjacent to the visible beach. Beach nourishment projects expect some sand to move from the visible beach to the underwater area. There are two reasons why that is important. The accretion of sand on the bottom of the seabed helps to dissipate the force of the waves as they come ashore, and with sand in the ocean immediately offshore, it remains in the system and is a natural source of sand to replenish the beach.

    Nags Head Beach NourishmentSometimes the sand from the beach does move to deeper water, typically just past the shallow underwater beach. As the sand accretes in that deeper water zone, it will often form a sandbar, increasing the shoreline protection.

    Sand dunes are often, but not always, included in beach nourishment projects. Generally the last line of protection from the sea, the wider the beach, the more effective the dunes will be. The object is to allow the beach to absorb or dissipate as much of the wave energy as possible before the ocean reaches the dunes.

    For more information on 2017 beach nourishment areas and timelines, visit our Beach Nourishment Info Page.