Spencer Rogers, Extension Specialist
North Carolina Sea Grant College Program
Center for Marine Sciences
There are many solutions to the development problems evident on the coast. The question is which solution works the best for everyone?
An extreme view is that all barrier islands should be left undeveloped because they are so young and changeable. For example, the Pyramids should not be constructed on barrier islands because they are older than the islands.
Maximum wave height is controlled by water depth. Shallow water causes waves to break.
The shape of the shoreline (including dunes, beach, and nearshore environment is not accidental.
The shape is controlled by
Change any of the above and the shape of the beach is changed.
Storm waves tend to “flatten” the slope of the beach. The berm is erased and the dunes are eroded. Sand from these areas is moved into the nearshore area.
The offshore bar knocks down waves reducing their impact on the shore.
Typically, erosion of the dune and berm occurs quickly and then erosion eases during a storm.
More sand between your home and the water is better and safer. Low areas like walkways through the dunes are bad. They become washover conduits.
To construct dunes, you need:
Winds above 7 miles per hour move sand. Sand moves in zone from 0-6 inches above the surface of the ground. Nutrients are brought in with this sand and nourish the vegetation.
Dune growth is typically asymmetrical with the more rapid growth on the seaward side.
How do we avoid storm damage?
The rate of change is so great along the shoreline that you should not rebuild in the same spot after partial or total destruction of a structure.
Erosion in NC is 2-3 feet per year on the average.
Inlets are chronic erosion problem areas. Oregon Inlet is an example. Many homes have been lost as Oregon Inlet has migrated to the south since 1848. The shoreline in the vicinity of inlets is driven landward.
The worst erosion in NC is along inlet shorelines.
How do we reduce risk to life and property in the coastal area?
Know the historic erosion rate for an area and build accordingly.
Move buildings that become threatened
Like Paul Foster's house on Figure Eight Island, it is cheapest to move to back of existing lot.
more expensive if one has to buy another lot
Setting houses back as far as possible on lot at the start would reduce problems with eroding shoreline.
Seawalls
Granted that seawalls cause scour on shoreline.
Seawalls are designed to prevent shoreline from encroaching on a structure. From that point of view, they are successful.
The Galveston Seawall, built after a devastating hurricane in 1900, was designed to prevent the ocean from overtopping the town. From that point of view, it has been highly successful. If you want a beach, well, that is another problem.
In North Carolina, a seawall was constructed to save Fort Fisher. The earthen fort could not be moved so the shoreline had to be hardened. The fort is now protected. There is no beach there now.
Other measures to respond to shoreline erosion: