Barrier Island Dynamics
Although this is the title of one of our units, it's also the first of a series of posts about the coastal ecosystems and hurricanes. As we are awaiting re-entry to our town, we will begin discussing natural disasters. Anyone who was affected by Hurricane Florence, we are with you.
If you were to take aerial photographs of the eastern coastline and Gulf coast of the United States, you would see that it is dotted with elongated islands of sand parallel to the main continent. These islands are collectively called barrier islands. They all have similar habitats consisting of dunes, maritime forests, marshes, and tidal flats. Over the years, these islands have also been heavily developed by humans, who have created popular shore towns and vacation areas.
On a typical barrier island, the beaches gently slope from the dunes down to the ocean. Depending on the location, the sand that creates these islands can be fine-grained or coarse-grained and tan to white in color. Scattered among the sand grains are rocks that have yet to be broken down by the ocean, shells from mollusks and crustaceans, and natural and man-made debris. On the opposite side of the dunes, vegetation grows in more abundance until they reach the lagoon. When the tide ebbs, mud flats are exposed, as are the species that live in and around the muddy bottom. Beyond the mud flats are the scattered salt marsh islands or marsh hammocks.
A natural barrier island ebbs and flows, just as tides will do daily. On one side of the island, waves, currents, tides, and winds will erode the sand away; on the other side, the sand will accrue. Barrier islands will change shape and appear to move closer to the mainland and north or south parallel to the coastline as time progresses. Because of this natural shift in the landscape, and the over-development of these islands, decision makers have added hardened structures to literally stop an island from moving altogether. These structures, such as rock sea walls, bulkheads, groins, and jetties, were once thought of as permanent solutions to the problem of barrier island movement and erosion. What decisions makers failed to realize was that these hardened structures not only continued to allow coastal erosion to occur, it exacerbated the problem.
When storm surges, hurricanes, and tropical storms come in contact with barrier islands, they are slowed down and their power is slightly diminished. The main purpose of a barrier island is to act as a “barrier” for the mainland. When coastal erosion, due to the placement of hardened structures (like roads and houses) occurs, these natural phenomena have no place to go but across the islands and directly onto the mainland. This is called overwash.
Because barrier islands were never created to withstand the urbanization they now have, overwash will occur during almost every powerful storm. With this overwash will come storm surges that can virtually wipe out whole neighborhoods. With global climate change, our "normal" hurricane season (typically June through November) has been producing stronger and more frequent storms. The result is catastrophic both financially to the tourist industry and to the homeowners.
As we piece our lives back together after a hurricane or other natural disaster, let's remember that the barrier island is nature's way of protecting the shoreline. Although we regularly visit or decide to live on these natural structures, they were created to withstand the power of the forces of nature. Unfortunately, our buildings and roads were not. As we alter these islands to suit our needs, nature will continue to do the same.