One of the most common forms of hard shoreline stabilization is the seawall. Seawalls, like most other long-term stabilization strategies, are generally made of concrete or rock, and are used because of their relatively low up-front cost. Seawalls are generally constructed along coasts to protect buildings and roads from beach erosion. Because we have built homes and businesses too close to the water, and as a result of rapidly rising sea levels and accelerating coastal erosion, seawalls are frequently built to provide fast and effective barriers from the tides. That said, they fail to defend beachfront properties from overwash, hurricanes, or storm-surge flooding, and they must be replaced with larger, more expensive seawalls over time.
Seawalls are a simple method of stabilization, as they are implemented to block the waves from reaching a certain point on the beach. While they are relatively effective in a short period of time, they are the most damaging form of shoreline stabilization in the long-run. More specifically, seawalls reflect breaking waves, which causes them to have higher energy as they recede. This, in turn, results in the waves removing more sand from the beach, and speeding up the process of erosion, as seen in the diagram below. Furthermore, the waves will eventually remove the sand from underneath the seawall, causing the structure itself to be destroyed after a total loss of the beach. Seawalls also worsen erosion because they cause the offshore profile of the beach to steepen, which results in higher-energy waves. The facts that the seawalls are built parallel to the shoreline also makes it impossible for dunes to transfer sand to the beach, which undermines yet another defense against the tides.
A valuable case study of the drawbacks of seawalls is North Topsail Beach, North Carolina. In 1999, following a storm surge caused by Hurricane Floyd, the owners of the Villa Capriani resort installed a 114-foot-long bulkhead consisting of interlocking vinyl sheets and sandbags going nine feet into the sand. A bulkhead differs from a seawall in that it is a softer/more temporary form of stabilization. They usually consist of reinforced sandbags or rock piles, and function like a seawall.
The North Topsail Beach bulkhead is reinforced with 16-foot-long pilings and should be in clear violation of North Carolina’s ban on seawall construction. While the bulkhead was created to protect the resort from a storm surge, the structure has been left in place since its creation. This is a strategy that is commonly used by North Carolina beachfront property owners, in which they install temporary stabilization structures under a permit, but they do not remove them. In doing so, they are able to legally erect “soft stabilization” structures that are, for all intents and purposes, forms of hard stabilization.
Unfortunately, the long-term use of this bulkhead has vastly eroded the beach along North Topsail, as seen in the photograph below. Now, the tides regularly reach the Villa Capriani resort and nearby beachfront houses, and the bulkhead has become the final line of defense protecting them from destruction. Had the buildings not been constructed so close to the ocean in the first place, or if the bulkhead was removed shortly after its construction, the issue would not have become so extreme.
Since the owners of the Villa Capriani resort were given a permit to construct the bulkhead, the responsibility fell on the N.C. Division of Coastal Management to file a lawsuit against Topsail Beach. More specifically, they demanded that the owners of the Villa Capriani resort remove the bulkhead, and even offered 6,800$ to assist in the removal. However, because the owners were given a permit, the lawsuit was not won, and the bulkhead remains in place today.
Works Referenced:
https://www.starnewsonline.com/article/NC/20010925/news/605098874/WM
https://www.newsobserver.com/news/local/article217026850.html