Types Of Shoreline Protection
Historically, the structures developed for shoreline protection were constructed of durable materials such as rock and reinforced concrete. They were designed to withstand the force of wave action. Such "hard" stabilization methods are still in use today and include seawalls, revetments, breakwaters, impermeable groins, and jetties.
Seawalls are structures built at the water's edge of concrete or large stone (riprap). Their purpose is to bear the full brunt of the wave action, thereby protecting the cliff face. However, they also encourage the beach in front of them to narrow. In addition, they are considered an eyesore to many people.
Revetments of broken concrete or riprap are powerful devices for reducing the energy from wave action, and they are repaired inexpensively. Their irregular surface offers protection from wave runup, or the movement of breaking waves up the shore. Revetments often limit access to the beach and, as with seawalls, they can be rather unsightly.
Groins are sediment traps. They jut out at right angles from the shore and catch sediment carried by long-shore drift on their upcurrent side. However, this sediment never reaches the downcurrent side of the groin, so the beach narrows. For this reason multiple groins are usually constructed in an area.
Breakwaters may be connected to the shoreline at one end or completely separate from it. Their purpose is to bear the brunt of the waves, producing calmer water shoreward of the structure. Jetties are used to keep a channel open and are placed one on each side of the channel's outlet. Both of these structures impact littoral longshore transport causing beach buildup on their up-drift sides and erosion downdrift. Dredging is often required to keep them functioning.
While "hard" structures continue to be used for shoreline defense, "soft" stabilization methods are becoming more prevalent in coastal areas, either as the sole method of protection or in conjunction with "hard" stabilization practices. The most utilized form of "soft" shoreline protection is beach nourishment, or the replenishing of sands on an eroding or retreating beach. Its greatest advantage is that nourishment extends the time until erosion undermines the structures behind the beach. Beach nourishment also allows for a wider, more usable beach, which provides better recreational areas and economic revenue for those living near it. But it also has disadvantages. It is extremely costly, and nourishment must be performed every few years to keep beaches from retreating after storms. In addition, impacts to the beach ecosystem often occur during, or as a result of, the nourishment. If excessively muddy sands are used, organisms may be smothered, and building beaches steeper than their original profile may limit their use by various forms of marine life.
Recently new types of "soft" stabilization have been introduced. Wave screens, submerged breakwaters, active submerged breakwaters and floating breakwaters do not disturb or change current flow, but rather allow water and fish to pass through their partially transparent structure. Improved physical structures that aid in shoreline protection are not the only ideas under consideration for the future. Enhancement of the environment through vegetation of the shores and an understanding of how each inhabitant of the shore environment contributes to the health and well being of the coast must play an active part in coastal planning.
For example, recent research has shown the eggs of the Loggerhead turtle provide much-needed nutrients to beach areas where they nest. These nutrients ensure healthy stands of coastal vegetation, which help keep the beach in place. In an effort to protect the threatened turtles, their nests are often relocated, depriving the original nesting sites of these nutrients. Taking into account such nuances when considering the type of shoreline protection to use will allow for a more complete and natural form of shoreline protection.
Past trends in shoreline protection have involved fighting the sea with expensive engineered defenses. The realization that shorelines are dynamic and erosion is a natural and inevitable process has more recently led to some revolutionary and certainly controversial ideas in the fight against shoreline erosion. Sea levels are expected to continue their current rate of rise or to accelerate. Should they increase dramatically, expensive engineered structures and replenished beaches will be no match for the sea. Some communities have considered the idea of relocating buildings. Along very densely populated coastlines this is not really a feasible alternative, but the idea of restricting coastal development is gaining supporters. North Carolina has strict regulations governing the types and sizes of structures that can be built on its shoreline. Many believe we must establish wise shoreline land use and development guidelines, and that if we choose to build near the shore it is only with the understanding that structures constructed there are not considered permanent and will be given up to the sea should shorelines move landward.
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