For property owners directly on the shoreline, protection against erosion has become synonymous with protecting their property. There are several methods that are generally employed that involve structural construction on and near the shoreline. Two methods that are sometimes confused are the breakwater and seawall. However, they are quite different. Let's take a closer look at these two types of construction.
Related Blog: What is a Seawall and How Does it Work?
What Is a Breakwater?
Unlike a seawall which is built directly on the shoreline, a breakwater is built along the shoreline, and can extend seaward from the shore by some distance, or even not be attached to the shore at all as a detached breakwater. A breakwater is generally constructed out of rocks or concrete, creating a wall, or even a submerged barrier that runs parallel to the shore. This barrier breaks the wave prior to its reaching the shore, dissipating the energy with which it meets the shore. One common use of a breakwater is to create a small harbor where boats might be docked while being protected from open sea.
A submerged breakwater, one which is constructed to be below the ocean's surface, is generally placed for the purposes of reducing the effects of erosion. This is sometimes even called an artificial reef and has been used in the past especially to reduce the erosion of beaches. However, whether the purpose is to directly reduce erosion or to provide a protected area for boats, using a breakwater always creates additional erosion effects in the surrounding areas.
The breakwater breaks up the natural flow of sediment, both in its immediate area as well as along the surrounding shoreline. The breakwater itself tends to act as a sediment magnet, but can also cause the areas around it to be heavily depleted from sand and sediment. The installation of a breakwater requires careful monitoring of the sediment in the immediate and surrounding areas. Failure to do so can lead to erosion damages and losses that are a great deal more financially extensive than the original cost of constructing the breakwater.
What Is a Seawall?
A seawall is built directly on the shoreline. Seawalls are generally used to protect against erosion and are a common method to protect at-risk roadways and structures. They can help mitigate flooding problems. Additionally, they are a great preventative measure to stop problems from being created. A seawall can be built of a wide range of materials, including concrete, and can be finished in a wide variety of materials, including wood retention (primarily used for freshwater structures), composite, vinyl, and steel. Like a breakwater, a seawall also works by deflecting the waves which hit the shore. Because they do this directly from the shoreline, it is vital that they are well constructed to withstand the full force of the tides, and that the most appropriate material is selected for the location and intended primary purposes.
A seawall will influence surrounding erosion patterns. Beaches, directly where a seawall is built are sometimes lost. This effect is caused when the waves are so strongly deflected that they create a strong backwash which pulls the beach sand with it. This effect can be mitigated by creating a wall that has grooves in it to dissipate the force against the wall more effectively. The shoreline immediately surrounding a seawall, that is not itself protected from a seawall, is likely to face additional force from the surf. This leads to what is called flanking erosion when wave energy is redirected sideways, along the shoreline. However, this is nowhere near the extreme shifts that a breakwater has the potential to cause in the nearby shoreline.