Introduction
In the South Pacific, Papua New Guinea’s Carteret islands are being drowned by rising sea levels. This didn't happen overnight but over the past 20 years, the inhabitants of these islands have watched their homes being washed away by waves and their fruit trees die as the water supply became increasingly saline, contaminated by rising sea levels. The islands were eventually drowned by the sea in the year 2000 and the inhabitants were relocated to the sister island.
This may answer the question as to why a study of Jamaica’s coastal erosion is imperative, what happened in Papua New Guinea could very much happen to us here in Jamaica if we fail to implement restorative and combative measures to curb the erosion of our beloved beaches. This report seeks to create awareness as to what causes coastal erosion and measures that can be implemented to preserve our coastline. In order to have a better understanding of how beaches are eroded we have included the formation of waves and the types of waves. There are a lot of illustrative photographs that will aid in better understanding the topic of coastal erosion.
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How oceanic waves are formed?
An ocean wave is a disturbance in the ocean that transmits energy from one place to another. Where does a wave's energy come from? There are a few types of ocean waves and they are generally classified by the energy source that creates them. The main types of ocean waves are those created by the wind (surface waves), created by adverse weather (storm surges), or those created by an earthquake (tsunamis).
(NOAA, 2018) stated that waves are created by energy passing through water, causing it to move in a circular motion. (NOAA, 2018) also mentioned that ocean waves transmit energy, and not water, across the ocean, and if not obstructed by anything, they have the potential to travel across an entire ocean basin.
According to (NOAA, 2018), waves are most commonly caused by wind. Wind-driven waves, or surface waves, are created by the friction between wind and surface water. (NOAA, 2018) also stated that as the wind blows across the surface of the ocean or a lake, the continual disturbance creates a wave crest. These types of waves are found globally across the open ocean and along the coast.
(Drughi, 2017) mentions that ocean waves are also formed by the gravitational pull between the earth, moon, and sun. (Drughi, 2017) noted that when waves are formed by the gravitational pull between the earth, moon, and the sun it creates tides, which are known as tidal waves.
Classification of Ocean Waves
Ocean waves may be classified into two major groups, constructive and destructive. Constructive waves possess a limited amount of energy with strong swash. They break on shore depositing materials thus increasing beach material and creating shallow and long beaches. These waves are lower in height and are less frequent – lasting for about 6-8 waves per minute.
Destructive waves on the other hand possess a greater amount of energy when compared to constructive waves. They have a strong backwash removing a portion of the coast or beach. As a result, these waves are usually steeper and shorter beaches. Destructive waves are higher and more frequent lasting for 12-14 waves per minute.
Ocean waves are further classified into several groups depending on the characteristics of size, period, and the way they are formed. The following are the major types of ocean waves:
- Capillary Waves
- Ultra Gravity and Ordinary Gravity Waves
- Chop waves
- Swells.
- Seiches
- Tsunamis
Effects of Waves on the Coast
Ocean waves distribute sand along the coast and onto beaches, where it is continuously recycled between surf zone bars, the beach, and dunes.
However, the destructive nature of waves is experienced during East Coast Low (ECL) storms, damaging coastal environments, properties, and infrastructure. During ECLs, sand is eroded from beaches and moved offshore into surf zone bars, which break wave’s father from the shore and ultimately limit destructive waves’ energy at the beach.
Waves are most commonly caused by wind. Wind-driven waves or surface waves are created by the friction between wind and surface water. As the wind blows across the surface of the ocean or a lake, the continual disturbance creates a wave crest. These types of waves are found globally across the open ocean and along the coast.
One of the most well-known waves affecting the coastline is the longshore or the littoral current. These are ocean currents that are created by waves that are refracted as they enter the shoreline. Longshore waves are generated within the surf zone when the front end of the wave is slowly pushing onto the shore, while the back of the wave moves faster traveling parallel to the coast as it remains in deeper water.
Coastal Erosion and Headlands
Coastal erosion which is the wearing away of coastal land or beaches is mainly caused by the impact of waves along the shoreline. This is accentuated during storms when waves are large and crash on shores with a lot of energy. (Dr. Rebecca Gllaspy Instructor)
If a coastal structure, such as a headland, which is a narrow strip of land that projects out into a body of water, contains cracks or crevices, waves can force water into the openings, breaking land and rock particles. Structures along the coast that are stony are also exposed to erosion caused by sand and rocks traveling within waves; as the sand and rocks pound against the coast, they grind away land and rocks. (Dr. Rebecca Gllaspy Instructor)
The Shoreline
Beaches and shorelines 30 years ago are now looking different. This is a result of coastal areas constantly changing form and shape due to the impact of waves. Waves continually erode the shoreline creating some unique features along the shore; a wave-cut cliff is a steep rock face formed by eroding actions of waves. The continuous hitting of supporting rocks by waves creates a notch and the rock which overhang the erosion weakens and crumbles, causing the cliff to retreat further inland. (Dr. Rebecca Gllaspy Instructor)
Wave Deposition
Waves carry many materials such as sand, shells, and small rocks. These materials are deposited on the shoreline forming beaches. A beach is any area of shoreline that is made of material deposited by waves.
Offshore deposits
Longshore currents can carry beach material offshore. The process of offshore deposits can produce landforms in open water, which may include sandbars and Barrier Island
Mitigation and Remedial Approaches to Coastal Erosion
There are many ways to mitigate the effects of waves which cause coastal erosion. In choosing a method to mitigate coastal erosion one has to take into account the size of the project, the cost, and the impact it will have on the immediate environment. There are natural measures such as planting vegetation and there are man-made measures, such as building seawalls and groins.
Vegetation
Vegetation is a natural way to remedy the effects of coastal erosion. The planting of vegetation helps to keep the sand anchored and thereby reduces the movement along the beach. Compared to manmade forms of mitigation, vegetation is natural, enhances the natural look of the surroundings, and is generally more cost-effective than manmade features. (Anon, 2007)
Seawall
The use of seawalls is one of the most intuitive methods for mitigating coastal erosion. These are massive structures built along the coastline to prevent waves from contacting the shore and hence stop their destructive properties. One of the disadvantages of seawalls is that it changes the natural look of the environment. (Florida, 2018)
Groin
A groin is a shore protection structure built perpendicular to the shoreline of the coast. The main purpose of the groin is to stop the long-shore drift and trap sediments. To do this a series of groins are built along the beach and these stop long-shore drift by blocking the movement of sand and keeping it in a specific area of the beach. This method can be cheaper than using a seawall, but it greatly distorts the look of the beach.
Other structures which can mitigate coastal erosion are:
- Breakwaters: Built offshore to break the energy of the waves before they reach the coastline
- Beach Nourishment: physically replenishing sand on a beach
- Jetties
- Revetments
Reference
- Anon, (2007). Mitigating Shore Erosion along Sheltered Coasts.
- Briney, A. (2018). All You Ever Needed to Know About Ocean Waves. Retrieved from https://www.thoughtco.com/what-are-waves-1435368
- Drughi, O. (2017). How Are Waves Formed? The Anatomy of a Perfect Wave. Retrieved from https://www.booksurfcamps.com/news/how-waves-are-formed
- Florida, F. (2018). Ways to Prevent Beach Erosion | Seawall Professionals of Florida. [Sea Wall Pros. Available at: http://www.seawallprosfl.com/ways-to-prevent-beach-erosion
- Gillaspy, R. (2018). The Effects of Coastal Erosion on Shoreline Features - Video & Lesson Transcript | Study.com. Retrieved from https://study.com/academy/lesson/the-effects-of-coastal-erosion-on-shoreline-features.html
- NOAA. (2018). Why does the ocean have waves? Referenced from: https://oceanservice.noaa.gov/facts/wavesinocean.html
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