Coastal Transportation

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Coastal transport

Coastal transport is an important coastal process that involves the movement of materials along the coast by the action of waves and winds. With the constant movement of waves, different materials are picked up and are transported to different areas, and can travel as far as thousands of kilometers. This coastal process helps maintain balance in marine environments as this continuously changes our ocean’s layout.

Various external factors greatly influence coastal transportation such as weather patterns, climate, and other hydrometeorological events. For example, as weather patterns become more intense, materials and sediments can be transported to farther distances. In general, aggressive weather events play an important role in the intensity of the ocean’s transportation activities.

Coastal landscapes continuously change because of these transportation events. For one, transportation can lead to the deposition and build-up of different sediments along coastlines, thus forming different depositional landforms. In other instances, transportation usually follows after the erosion and removal of materials along coastlines. For us to gain a better understanding of the other coastal processes, we must first look into what coastal transportation is.

What is Coastal Transportation?

Coastal transportation is the movement of different sediments and materials through the interaction between land and sea. Waves are the main drivers of coastal transportation, however different hydrometeorological events such as storms and typhoons also impact this coastal process. As wind blows and forms waves, the friction between the water and the sediments allows for the movement of these materials across oceans. These natural interactions subsequently continue to change our coastal landscapes. However, coastal transportation works not only on its own, but in tandem with other coastal processes such as deposition, erosion, and weathering.

Coastal zones experience the interaction of different energies and forces that greatly influence how sediments are moved. Gravity and friction, in particular, are some of the main forces that drive transportation activities. Because of the large amounts of force these exert, sediments and other particles are able to travel over significant distances.

Competence and capacity are two important terms used to describe coastal processes and the sediments they carry. Competence refers to the biggest size of material that an agent can transport. On the other hand, capacity refers to the maximum load an agent can transport. Both concepts help us describe the type and amount of sediments that can get transported by this coastal process.

In coastal areas, the swash, or forward movement of waves, and the backwash, or the backward movement of waves significantly contribute to the transportation of sediments along coastlines. The longshore drift, in particular, is the process of moving sediments along the coastline through waves that hit the shore obliquely. This process combines the swash and backwash of waves that form a zig-zag movement across shores, which is mainly due to the direction of the prevailing wind.

The ocean consists of different layers where sediments are suspended or are settled. At the seafloor, there is a significantly concentrated layer of sediments that are very sensitive to the movement of waters. As waves begin to form, some of these sediments get suspended and carried away to other areas of the sea. Furthermore, the seafloor’s thickness plays an important role in determining the impacts of the movement of water.

A suspension layer normally occurs over an extensive area on top of the saltation level. This layer usually contains a high concentration of sediment molecules that stay here for a long time. These sediments normally only move during a return current. Not all sediments however remain suspended, depending on their size and physical characteristics, some sediments float above the water’s surface or simply settle down at the seafloor. Depending on the energy exerted on them, different sediments will eventually get picked up and transported.

As mentioned, coastal transportation is not an independent process. Usually, after transporting materials to coastlines, wave energy is lost and thus, some sediments are deposited and begin to build-up in a process called coastal deposition. Furthermore, after coastal erosion events, the removed sediments and materials are then transported to different locations. The different types of waves that carry these sediments also help determine how far up the coastlines these sediments will travel to.

Many types of coastal transport allow for the coastal processes to happen, and many different physical changes occur to these sediments for the different types of coastal transport to occur. Aside from the longshore drift, let us look at the other types of coastal transportation.   

Types of Coastal Transportation 

As mentioned, coastal transportation happens because of the movement of material on the seabed. The various waves cause the creation of longshore drift, but a lot of elements help contribute to the transportation of these sediments during a longshore drift. The different elements and physical changes that form part of the longshore drift include the following: 

Solution

Solutions happen when minerals get dissolved in seawater and are carried in a solution. Usually the load here is not visible, since the sediments become incorporated with the seawater. Salt, for example, is a material that gets dissolved in the water, which gives rise to the ocean’s high salinity.

Saltation

Saltation is the process wherein materials bounce along the sea bed. This usually occurs for small pebbles and large sands grains that currents cannot keep afloat for long periods of time.

Suspension

Suspension occurs when sediments remain suspended in the water. These sediments are not too heavy that they settle down at the ocean floor, and are not too light that they remain afloat. Because these sediments remain suspended, they flow along with the waves, resulting in their transportation.

Traction

Traction occurs for heavy sediments that settle down at the ocean floor. Because of their weight, these sediments usually just roll at the bottom of the ocean floor. However, this type of coastal transportation is usually slow given the size of the sediments that are transported.

Frequently Asked Questions 

Why do we need coastal transportation? 

To allow for build-up processes to continue, the ocean constantly needs to move material around. Some transportation events result in the break-down of the coastal zones, and removed material gets transported to different areas. The movement of sediments, rocks, and materials plays a key role in our coastal processes. 

What are the key elements in the coastal transportation process?  

The key elements include the energy from waves, wind, and the sizes and physical characteristics of different sediments and materials to be transported

What types of material normally become transported by the sea?  

The materials transported by the sea include large boulders or rocks, refined material for example clay or sand, small particles and pebbles. Depending on their size, these sediments can get transported through different means.

Where does the sea transport the material to?  

Depending on the type of material transported and availability of spaces in coastal zones, waves can either transport these materials to beach areas of the bottom of the ocean.

What happens to material collected by the waves?  

Materials collected by the waves become transported and deposited in other spaces. These spaces include the beach areas or other places at the ocean bottoms or layer spaces. The build-up and deposition of these sediments results in the formation of depositional landforms that shape our coastal areas.

References  

  1. Fourie Jean-Pierre et al., 2015, The influence of wave action on coastal erosion along Monwabisi Beach, Cape Town, South African Journal of Geomathics, Vol. 4 (2), pp. 1 – 14
  2. Sawczyński, Szymon & Kaczmarek, Leszek. (2014). Sediment transport in the coastal zone. Technical Sciences. 17. 165-180.
  3. Wigley, R. 2011. Geohazards in coastal areas. Council for Geoscience Report Number: 2011-0066
  4. https://pmel.noaa.gov/pmel-theme/oceans-and-coastal-processes-research