Waves

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Coastal Processes - Waves

Waves occur on the surface of bodies of water as swells. These features are created through pressure and friction from wind forces that blow over the surface of the sea. The energy in waves are some of the most significant forces involved in coastal processes. The size and energy of waves is influenced by many factors including the strength of the wind, the distance a wave has travelled, also known as the fetch, and how long wind has been blowing.

Waves consist of different characteristics such as length, height, propagation direction, and frequency, all of which are characteristics with limited predictability. The wave height, for example, shows us the vertical distance between the wave peak and the furrow. The wave length shows us the distance from crest to crest in the direction of propagation. The wave propagation direction refers to the direction as to where the wave is headed. The wave frequency, on the other hand, refers to the frequency of onset of these waves along coastlines.

Two physical mechanisms help control and maintain wave motion. Gravity, for one, is the restoring force that causes any displacements on the surface to return back to its equilibrium state. Kinetic energy, on the other hand, is responsible for a wave’s continuous and oscillating motion along the surface of the water.

These waves are key factors in the development of our marine environments and the subsequent breakdown thereof. For us to understand how waves affect coastal processes and our marine landscapes, we need to first understand the concept of waves as a phenomena. The following sections will explain the types of waves and the impacts of these on our marine and coastal environments.

What is the role of waves in coastal processes?

Waves are important features as they help us explain the use of energy involved in the transport and deposition of sediments. These waves allow for the transportation of sand, particles, rocks, and limestone for deposition along beaches.  

Understanding waves helps us predict and gain insight into the different coastal processes. The occurrence of climate change has moved scientists into investigating these concepts a bit more, in order to find ways of mitigating climate change and some of the damaging effects of waves..

The wave’s ability to move around the globe for thousands of kilometers is one of their key characteristics. Energy plays a significant role in how these waves develop and how waves are able to travel long distances. As energy within waves builds up, different sediments are picked up and transported. As these waves approach shorelines, they usually lose energy and drop off these sediments, thus causing deposition and build-up.

In some cases, as waves begin to get concentrated in shorelines, wave height begins to increase, and as soon as it reaches a certain height and becomes unsteady, the wave breaks and collapses, thus transferring the energy on to the coastal zones, dropping off sediments and materials in the process. However, waves also have the capability of eroding and removing sediments along the shoreline when they have enough energy to pick up these sediments and return them to the sea.

In terms of the movement of energy and waves, sand along the beach is also an important factor to look into. For instance, sandbanks continuously change in form and move because of the impacts of waves depending on their size and height. The movement of these sandbanks greatly affects how sediments and materials are transported and eroded.

Keep in mind however, that not all waves are the result of the action of winds. Some waves are of seismic origin such as tsunamis which are the result of submarine earthquakes or volcanic eruptions. These waves are usually destructive, have great lengths, and travel across the ocean at tremendous speeds. These destructive waves often damage coastlines and are considered as hazards to communities that live near coastlines.

What are the different types of waves?

Waves consist of different forms, shapes, and sizes. Each form impacts ocean processes differently because of their different characteristics.

Capillary waves

Capillary waves, also referred to as ripples, are what one notices on the ocean’s surface at the start of a breeze. These waves are characterized by short wavelengths, where surface tension is the main restoring force that dominates the wave’s motion.

Gravity waves 

Gravity waves have high wavelengths, and have gravity and inertia as the dominating forces that drive the wave’s motion. Gravity here helps restore the surface tension and prevents the wave from extending any further.

Free waves 

Free waves occur as a result of sudden impulses, and are usually influenced by friction.

These waves are characterized by their small sizes and have less significant impacts. Most ocean surface waves, except tidal waves, are examples of free waves.

Long-time waves 

Long-time waves normally last over five minutes. These well-structured waves occur because of extensive weather conditions, earthquakes, and other climate-related impacts. These long-time waves happen because of storm flows or tsunamis, for example. Gravity plays a key role in managing the waves’ large sizes.

Tides 

Tides normally happen because of the earth’s movement and gravity. These are heavily influenced by the size and distance of the earth from the moon as well as the sun. These tides greatly determine if we experience high tides or low tides. In the event of a full moon, for example, one tends to see long-term and lengthier waves.   

Standing Waves 

Standing Waves, also referred to as seiche, are normally found in enclosed areas as a free swinging or sloshing of water mass. Here the wave remains uniform without moving either horizontally or vertically.

Frequently Asked Questions 

What are Coastal Processes?  

Coastal processes include all the processes that work on coastlines, such as erosion, deposition, and transportation. These processes can allow for the build-up and breakdown of coastal areas through the use of energy found in winds or in waves. Climate and weather patterns play a key role in these processes. For example, aggressive weather increases the influences of coastal processes.

What is the role of waves? 

Waves play a major role in coastal processes as they are responsible for the transportation, build-up, and breakdown of sediments and materials along the coastline. Depending on the intensity and type of wave, processes such as deposition, erosion, and transportation of sediments can occur.

What do we mean by the transportation of sediment?   

Transportation of sediment happens when the waves, for example, pick up sediments and transport them to another area. The size and type of sediments that waves can transport are heavily influenced by the amount of energy in waves. For example, when energy drops, waves begin to release and deposit sediments.

What can we expect from climate change and waves?  

The more our weather patterns change, the more we experience storms, hurricanes, and typhoons. Subsequently, the waves experience added energy levels, and thus these waves become more intense and aggressive. These can have damaging and detrimental effects to our coastlines and the communities that reside near here.

Are waves good or bad?  

Depending on how you look at them, waves can both be good and bad. Waves, for one, help maintain the natural balance in our marine ecosystems by transporting and depositing sediments for the development of new structures. However, waves also have their own drawbacks since they have the power to erode and destroy landscapes and coastlines. Thus, it is imperative that efforts be made to understand changes in our weather systems to better predict and mitigate the damaging effects that waves could have.

References  

  1. Frost Gregory, 2011, Review of Coastal Processes and Evaluation of the Impact of the Constructed Groynes along Lady Robinsons Beach, Botany Bay, New South Wales, Australia, University of Wollongong, pp. 1 – 109.
  2. http://thebritishgeographer.weebly.com/coastal-processes.html
  3. http://www.columbia.edu/~vjd1/coastal_basic.htm 
  4. Healy T.R. (2005) Coastal Wind Effects. In: Schwartz M.L. (eds) Encyclopedia of Coastal Science. Encyclopedia of Earth Science Series. Springer, Dordrecht
  5. Dingler J.R. (2005) Beach Processes. In: Schwartz M.L. (eds) Encyclopedia of Coastal Science. Encyclopedia of Earth Science Series. Springer, Dordrecht
  6. https://www.e-education.psu.edu/earth107/node/980 
  7. 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