How Do Groynes Prevent Longshore Drift

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Longshore Drift and Groynes
How do Groynes prevent Longshore Drift?
By: Saksham Yadav

Longshore Drift and Groynes
To determine how groynes prevent longshore drift.
The issue:
Longshore drift influences the deposition and erosion of sediments. Waves erode the coast and transport the eroded material along the coastline. Over a period of time, the material will be deposited on a beach or form a larger feature such as a spit. Groynes are structures built at equal intervals along the coastline. Their purpose is to restrict longshore drift, preventing coastal erosion.

Figure 1 - Google Maps

About the location:
The location of the study area is Silver Beach in Kurnell Peninsula, near Cronulla. It is located in the Sutherland Shire, south of Sydney Central Business District (CBD) and just directly south of Kingsford Smith International Airport. The area also has a historical significance as it is near the landing place of Captain James Cook on the 28th of April 1770 in Botany Bay.

Figure 2 - Close up of the study area, Silver beach is located just on the border of Captain Cook Drive

Figure 3 - Captain Cook Obelisk, taken by Saksham Yadav on 25/2/14 at Botany Bay

Importance of the issue:
Longshore drift is a process by which sediments are transported from one place to another. When this process occurs, beaches, spits and sandbars are accreted over time. If the process of longshore drift is altered by factors such as stronger winds and stronger currents, beach erosion begins at a faster rate and this may result in many serious problems. The main stakeholders of longshore drift are resort owners. They rely on people to visit their resorts and enjoy the beach. However, if longshore drift erodes too much sand, it can permanently deprive sand from the area, which can also threaten structures close to the shoreline.
How the issue occurs (processes):
Longshore Drift occurs when waves hit the shoreline at an angle in a particular direction depending on the prevailing wind. The swash picks up sediments (sand) on the beach and carries it along the shore in the direction the wave is going, which is affected by the wind. Subsequently, gravity pulls the wave back in a process called backwash, occurring perpendicularly to the beach. The wave deposits its sediments, as its energy is lost. The sediments are then picked up by another wave (swash) and deposited further along the beach as the wave falls back due to gravity (backwash).
What changes have occurred over time?
The Kurnell Peninsula is an area of historical significance. Captain Cook landed there on the 28th of April 1770. An industrial area dominates Kurnell, including the Caltex Oil Refinery. Kurnell has also recently upgraded the Silver Beach area, where longshore drift is an issue. A new beach access-way has been installed to the west of the Caltex Jetty, areas of existing dune fence were removed to allow access to the new open lawn area, the existing sand dune...

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