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What is the purpose of a groyne?
Groynes were originally installed along the coastline in 1915. Groynes control beach material and prevent undermining of the promenade seawall. Groynes interrupt wave action and protect the beach from being washed away by longshore drift. Longshore drift is the wave action that slowly erodes the beach.
What are the advantages and disadvantages of groyne?
Groynes
| Advantages | Disadvantages |
|---|---|
| Prevents longshore drift moving beach material along the coast. Allows the build-up of a beach. Beaches are a natural defence against erosion and an attraction for tourists. | They can be unattractive. Costly to build and maintain. |
Why do groynes need to be replaced?
Answer: The life span of a groyne is around 25 years. They must be replaced periodically to ensure the coastline continues to be protected. The process for removing and replacing each groyne can take up to two months.
What is a groyne in beach terms?
A groyne is an active structure extending from the shore into the sea, most often perpendicular or slightly oblique to the shoreline. Adequate supply of sediment and existence of medium-strong longshore sediment transport are major conditions of groynes efficiency.
Why is longshore drift bad?
Longshore drift can be very destructive to manmade structures. Longshore currents are affected by the velocity and angle of a wave. When a wave breaks at a more acute (steep) angle on a beach, encounters a steeper beach slope, or is very high, longshore currents increase in velocity.
What problems do groins cause?
A groin merely transfers erosion from one place to another further down the beach. Groins occasionally improve the shape of surfing waves by creating a rip current next to the rocks. The rip can be a hazard to swimmers. The rip can also divert beach sand onto offshore sand bars, thereby accelerating erosion.
What are the disadvantages of a groyne?
Disadvantages
- Short lifespan.
- Reduces recreational value of beach.
- Reduction of longshore drift can lead to higher erosion rates downdrift (terminal groyne syndrome)
- Ongoing maintenance cost.
- Using tropical woods will mean it’s unsustainable.
Why are jetties bad?
Artificial structures such as seawalls and jetties can have adverse effects on the coastal environment. Due to their perpendicular-to-shore placement, jetties can disturb longshore drift and cause downdrift erosion (As a mitigating action, sand building up along the jetties can be redistributed elsewhere on the shore.)
Why do people not like groynes?
Groynes. Wooden groynes need constant maintenance and replaced every 10 – 15 years. Helps to trap the sand as it is carried along the shore by longshore drift. Some people do not like the look of the groynes and people who like to walk along the beach don’t like having to climb up over these barriers.
How long do groynes usually last?
Wooden groynes have a lifetime of about 10-25 years; and groynes made of gabions of 1-5years.
How do groynes build up a beach?
The groynes are strategically placed at right angles along the coastline at varying points down the beach. They interrupt the water flow and capture the material, trapping it, which helps build up the beach and extend the land rather than it eroding away with the continuous tide.
What wood is used for groynes?
The Bournemouth timber groynes are constructed from high grade timber which is build in sections from horizontal planking and vertical piles. The timber used is a combination of Greenheart timber, found in northeast South America and Ekki timber found in West Africa.
How is the life of a groyne determined?
The length and spacing between the groynes is determined by the force of the waves, the strength of the longshore drift, and the amount of sediment engineers want to capture. A typical wooden groyne has a life expectancy of around 25 years.
What are the disadvantages of a groyne field?
Shoreline development for a groyne field consisting of three short groynes at a shoreline with a slightly oblique wave climate. The groyne field was initially filled with sand. The obvious disadvantages of groynes make that they are used less today than previously.
What are groynes and why are they important?
Groynes. Groynes are man-made coastal defence features that limit the effects of longshore drift, reduce erosion and encourage deposition. They usually run perpendicular to the shoreline, extending from the land, down the beach and into the sea. They are very obvious forms of coastal defense and, because they are usuallyinstalled in groups,…
How is the height of a groyne determined?
This means that the landward end of the groyne must be constructed on the coastline at the foot of the cliff/dunes and that its height at the landward end is not lower than the top of the backshore. The height of the groyne further seawards can be lower, depending on the requirements for sediment bypass, etc. Fig.2.