What is the purpose of a groyne?

What is the purpose of a groyne?

A groyne is a shore protection structure built perpendicular to the shoreline of the coast (or river), over the beach and into the shoreface (the area between the nearshore region and the inner continental shelf), to reduce longshore drift and trap sediments.

What does a groyne look like?

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 a groyne called a groyne?

The term groyne is derived from the Old French groign, from Late Latin grunium, “snout”.

What do groynes protect?

Groynes control beach material and prevent undermining of the promenade seawall. The groyne causes the waves to break earlier and dispense the majority of their stored energy preventing the large waves breaking directly along the beach or against the shoreline itself.

What is a groyne and how does it work?

How do groynes work? When waves approach a beach at an angle, they tend to move sediment along the beach. When there is a barrier in the beach, such as a groyne, this captures sand which is moving along a coast and thus builds up a beach.

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What is the problem with groynes?

One of the biggest problems with groynes is that they can have an impact further along the coast by stopping longshore drift. By trapping the sediment, groynes starve towns and villages of sediment further down the coast.

Are groynes hard or soft?

Hard engineering – sea walls, groynes, rock armour

They are generally placed at the foot of vulnerable cliffs or at the top of a beach. They can be up to 5m high and can be flat faced or curved.

Where are there groynes?

A groyne is a long narrow structure built out into the sea from the beach to limit the movement and loss of beach material (sand and shingle). Groynes form a significant part of coastal protection around the UK coast.

What wood is used for groynes?

Two of the most popular choices are Ekki and Greenheart. However, other tropical hardwoods such as Balau and Jarrah have been used for water projects as well. Ekki is an especially great choice as it is also referred to as “iron wood” due to the strength of the material.

When were groynes first used?

The first groynes were built of wood in the 1720s, after the storms of 1703 and 1705 when Brighton’s Lower Town was destroyed. The first concrete groyne was built in 1867 at East Street. Many others have been built, and rebuilt, from then to now. But groynes were not the only protrusions to be built into the sea.

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How far apart are groynes?

demonstrates the shoreline development for the following groyne fields: three long groynes with a spacing of 600 m, i.e. 1.5 times the length of the groynes. three long groynes with spacing equal to 1200 m, i.e. 3 times the length of the groynes. three short groynes with a spacing of 600 m.

How do you know if groyne is working?

The difference in height of the beach either side of the groyne will give an indication of the effectiveness of groynes in trapping material being transported by longshore drift. The more effective the groyne the greater the distance between beach levels either side of the groyne.

How do groynes protect the beach?

A groyne functions as a physical barrier by intercepting sand moving along the shore. Sand is gradually trapped against the updrift side of the structure, resulting in a wider beach on this “supply-side” of the structure. However the downdrift beach is deprived of the sand trapped by the groyne and therefore it erodes.

What are the rock walls at the beach called?

Groins are shore perpendicular structures, used to maintain updrift beaches or to restrict longshore sediment transport.

Why are beach groins bad?

The negative impact of groins on downdrift shorelines is well understood. When a groin works as intended, sand moving along the beach in the so-called downdrift direction is trapped on the updrift side of the groin, causing a sand deficit and increasing erosion rates on the downdrift side.

How do groynes stop flooding?

Groynes are low lying wood or concrete structures which are situated out to sea from the shore. They are designed to trap sediment, dissipate wave energy and restrict the transfer of sediment away from the beach through long shore drift.

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What is the best sea Defence?

Sea Walls. These are the most obvious defensive methods. Sea walls are exactly that. Giant walls that span entire coastlines and attempt to reduce erosion and prevent flooding in the process.

Are groynes cheap?

However, they are very expensive and are accused of being ugly (not aesthetically pleasing!). Also, sea walls have been known to cause down current scarring, where waves cause more damage to unprotected areas. Groynes (as seen at Seaton Sluice!) are basically wooded fences that run at right angles to the beach.

Where in the UK are groynes used?

Groynes are positioned to trap beach material and are most effective on shingle or gravel beaches which is why the Sussex and Kent shores have an abundance. These pictures were taken on the West Sussex stretch between Littlehampton West beach and Middleton-on-Sea beach.

How do groynes cause erosion?

Groynes prevent sediment being transported to beaches further down the coast and therefore increase the amount of erosion and sediment loss at those beaches. The down drift erosion caused by the groynes may cause the need for regular maintenance and beach nourishment on the downstream side.

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