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Groynes are a type of seawall that is used to protect the coast from erosion. They usually consist of vertical piles with horizontal cross-pieces, and are placed perpendicular to the shoreline. This creates a wall which will trap sediment, preventing it from washing out to sea.
A groynes is a type of coastal defense structure that consists of an offshore breakwater, usually made from concrete, stone, or steel. Groynes are used to protect a coastline against erosion and storm surges. The groynes advantages are the following: They can be built quickly, they can be constructed in shallow water, and they require less material than other types of coastal defense structures.
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What is a groyne?
A groyne is a narrow strip of hard material, built out into the sea at right angles to the shoreline. Groynes are usually made from wood, concrete or stone.
The main purpose of a groyne is to stop longshore drift. This is the natural movement of sediments (sand and shingle) along a coastline.
How do groynes work?
Groyne field management is a process used to maintain or improve the performance of a coastline. It can involve construction or removal of structures, as well as changes to the seabed.
Groynes are one of the most common methods of coastal defence. They are structures built out into the sea at right angles to the shoreline.
Groynes work by trapping sediment carried by longshore drift. This builds up over time, forming a “spit” of land which extends out from the shoreline. This natural barrier protects the coastline from erosion by waves hitting it at an angle.
Over time, however, groynes can become ineffective as they become covered in sediment and no longer stick out into the water at right angles to the shoreline. They also need to be regularly maintained and repaired, which can be costly.
The benefits of groynes
Groyne is a piece of coastal defense or beach management used to protect an area of coastline from erosion. … The main purpose of a groyne is to disrupt longshore drift, the natural movement of sediments (sand and shingle) along a coastline.
The drawbacks of groynes
Groyne fields are not a recent development in coastal management. The first instance of their use dates back to the 17th century, when they were deployed in the Netherlands. Groynes are commonly used as a method of coastal engineering, and their deployment is carefully considered as part of an holistic approach to coastal management.
Whilst groynes can be an effective means of managing a coastline, they also have a number of drawbacks which must be considered as part of any decision to deploy them.
Cost – Groynes are not cheap to construct or maintain, and their presence can impact negatively on the amenity value of a coastline (e.g. by preventing the natural movement of sand).
Effectiveness – Groynes only work effectively when they are deployed as part of a wider strategy which takes into account the prevailing wind and wave conditions. They also require regular maintenance (e.g. replacement of missing or damaged stones) in order to remain effective.
Environmental Impact – The construction and maintenance of groynes can have a negative impact on the natural environment, both in terms of the disturbance caused by the works themselves and the changes to local hydrology and sedimentology which can result from their presence.
The types of groynes
Groyne is a common type of coastal management used to protect beaches from erosion. There are different types of groynes, but the most common are terminal and revetment groynes.
Terminal groynes are built at right angles to the beach, perpendicular to the coastline. They intercept longshore drift and so stop sediment moving down the beach. This causes a build-up of sediment on the upwind side of the groyne, which creates a headland. As the waves hit the headland, they break and lose energy, so there is less wave action on the beach behind the groyne. This protects that part of the beach from erosion.
Revetment groynes are also built at right angles to the beach, but they are constructed with an L-shape rather than being perpendicular to the coastline. Like terminal groynes, they intercept longshore drift but because of their shape, they do not form a headland. Instead, they allow sediment to build up along their length over time.
The design of groynes
Groyne design may be governed by regulations laid down by a statutory authority. For example, in the United Kingdom, planning permission for any groyne extending more than 20 metres (70 ft) offshore must be sought from the Crown Estate.
The design of groynes is governed by two main factors: firstly, they must be designed to resist the lateral (sideways) force of the sea, and secondly, they should not impede the longshore drift of sand along the beach. In addition, they should be robust enough to withstand being damaged and/or moved by storms.
There are several methods of constructing groynes:
— Piling: in this method, wooden, concrete or steel posts are driven into the seabed to form the base of the groyne. The posts are then connected together using wires or chains, and finally a wooden or concrete top beam is added.
— Bagging: in this method, bags filled with sand are placed on the seabed in rows to form the base of the groyne. The bags are then interconnected using wires or chains, and finally a wooden or concrete top beam is added.
— Placing: in this method, blocks of stone or concrete are placed on the seabed in rows to form the base of the groyne. The blocks are then interconnected using wires or chains, and finally a wooden or concrete top beam is added.
The construction of groynes
Groyne construction
Your revision guide gives you a general idea of how groynes work, but here we’ll go into a bit more detail about their construction.
Groynes are built from wood, concrete or stone. They are placed at an angle to the shoreline and extend out into the sea for a distance of between 20 and 100 metres.
Groynes are usually built in groups of three, with gaps of around 100 metres between each groyne. This is so that longshore drift can take place in the gaps and sediment can be redistributed along the beach.
The maintenance of groynes
Groyne maintenance is the responsibility of the local authority or landowner. The frequency of maintenance depends on the exposure of the groyne to wave action and its condition.
Groyne maintenance generally involves:
– regular inspections
– clearing debris from around the groyne
– repairing or replacing damaged timbers
– maintaining the stability of the structure
The decommissioning of groynes
The decommissioning of groynes is a complex engineering operation and it is often necessary to use several different methods to successfully remove a groyne. The most common method of decommissioning involves breaking up the structure of the groyne using hydraulic hammers attached to a excavator. The excavator then removes the broken concrete from the site.
In some cases, it may be possible to use a crane to lift the entire groyne out of the water. However, this method is not always feasible, particularly for large groynes. In these cases, it may be necessary to transport the groyne pieces by barge or other means to a suitable location for disposal.
The methods used to decommission a groyne will vary depending on the size and type of groyne, as well as the geographical location. It is important to consult with an experienced coastal engineer before attempting to decommission a groyne.
The future of groynes
Groyne management is constantly evolving as we learn more about the complex behaviour of our coastline. The design of groynes has also evolved, with some very long structures now used in situations where itufffds not possible to build out further into the sea.
Some areas are experimenting with different types of beach recharge, where sand is artificially added to the beach to replace what has been lost through erosion. This is a costly process and needs to be carefully managed to ensure that the correct type and amount of sand is used.
Itufffds also important to remember that groynes are just one part of managing our coastline ufffd other methods, such as managed realignment, are also used in some areas.
A groyne is a structure built at the shoreline of a body of water to protect it from erosion by waves. The word originates from the Scottish Gaelic word “grian-an” meaning “a high bank”. Reference: what is a groyne in geography.
