11 Key Advantages and Disadvantages of Groynes |Definition &Functions of Groins |Types of Groynes
What are Groyne/Groin? | Advantages and Disadvantages of Groynes | Effects of Groynes on the Shoreline | Cost of Groynes | Problems with Groynes
What are Groyne/Groin?
A groyne or groin (in the United States) is a stiff hydraulic structure placed perpendicular to the beach from an ocean shore (in coastal engineering) or from a bank (in rivers) that stops water flow and prevents sediment transport.
It is typically constructed of wood, concrete, or stone. Groynes in the water form beaches, reduce beach erosion caused by longshore drift where it is the dominating mechanism, and aid in beach replenishment.
There is also frequent cross-shore movement, which, if it is longer than the groyne, reduces its efficiency.
Ocean groynes run primarily perpendicular to the shore, reaching into the water from the upper foreshore or beach.
A groyne can be entirely submerged, in which case it is referred to as a submerged groyne. They are frequently used in conjunction with seawalls and other forms of coastal infrastructure. Groynes also can make a shoreline appear artificial.
Groynes are normally straight lines, however they can be of varying plan view shapes, permeable or impermeable, and made of a variety of materials such as wood, sand, stone rubble, or gabion, among others.
Groynes in a river reduce the erosion process and minimize ice trapping, which improves navigation.
History of Groynes
The numerous ways and materials used for the manufacture of groins have evolved since their introduction in the 17th century. Oldest type of groyne is made entirely from wood piles or ‘staves’. In the 1880s they were still used extensively in Britain.
In 1867, the first concrete groyne was built near East Street, and it is a free promenade of 195 feet (59 meters) in length.
In recent years, groynes have now been made from steel bars and concrete, among others materials, as well as being made to look like old-growth trees.
Groynes are generally temporary structures that are removed after the beach has stabilized or after a certain period of time.
However, some have been allowed to remain in place for centuries. In Turkey groyne installations date back to the Roman Era and are still in use today as markers on our high seas coast.
There is an opinion that groynes prevent beaches from replenishing. It is known that we can build groynes at the same time with coastal sand transport systems and it will not prevent the beach from replenishing as long as the sand transport system protects the beach.
If a beach’s sand transport system is in a very good condition, then no groynes are needed and they can be potentially harmful to a local ecosystem such as in the case of endangered species (such as sea turtles).
Groynes decrease the amount of sediment carried by an eroding shoreline to a non-eroding one. This reduces downstream deposition and increases turbidity (cloudiness) of water, which hinders river navigation and fish migration.
Attracting Groynes , Deflecting Groynes & Repelling Groynes
Attracting groynes point downstream, attracting stream flow toward themselves rather than repelling it toward the other bank. They tend to keep a strong current close to the bank.
This groyne is oriented downhill, in the direction of natural flow. As a result, scour holes form, which tend to keep deep currents close to the bank.
As a result, the river’s frontal attack is directed against the upstream face and extensive protection on the downstream slope is not required.
Deflecting groynes alter the flow’s direction without resisting it. The length of a deflecting groyne is shorter than that of a repelling groyne. The river runs parallel to the bank. It only deflects the flow.
Repelling groynes face upstream, forcing the flow away from them. A single groyne may have one portion that attracts and another that deflects.
The groyne is oriented upstream at an angle of 10 to 30 degrees to the line normal to the bank. This causes the current to be deflected in a perpendicular direction to itself.
This current, when it comes into constant contact with the neighboring still water area, creates eddies and significant sweep.
The groyne’s head should be sturdy enough to withstand the swirling motion of this stream. On the upstream side, a still water pocket forms, and the suspended load brought by the river is deposited in this pocket.
Effects of Groynes on the Shoreline
Groynes are structures made of timber or stone that alter the way that sand is pushed along the coast. The effect of groynes depends on their location and orientation in relation to the shore.
They can stop sand from coming all the way to the beach, which will cause the beach to become narrower.
They can also act as breakwaters, mitigating the effects of waves. Groynes can also be constructed too far inland or close to the beach, then the beach will become wider.
Groynes have the following effects:
- They can trap migrating shorefish by creating a low-pressure zone which results in the fish being pushed upriver.
- Groynes can be a breeding ground for mosquitoes
- Groynes can affect nearby boat traffic, turning inlets into coves and causing navigation difficulties.
- Groynes alter the circulation of water, sediment and nutrients, causing an increase in the growth of algae which can block sunlight from entering the water and thus cause a decrease in the amount of available oxygen for other organisms to live off of.
- Groynes can cause a loss of beach area due to their shadowing effect, which can create a “melting effect” on the sand and sediment adjacent to the groyne.
- Groynes can interfere with public access by limiting the space available for beachgoers and tourists to safely walk along.
Different Types of groynes
In terms of structure, there are timber groynes, sheet-pile groynes, concrete groynes, rubble-mound groynes constructed of concrete blocks or stones, and sand-filled geobag groynes.
1. Concrete Groynes
Concrete groynes are made from concrete that has been reinforced with steel rebar. Because of its high tensile strength, concrete is a popular material for groynes.
Concrete groynes will remain basically unmodified for long periods of time and can include reinforcements to make them even stronger.
These are steel rods that serve as an interior skeleton around which the concrete forms. The steel absorbs a significant portion of the pressures that the concrete experiences, preventing the concrete from cracking or otherwise failing in the face of waves.
As experts typically prefabricate concrete groynes and then build them at the seashore site, these groynes appear smoother and neater than other of the alternatives.
The biggest disadvantage of concrete is its weight. Consequently, concrete groynes are only possible in regions where the earth is strong enough to support the weight of their foundations.
2. Timber Groynes
Timber groynes are made from lengths of timber that have been pre-buried in the sand at an angle although some advanced designs incorporate a vertical face for greater storage capacity.
Typically, the groynes are reinforced by buried steel rods or geotextile.
Timber is not as strong as concrete but it is cheap and easy to install . This is the least expensive option for groynes if the ground can support their weight. When timber groynes are correctly installed, they will last decades.
3. Sheet Pile Groynes
Sheet-pile groins are made from sheets of metal that have been driven into the seabed at an angle and can be single, double or multiple sheet constructions (depending on the application).
Sheet pile groynes were first developed in Australia where they have been used since the early 20th century.
They are made up of concrete that is reinforced with steel reinforcement rods and are often buried to form a watertight seal.
Steel groynes can have a variety of appearances since they can be built with contiguous sheet piling or with isolated piles that resemble wooden groynes.
While steel appears to be a tough material, it is extremely prone to corrosion in aqueous environments. The fine sand particles that circulate around a groyne may swiftly wear down steel, while the water and solutes in it induce rusting and deterioration.
Steel’s shortcomings render it unsuitable for groyne construction in most circumstances.It is usually much more effective as a reinforcement for concrete since the two materials cover each other’s weaknesses.
As previously stated, the concrete protects the steel from direct water contact, while the steel makes the concrete more durable.
4. Sandbag Groynes
Sandbag groynes are made out of sandbags. They can also be made of imported pebbles that have been dumped in front of the groyne to control shore erosion. Because they are flexible, sandbags can be used in conjunction with waves and allow for immediate changes by simply moving them around.
5. Rock Groynes
Rock groynes can be very effective in controlling shore erosion, but are only applicable for beaches where the rock is very hard.
Rock groynes are made of natural rocks that are placed in front of a beach to minimize their erosion.
Furthermore, rocks are attractive materials for erosion control applications because they remain hard even when in regular contact with water.
The disadvantage of stone groynes is that the openings that make them so effective can also enable some sediment to slip through.
Functions of Groynes
Most groynes are used to protect shorelines from erosion, but others are used to prevent ice entrapment and improve navigation. Groynes can also be used in the following ways:
Protecting land from erosion – Groynes are designed to restrain the force of waves. They can reduce large waves by 15-25% at high tide and 25-40% at low tide, depending on the location and orientation of the groyne.
Stopping ice from entering the water – Groynes that are set up perpendicular to the direction of ice floe movement (such as a wind driven floe) can be used to prevent ice entrapment, or “ice jams” from occurring.
Navigation improvements – Groynes that have been constructed as part of a larger set of navigation aids can help make it safer for boaters to navigate in a harbor or bay by reducing wave energy and turbulence.
To Create and maintain sandbars – Groynes can be designed to create a sandbar across the mouth of a river, which are more stable than natural shorelines. This is effective for preventing erosion or increasing protection from coastal storms in areas where beach erosion has already occurred.
Some Problems with Groynes
However, groins can also create beach hazards such as these:
- Blocked drainage systems can make the water’s edge more vulnerable to flooding during heavy storms.
- Debris can accumulate on shorelines that are protected by groynes, which can lead to larger problems.
- Groynes can become a serious safety hazard for swimmers who might get trapped between the groynes and the beach.
- Groynes will not stop erosion when waves are coming from an angle, like in a hurricane, and can make it worse.
- Groynes have been known to collapse.
- Groynes can prevent migratory fish from reaching their spawning grounds.
- Manmade groynes have a negative aesthetic impact on the aesthetics of a beach.
- Groynes can be a breeding ground for mosquitoes
Advantages and Disadvantages of Groynes
Advantages of Groynes
1. Navigation improvements
Groynes that have been constructed as part of a larger set of navigation aids can help make it safer for boaters to navigate in a harbor or bay by reducing wave energy and turbulence.
2. To Create and maintain sandbars
Groynes can be designed to create a sandbar across the mouth of a river, which is more stable than natural shorelines.
This is effective for preventing erosion or increasing protection from coastal storms in areas where beach erosion has already occurred.
3. Drainage System Problems
Groynes can also be used if there is concern that drainage systems could lead to flooding outside of a structure or near certain structures like houses.
4. Debris Accumulation
Groynes can be used if there is a concern that the natural movement of beach sediment may cause debris to accumulate in high-traffic areas.
5. Ice Entrapment
Groynes can reduce ice jams and ice floe formation that can create large waves and be dangerous for boaters.
6. Control Erosion and Sedimentation
Groynes are a great way to control erosion and sedimentation of a shoreline. Groynes are used to prevent beaches from eroding away or washing away during extreme beach weather conditions like storms and hurricanes.
7. Shoreline Protection
Groynes are a great way to protect houses and buildings from flooding and erosion.
8. Reduces Coastal Erosion
Groynes can be used in coastal areas to reduce beach erosion during storms and hurricanes. The waves are broken up by the groynes so that they don’t pound the shoreline as heavily, therefore reducing erosion.
Disadvantages of Groynes
While groins have their advantages, they also have some serious disadvantages with regard to storm protection when compared to other alternatives such as beach nourishment or living shorelines.
1. Impact on Marine Animals
Groynes have the possibility to be an issue for marine animals like sea turtles and whales, as debris may accumulate on a groynes structure.
The material can also get trapped underneath the groynes when there’s a strong weather event or storm.
2. Debris Accumulation
There is also a possibility of accumulating debris on groynes, especially at those with steep angles, which can be dangerous to sea turtles and other creatures that may swim close by nearby areas.
3. Construction and Maintenance
There is always a possibility that a groyne installation will fail, especially in areas with high wave energy.
Re-breakout of beach erosion may occur during the installation of groynes, and extreme weather conditions such as storms can cause too much breakage of groynes down the incline.
Groynes can also be hard to monitor for changes in storm activity so that adjustments or replacement can be made in time to prevent erosion and shoreline damage.
4. Storm Damage-
Groynes are a great way to protect houses and buildings from flooding and erosion, but there is always the possibility that a large storm could destroy a groyne or cause a significant amount of damage to the area surrounding it.
5. Scared Wildlife
There is also the possibility that wounded animals may run into groynes in areas where they have been injured by the storm or during their migration.
Costs of Groynes on the Shoreline
The cost of a groined beach can vary due to location, materials used to build it, and other factors. The cost of a groined beach depends on site specific factors and is factored into long range planning.
Groynes can be expensive to construct. A groyne constructed from rockcrete can cost up to $20,000 depending on the complexity of construction.
Groynes are often installed at 200-metre intervals, thus they are not required all down the beach. Each groyne costs between $7000 and $20000, depending on its material and length.
1. What are groynes and what their main purpose?
Groynes are a system of posts that extend outward from the shoreline in the ocean, and they are used to support the shoreline soil by preventing its shifting or erosion during heavy winds or storms.
Without groynes, the coastline can potentially shift and change over time; they are a great way to protect the property, plants, and infrastructure like roads and houses.
Groynes also help trap sand from going inland, and this helps to keep the shoreline sand replenished.
2. Why are groynes constructed?
Groyne is a commonly used coastal engineering design and for preventing coastal erosion. It can be constructed from rock, rubble, and concrete, or earthy materials and then anchored at both ends.
Groyne are also used to form a baffle to divert the erosive currents away from the coast. The most effective groynes are the ones that are a bit clever, and their design require innovation.
Groyne often are constructed onshore, but some groynes are made to be floating ones. This kind looks more natural when positioned close to the shoreline.
3. How do groynes work?
The groynes are constructed in such a way that they can withstand a certain amount of waves from the sea and then they are installed perpendicular to the coastline.
They are placed every certain distance to provide support to the vulnerable areas of the coastline.
When placed correctly, groynes can slow down the flow of water toward the shoreline and also trap some sand and keep it there.
This helps preserve your sand structure, beach, and shoreline while helping your property stay protected against any severe storms or hurricanes that may come through your area.
4. What are the main materials used in the construction of groynes?
There are many materials that can be used to build a groynes including granite, concrete, and cobbles.
The material used is dependent on location, requirements, and other factors.
5. Where are the best places to install groynes?
Groynes can be constructed at many different locations and there is no right or wrong place to construct them.
They can be installed onshore or offshore, depending on your location and the specific requirements of the groyne system.
Groynes can be installed on the sand bank, beach, or coastal roadways. The type of groynes you use will depend on your specific location and what your needs are.
6. How do I build groynes?
There is a protocol and guidelines that must be followed when constructing groynes to ensure their effectiveness and longevity for future generations. These guidelines include:
– Pre-existing groyne structures should not be removed unless they are causing damage to the shoreline. It is recommended to remove these groyne structures and install the new one.
– Groynes must be constructed with a slope that can withstand the pressure of waves even during a storm. The slope is mostly constructed in such a way that it can withstand up to 50 years of wave erosion without being disturbed.
– Horizontal and vertical concrete sections should be used to construct the groyne structure. The horizontal sections should extend at a certain angle to the shoreline and then come together to form a larger structure.
– Groynes can be installed onshore or offshore, but it is usually recommended that they are placed onshore because this is usually less expensive and does not require much maintenance.
– When constructing groynes, it is advisable for them to be constructed perpendicular to the coastline where wave energy can have an impact on the coastline.
– Groynes can be installed as a single structure or they can be connected to create more complex systems.
7. Are groynes environmentally friendly?
Yes, groynes are very good for the environment because they help trap sand, and this helps prevent erosion and the possibility of wildlife being hurt by the erosive currents.
They also help replenish beach sand in shorelines that have a shortage of it.
8. What are the pros and cons of groynes?
The biggest advantage of using groynes is that it can prevent erosion to your property, beach, and the local environment. Groynes also help protect your property from hurricanes and storms.
The only disadvantage of groynes is that it is a bit expensive to construct, but this is usually taken into consideration when planning for long range projects.
9. Are groynes effective?
Yes, groynes are very effective for protecting your property, beach, and the local environment. Groynes also help slow down erosion and protect shorelines from being eroded by water. The most effective groynes are those that are a bit clever.