Groynes are narrow, shore-perpendicular hard formations that retain a part of the sediment that would otherwise be moved alongshore, interrupting longshore sediment flow.
It contribute to constructing and stabilizing the beach ecosystem by doing so.
They are typically strong, long-lasting structures that are used as a hard-engineering protective strategy.
In this article you’ll learn:
- Purpose of groynes.
- Types of groynes.
- Merits and Demerits of groynes.
- Lots more.
So, if you’re ready to go with it, this article is for you.
Let’s dive right in.
What are Groynes?
A groyne is a stiff hydraulic structure erected from the coast (in the case of oceans) or the bank (in the case of rivers) to disperse wave energy or to preserve the banks from eroding by trapping sediments.
They can be made of a number of materials, such as rock armour, concrete, dolos, tetrapod’s, steel piling, and hardwood lumber.
Purpose of Groynes:
- They are often designed to alleviate erosion threats on exposed and moderately exposed sedimentary beaches.
- It manages beach detritus and keeps the promenade seawall from collapsing.
- It breaks up the waves and keeps the beach from being wiped away by longshore drift.
Types of Groynes:
They are categorised into three types:
Based on the Materials Used:
1. Wood Groynes:
Timber piles are used to construct wooden groynes. Single row or double row hardwood are commonly used since they meet the requirements.
They have limited durability, although they are inexpensive and effective in the short term.
2. Sandbag Groynes:
They are made of layered sand or earth-filled bags in the shape of a barrier intended for temporary or short-term use.
A particular sort of filter fabric is placed behind the sandbags to prevent them from sinking into the earth.
3. Rock Groynes:
They are made of huge-sized boulders and it is more durable than other materials.
They retain a significant quantity of wave energy while remaining stable in any condition.
4. Concrete Groynes:
Reinforced concrete or pre-fabricated concrete blocks are used to build concrete groynes.
It is the most durable and long-lasting structure and require a solid base and suitable soil conditions.
5. Sheet Pile Groynes:
Steel sheet piles are used to build sheet pile groynes.
Single sheet piles and double sheet pile groyne are both types.
Double sheet pile walls, on the other hand, are more durable and sturdier.
6. Rubble-mound Groynes:
They are ubiquitous coastal structures constructed of stones or particularly designed concrete components such as tetrapod’s.
Sheet piling is used within the rubble-mound groyne to increase strength.
It provide outstanding durability and stability.
Based on Permeability Characteristics:
6. Permeable Groynes:
Water can pass through the permeable groyne, although at a slower rate, it includes groyne made of wood, sandbags, and other materials.
It is appropriate when a river is carrying a specific level of suspended silt.
7. Impermeable Groynes:
Water cannot enter through the impermeable groyne.
Stones, gravel, gabions, and other materials are used to construct them because they are impermeable, and water may overflow under peak circumstances, necessitating a substantial protective layer.
Based on Height:
8. Submerged Groynes:
They are constructed in areas where the river depth is exceptionally deep.
Their submergence state fluctuates with the river’s water surface level.
Permeable materials are utilised to build these groyne, which limits flow velocity and prevents soil erosion of the top section.
9. Non-submerged Groynes:
They are constructed at a higher elevation than the maximum flood level. They are often made of impermeable materials.
Based on Functions.
10. Attracting Groynes:
They are constructed with their heads pointing downstream.
These are built at a 45-to-60-degree inclination to the bank because it is slanted downstream, the water flow will be drawn to the bank where the groyne is positioned.
The upstream side is subjected to significant attack by water flow, it should be built with adequate protection.
11. Repelling Groynes:
They are built at an angle of 60 to 80 degrees to the bank.
They oppose the flow of water towards the bank on which they are positioned.
The flow is mostly attacking the head area, so it should be constructed with powerful protections.
The sediments transported by the river settle in the silt pocket that forms on the upstream side.
They are more beneficial and commonly used for river training and embankment protection.
12. Deflection Groyne:
They are built perpendicular to the embankment and just deflect the water flow without denying it, protecting the banks locally.
They are less resilient and usually reflect rather than absorb energy.
13. Sediment Groynes:
There is a significant volume of silt transported by the river water when they are built.
This slow stream velocity enables sediments to settle.
These do not divert or reject the flow that are commonly utilized.
Advantages of Groynes:
- Longshore drift keeps beach detritus from drifting down the coast.
- Allows the construction of a beach. Beaches are both a natural barrier against erosion and a tourist draw.
- Enriched sediments can be deposited between groyne to promote healthy plant development and the growth of varied biological life at the beach’s edge.
- Because of their semi-permeable nature, they have long-term endurance and the potential to absorb some wave energy.
Disadvantages of Groynes:
- They can be undesirable. It is expensive to create and maintain.
- Wooden groynes are less durable and tend to reflect energy instead than absorb it.
- It causes regions on the downdrift sides to lose silt, accelerating erosion.
- They can further affect the shoreline by preventing longshore drift.
Also read: Gabion Wall | Weir | Retaining Wall | Culverts
At several points along the beach, the groynes are purposefully arranged at right angles.
They stop the flow of water and collect the material, trapping it, which helps to build up the beach and prolong the land rather than degrading it with the constant tide.