About Groynes.
So Groynes (Groin in us) is a structure made on river or ocean shores to prevent erosion of material from river bank or shore, and also it is a scour preventing hydraulic structure.Also it reduces the transportation of sediments from upstream .Groynes are made of different materials like stone, sand, concrete,timber etc, Classification of groynes on the basis of material consist of permeable groynes and impermeable groynes .The permeable groynes permits some small quantity of water to pass through them but restricts the passing of sediments on the other hand impermeable groynes restricts both water and sediment to pass through.
Classification on the basis of function Groynes serve
- Deflecting Groynes : A groyne perpendicular to the bank of the river.
- Repelling Groynes : A groyne pointing upstream of river has the property of repelling the flow away from itself are called repelling groynes and these create scours which are formed due to vertical eddies .The scours formed are away from bank and near the head of groynes.
- Attracting Groynes: A groyne pointing downstream is known as attracting groyne and these have property of attracting flow towards themselves, in this case also scours are created but are near the bank of the river
Classification based on shape of groynes
- Denehy's T-shaped Groynes :These are shaped like a T alphabet but one of the arm of T is short.
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| Denehy's T-shaped Groyne |
2. Hockey Groynes: These are shaped like a head of hockey stick but narrow.
Notes: Permeable groynes are made of large rocks, bamboo or timber and Impermeable groynes are made from rock, gravel, gabions.
- Attracting groynes point downstream, serving to attract the
stream flow toward themselves and not repel the flow toward the opposite
bank. They tend to maintain deep current close to the bank.
- Deflecting groynes change the direction of flow without repelling it. They are generally short and used for limited, local protection.
- Repelling groynes point upstream; they force the flow away
from themselves. A single groyne may have one section, for example,
attracting, and another section deflecting.
- Groynes can be built with different planview shapes. Examples are
straight groynes, T head, L head, hockey stick, inverted hockey stick
groynes, straight groynes with pier head, wing, and tail groynes.
