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These are also called spurs.

Groynes are suitable in guiding the river flow,promoting scour, depositing of sediment where desired and traping the sediment load to build up new river banks.

spurs are suitable and hence more widely used in river training structures.

Functions of groynes:

These are used for training a river along a desired course by attracting,deflecting or repelling the flow in the river channel.

Protection of river bank is done with the help of  groynes by keeping the flow of water away from the bank.

These are used to silt up the area in the vicinty of the spur by creating a slack flow.

These are used to contract the width of river to increase the depth of flow for navigation.

Classification of groynes :

Classification based on methods and materials of construction

Permeable groyne

Impermeable groyne

2. Classification based on height of groynes w.r.t. Flood level  a. Submerged groyne   b. Non-submerged groyne     3. Classification based on function groyne serves   a. Atrracting groyne   b. Deflecting groyne   c. Repelling groyne   d. Sedimenting groyne   4. Special type of groynes    a. Denehey's T-headed groyne   b. Hockey type groyne  # Difference between Atrracting and repelling groynes: Repelling groyne :

Repelling groyne points towards upstream direction at an angle of 10 to 30 degree to the line perpendicular to the bank.

The head of a groyne causes the current to be deflected in a direction nearly perpendicular to itself.

The current coming into contact with still water are adjacent to the groyne causes vertical eddies and deep scour.

A still water pocket is formed on upstream and the suspended load that is brought by the river gets deposited in this pocket.

Attracting groynes :

Attracting groyne points downstream in the direction of flow.

This causes scour holes to form closer to the bank.

Attracting groyne bears the frontal attack of the river on its upstream face.

Hence, the upstream face has to be adequately strong.

Comparatively less heavy protection is required on the downstream slope.

Deflecting groynes :

A deflecting groyne is generally taken in a river perpendicular to the bank to only deflect the flow without repelling the flow.

Deflecting groynes have a shorter length than repelling groyne.

Deflecting groyne gives only local protection.