Test: River Training Works - 2 - Civil Engineering (CE) MCQ

Permeable spurs or groynes do permit restricted flow through them. Permeable groynes, simply obstruct the flow, reducing its velocity and causing silt deposition. They are, therefore, best suited for river carrying huge sediment lead in suspension.

Denehy’s T-shaped groyne is a special type of groyne developed in India for protection of bank. It comprises of ordinary groyne with an extra cross groyne at the head giving it T-shape.
Hockey shaped groyne is an attracting type of groyne.

A groyne pointing downstream has the property of attracting the flow towards it and is called an attracting groyne. In attracting groynes scours holes are developed nearer the bank, as compared to those in a repelling groyne. Since such attracting groynes bring the water current as well as scour holes nearer the bank and make it more susceptible to damage, they are not used generally. The groynes are therefore, generally aligned either perpendicular to the bank or pointing upstream (repelling groyne).

Formation of successive bends of reverse order in a river may lead to the formation of a complete S curve called meander. Such a river is called meandering river.
When a river flows in two or more channels around alluvial islands, it is known as a braided river.
Deltaic river is a river which gets divided into branches before joining the sea, thus forming a Δ shaped delta.

1) High water training works ( training for discharge )
High water training works are constructed for the purpose of quick disposal of maximum flood and to protect adjoining land against damage due to floods.  It aims to provide sufficient river cross-section for stage passage of maximum flood.

2) Low water training works (training for depth)
It is undertaken with the primary purpose of providing sufficient water depth for navigation during a low flow period. Generally, spurs are constructed to contract the width of the channel and hence to increase the depth.

3) Mean water training works ( training for sediments )
It is undertaken with the primary purpose of providing efficient disposal of sediment load and bedload thus preserving the channel in good shape. It is the most important training of the three types.

A Groyne painting downstream has the property of attracting the flow towards it and is called an attracting groyne. In attracting groynes scour holes are developed nearer to the bank, as compared to those in a repelling groyne.

Groynes are embankment type structures, constructed transverse to the river flow, extending from the bank into the river. They are constructed to protect the bank from which they are extended,' by deflecting the current away from the bank. These are called repelling groynes. On the upstream side of a repelling groyne, a still water pocket is formed, where the suspended sediments carried by the river, gets deposited. For low water training or training for depth groynes can be used; Herein they contract the width of the channel to provide sufficient depth for navigation during low water periods.
In order to train the flow along a certain course guide banks are most commonly used. However groynes can also be used to deflect the flow or attract the flow.