Civil Engineering - Irrigation - Discussion

Repelling groynes are built with their head towards upstream with an inclination of 60 to 80 degrees with the bank. They repel the water flow towards the bank on which it is located.

Repelling Groyne.

The head portion of repelling groynes is under the main attack by the flow. Hence, it should be built with strong protection. The sediments carried by the water gets deposited in the silt pocket which is formed at the upstream side of repelling groyne. These groynes are more advantageous than attracting groynes and are used widely for river training and bank protection.

All the above.

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.

1. Repelling groynes-(60°-80° inclination from bank, pointing upstream).

2. Attracting groynes-(45°-60° pointed downstream).

3. Deflecting groynes- (made perpendicular to the bank only deflect the flow without repelling the flow, it only gives local protection).

4. Denchey T-headed Groyne-(a special type of Groyne- in which earthen embankment projecting from a marginal bonds, T shape,spaced 800m apart ,head of the Groyne- has a slope on both sides and are heavily protected by stone).

1. Attracting Groyne-pointed downstream and at an angle of 45-60° with downstream.

2. Deflecting Groyne-pointed upstream and at an angle of 20-30° with normal of the bank.

3. Repelling Groyne-At an angle of 90° with the bank.

Beside that T shape and inverted hocky shape Groyne also placed according to uses.

So I think the answer will all the above as not mentioning the type of Groyne is.

A Groyne pointing upstream is a repelling one with a angle 10-30° (with the normal to bank).

While a Groyne pointing downstream is an attracting one with an angle 60-80° ( with the bank).

REFERENCE: IRRIGATION ENGINEERING AND HYDRAULIC STRUCTURES BY SANTOSH KUMAR.

According to Santosh Kumar book on" hydraulic structure" the gyrones generally, build are repelling types because it creates silt pack which serves the purpose so the majority of the time Gyrones build are of projected towards upstream so the right option is B.

Option c is not correct. The groynes which are built towards downstream have an oblique angle about 60° to 70°, not upto 30°. They are pointing towards downstream.

The option A and B are correct.

The groynes are generally aligned either perpendicular to bank or pointing upstream. Here written generally means normal groynes. This point to be noted. So, Only Option A is correct.

Ans B is correct because it shows that it is repelling Groyne which is designed at an angle 60 to 80 degree to upstream.

i.e. 10-30 degree normal to the river bank.

A is the correct answer.

Because groynes are the structure provided perpendicular to the flow of the river to project bank up it certain distance U/S and D/S.