Civil Engineering - Irrigation - Discussion

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).

A, B is right.

C is wrong since attracting groynes has 45-60 degree d/s.

The given answer is right.
Repealing groynes toward upstream at 30 degree.
Attractive is downstream at 60 to 70 degree.
Deflecting is 90 degree.

What is the best answer?

Ocean groynes are generally found perpendicular to the bank. So, why not A?

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.

You are right @Maria saeed.

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.