River Training Works MCQ with answer and solution

Concept

Repelling Groynes

Formula

N/A

Step-by-step solution

1. Review the question regarding repelling groynes in river training works. 2. Recall that repelling groynes point upstream at an angle of 10° to 30° to divert river flow away from the bank. 3. Select Option B as the correct choice.

Explanation

A repelling groyne is built pointing upstream (towards the direction from which the water flows) at an angle of about 10° to 30° relative to the line perpendicular to the bank. Pointing upstream forces the river current and deep erosion away from the bank toward the middle of the river, effectively protecting the riverbank from washing away.

Shortcut

To remember the orientation of river groynes, use the "Upstream Repels, Downstream Attracts" rule: - Repelling Groyne: Points UPSTREAM (against the flow) to push/repel water current away from the bank (inclined 10° to 30° upstream). - Attracting Groyne: Points DOWNSTREAM (with the flow) to draw water current toward the bank. - Deflecting Groyne: Built PERPENDICULAR (90°) to the bank.

Common mistake

A common mistake is selecting option A by confusing a repelling groyne with an attracting groyne, assuming that "repelling" means pointing downstream with the current. In reality, a repelling groyne points upstream against the flow to repel the current away from the bank, whereas an attracting groyne points downstream. Another frequent mistake is selecting option C by confusing it with a deflecting or normal groyne, which is placed perpendicular to the riverbank.