River-training spurs: An “attracting groyne” is aligned in which direction relative to the riverbank?

Introduction / Context:

Groynes (spurs) are transverse structures used in river training to control alignment and protect banks. Their plan orientation determines whether they repel flow away from a bank or attract it along the bank, affecting near-bank velocities and sediment deposition patterns.

Given Data / Assumptions:

• Bank protection and alignment control are desired.
• Groynes are oriented at a modest angle (often up to ~30°) to the bank alignment.
• Terminology: “Attracting” vs “Repelling” based on how the spur guides the main current.

Concept / Approach:

An attracting groyne is skewed downstream, guiding and attaching the current along the bank. A repelling (deflecting) groyne is skewed upstream, pushing the current away from the bank. Normal (perpendicular) groynes neither strongly attract nor repel and are used for local control.

Step-by-Step Solution:

Verification / Alternative check:

River-training manuals depict plan views where downstream-skewed spurs streamline flow along the bank, stabilizing alignment and flushing shoals.

Why Other Options Are Wrong:

• Perpendicular: Neutral orientation; not specifically attracting.
• Inclined upstream: Repelling, not attracting.
• Parallel or random: Do not represent standard attracting practice.

Common Pitfalls:

• Using downstream-inclined spurs where bank needs relief from high velocity; an upstream-inclined defensive spur may be preferable.

Final Answer:

Inclined downstream (attracting orientation)