River training groynes (spurs): As commonly built for guiding and defending riverbanks, groynes are aligned in which orientations?

Introduction / Context:

Groynes (spurs) are transverse structures projecting from riverbanks into the flow to train the current, stabilize the channel, and protect the bank from erosion. Their orientation governs how they deflect or attract the flow and how sediment is distributed along the bankline.

Given Data / Assumptions:

• All options refer to conventional groyne alignments used worldwide.
• Angles are measured relative to the bank alignment.
• Objective: training/meander control and bank protection.

Concept / Approach:

Groynes can be built normal (perpendicular) to the bank, or skewed upstream (repelling groynes) or downstream (attracting groynes), commonly within ±30°. The selection depends on local hydraulics, sediment regime, and desired effect (deflecting current away from, or guiding it towards, a bank reach).

Step-by-Step Solution:

Verification / Alternative check:

Design manuals catalog several standard plan forms (T-head, L-head, hockey-stick) with the same range of orientations; site-specific modeling refines the choice.

Why Other Options Are Wrong:

• Limiting to only one orientation ignores widely used alternatives; the comprehensive answer is that all are practiced depending on site needs.
• Parallel groynes (training walls) are a different class of structures (guide bunds/levees).

Common Pitfalls:

• Choosing orientation without considering sediment transport; wrong choice can worsen shoaling or bank erosion.

Final Answer:

All of the above