In coastal protection terminology, a low wall constructed roughly perpendicular to the shoreline to interrupt longshore transport of sand and shingle is called a:

Introduction / Context:
Managing littoral drift is central to beach stabilization. Structures built perpendicular to the shore reduce the alongshore movement of sediment, creating updrift accretion and often downdrift erosion unless used in fields or with nourishment.

Given Data / Assumptions:

• Structure is low, relatively short, and oriented approximately at right angles to the coast.
• Purpose is to impede the travel of sand and shingle along a beach.
• Harbour breakwaters (parallel/oblique offshore) are different in function and scale.

Concept / Approach:
Groins (or groynes) are the canonical perpendicular shore structures for interrupting longshore drift. Breakwaters primarily shelter harbours by attenuating wave energy and are commonly detached or aligned parallel/oblique to shore. “Shore wall” and generic “break wall” are non-standard or ambiguous terms in this context.

Step-by-Step Solution:
Identify orientation: perpendicular to shore.Identify function: trap/interrupt longshore sediment transport.Match term: groins/groynes.

Verification / Alternative check:
Coastal engineering manuals and glossaries define groins as short, shore-perpendicular structures designed to control littoral drift.

Why Other Options Are Wrong:

• Breakwater/Break wall: primarily wave-sheltering structures, not primarily for drift interruption (though they may affect it secondarily).
• Shore wall: vague; not the standard term for drift control.
• Seawall spur: not the canonical name used in design literature.

Common Pitfalls:
Confusing groins with jetties or breakwaters; overlooking downdrift impacts of groin fields.

Final Answer:
Groins