Coastal processes and harbour planning: select the correct statement about littoral drift and shoreline works.

Introduction / Context:
Littoral drift is the alongshore transport of sand driven by waves approaching the coastline at an angle. Understanding its direction is crucial for siting and designing harbours, groynes, and other coastal structures to avoid unintended sedimentation and erosion.

Given Data / Assumptions:

• Obliquely incident waves generate a longshore current and sand transport parallel to the shore.
• Harbour siting relative to this transport corridor affects sedimentation patterns.
• River mouths can modify local morphology but do not nullify littoral drift due solely to their orientation.

Concept / Approach:
The sign and magnitude of littoral drift are governed by wave direction (crest angle to shoreline), wave climate, and nearshore bathymetry. Structures placed across this path interrupt transport, causing updrift accretion and downdrift erosion.

Step-by-Step Solution:
Assess option (a): Correct—drift direction follows net wave approach relative to the shore.Assess option (b): Incorrect—river orientation does not by itself cause 'no littoral drift'; drift persists under oblique wave attack.Assess option (c): Incorrect—placing a harbour directly in the drift path without mitigation leads to sand build-up on one side and erosion on the other.Therefore, only statement (a) is correct.

Verification / Alternative check:
Coastal engineering texts relate net littoral drift direction to the predominant wave approach sector; river mouths often show spits and shoals precisely because drift interacts with the outflow.

Why Other Options Are Wrong:

• (b) Misstates the role of river direction; littoral processes continue.
• (c) Neglects well-known sedimentation and erosion patterns around structures in drift corridors.
• (d) Cannot be true since (b) and (c) are false.

Common Pitfalls:

• Confusing tidal or fluvial currents with wave-driven alongshore transport.
• Assuming artificial structures are neutral to sediment pathways.

Final Answer:
The direction of the littoral drift depends upon the direction of wave approach relative to the coastline