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Difficulty: HardEnvironmental Hazards and Resource Management in Nigeria

Following severe coastal retreat along the Barrier-Lagoon coastline of Southwestern Nigeria, rigid concrete groynes were installed perpendicular to the shoreline. While sand accumulated on the up-drift side of the structures, beaches located further east experienced rapid sediment loss and accelerated landward erosion. What primary geomorphic process explains this unintended environmental hazard?

  1. Interruption of the eastward longshore drift, which traps sediment on the up-drift side and starves down-drift coastlines of natural sand replenishmentAnswer
  2. B
    Gravitational down-slope displacement of marine sediments triggered by localized mass wasting in mangrove mudflats
  3. C
    Displacement of the South-West Monsoon winds, which alters the local boundary between the rainforest and Guinea savanna zones
  4. D
    Reallocation of regulatory oversight from NOSDRA to NESREA, which delayed maintenance dredging operations

Answer

Interruption of the eastward longshore drift, which traps sediment on the up-drift side and starves down-drift coastlines of natural sand replenishment
Along the Barrier-Lagoon coast of Southwestern Nigeria (such as the Lagos shoreline), prevailing waves from the Atlantic Ocean approach obliquely, driving longshore drift from west to east. Constructing groynes perpendicular to the shore traps sand on the western (up-drift) side. Because the sediment supply moving down the coast is blocked, waves hitting the eastern (down-drift) side continue to carry sand away without receiving replenishment, resulting in severe accelerated coastal erosion.

Step-by-Step Solution

1
Analyze the coastal physical processes along the Southwestern coastline of Nigeria
Waves generated by the South-West Monsoon strike the coast at an oblique angle, creating a strong eastward littoral drift (longshore transport of sand).
Understanding the baseline sediment transport direction along the Nigerian coast is necessary to evaluate human intervention impacts.
2
Evaluate the structural impact of perpendicular groynes on littoral transport
Groynes act as barriers to longshore drift, causing deposition on the up-drift (western) side while preventing sand from reaching the down-drift (eastern) side.
Artificial barriers disrupt the sediment budget balance, causing downdrift beach starvation and accelerated erosion.
3
Select the option that accurately describes this coastal dynamics mechanism
The option identifying longshore drift interruption correctly explains the cause of downdrift erosion.
This directly links coastal engineering hazards with physical geography principles of wave action and sediment transport.

Key Concept

Coastal Erosion Hazards and Shoreline Management Dynamics in Nigeria
Estimated Time:2m 0s
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Topics

Environmental Hazards and Resource Management in Nigeria

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