Shoreline Retreat Near the Kribi Port

Start from the sediment budget. The beach is a reservoir fed by rivers and cliff erosion and drained by alongshore drift and offshore loss. Erosion begins when the outlet exceeds the supply.

The port as an interruption. A breakwater and access channel interrupt the drift of about 150,000 cubic metres a year. Sand accumulates on the up-drift side and is lost to the down-drift shore, which includes the village. Wave diffraction around the structure also bends wave crests into the sheltered lee, so wave energy is refracted onto the adjacent coast and the shoreline adjusts to a new alignment. A 45 m retreat in roughly a decade is consistent with this kind of readjustment rather than a slow background trend.

Mining as a second withdrawal. Removing 30,000 cubic metres a year from the beach and nearshore is about 20% of the annual drift. It lowers the beach profile, so storm waves reach further inland, and it removes sand before it can be moved alongshore to replace losses. Nearshore dredging can also steepen the seabed and allow larger waves to break closer to the shore.

Separating the causes. The timing helps: retreat is reported from 2012 onward, after port construction began, while mining grew after 2015. A sediment-budget calculation, comparing the drift and the mining with the observed loss rate, would be needed to apportion blame. The practical point is that both reduce the supply reaching the village, so a scheme that ignores either will fail.

Conclusion. The erosion is a down-drift supply deficit caused by a coastal engineering structure and aggravated by sand extraction, not simply the result of storms.

Rock revetment (1.2 km). It fixes the shoreline line and protects the school, ovens and houses. Capital cost is high and it needs periodic repair after storms. Critically, it does not restore the beach: the sand in front is scoured and the beach narrows, which damages the fish-smoking sites and landing places that depend on a sandy shore. It also transfers energy and erosion to the neighbouring coast, passing the problem on to other villages. Once built, people feel safe and build closer, which raises future losses.

Beach nourishment (60,000 cubic metres every four years). This adds to the sediment budget and maintains a beach, so it protects the same assets while keeping the landing and smoking sites usable. It works with the drift rather than against it, and it can be placed to feed the down-drift shore. Weaknesses: it is recurrent, so the four-yearly cost must be guaranteed; the source sand must be compatible in grain size or it will wash away quickly; and the rate of 15,000 cubic metres a year is small against a 150,000 cubic metre drift, so it slows rather than stops retreat. It also does nothing about the cause.

Groynes. Four groynes would trap sand up-drift and starve the coast down-drift, which usually harms neighbouring communities more than a revetment.

Distributional effects. The revetment protects the village at the expense of its neighbours and of the beach-based livelihood. Nourishment spreads benefit along the shore and keeps the beach as a working place.

Judgement. Nourishment is preferable because it addresses supply and keeps the beach usable, but only if the recurrent funding is secured and the sand source is approved. A revetment is a fallback for the school if retreat accelerates beyond about 10 m.

The core problem. None of the three schemes addresses the causes, so any choice is a holding operation. The decision should therefore be judged on three tests: does it protect the school and the livelihood, is it affordable beyond the first year, and does it avoid shifting harm to neighbours.

Applying the tests.

• Nourishment protects the school, keeps the beach usable for landing and smoking, and harms no neighbour. Its weakness is recurrence: 60,000 cubic metres every four years must be funded in every budget, and 15,000 cubic metres a year is modest against a 150,000 cubic metre drift. It should be chosen only with a written multi-year commitment and a verified offshore sand source.
• Revetment is a one-off product that protects the school but degrades the beach and pushes erosion along the coast. It suits a situation where the priority is a single asset and retreat is fast.
• Groynes are the least defensible here because they export the problem.

Recommendation. Fund nourishment, and treat it as one part of a package that costs little: enforce and licence sand extraction so that the 30,000 cubic metres a year is reduced and taken from approved inland or offshore sites; set a build line so no new permanent structures go up within a set distance of the shore; and agree a monitoring programme with the fishermen, who notice change first.

Who pays. The port authority is a direct beneficiary of the coast and a plausible cause of the deficit, so it should contribute the largest share under a beneficiary-pays principle. Sand miners should pay through a levy that funds part of the nourishment. The village cannot be expected to fund protection against a change it did not cause, though it can contribute labour and monitoring. If the port authority refuses, the state should treat the contribution as a condition of the operating licence.