Suivi, observation et disposition des grains de quartz par saison dynamique et par cycle de marée sur les plages du Golfe de Guinée au niveau D'Abidjan (Côte D'Ivoire)

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The particle size distribution of the quartz from Port Bouet beach in Abidjan is monitored according to the dynamic seasons and by tidal cycle. Some sediment samples were collected monthly at high and low tide during topographic survey, others in the tidal cycle, every two or three hours at the foot of submerged stakes implanted in the foreshore. These samples show the granulometric sorting that takes place from one dynamic season to another. The grains are notably coarser during the season of weak agitation than during that of the strong agitation. The analysis of the average size of the sediments according to the cross-shore direction reveals that no part of the foreshore has a priori the largest particle size. From one year to another, during the same dynamic season, the largest size of the average grain can be met sometimes at the lower foreshore or at the upper foreshore. In a tide cycle, the grain size is constantly changing as the waves pass. These variations are not in the direction of evolution of the tide. The rise of the tide does not cause an increase in the average grain size, and, conversely, the tide descent does not lead to a decrease in average grain diameter.