Influence of the Water Content of Foreshore Sediments in the Tidal Morphological Construction Process: Coarse Sand and Fine Sand Facies in Port-bouët and Assouinde Coastal Sectors Case, Cote-d'ivoire

The erosion of sandy coasts has become a major concern for coastal populations, private investors and governments. In Côte d'Ivoire, several studies have been carried out to better understand the mechanisms of this hazard on coastal morphologies. So our knowledge of tidal shoreline morphologies on microtidal coasts such as those of Côte d'Ivoire reveals two trends: erosion of the foreshore near high tide, and a deepening near low tide, or a deepening near high tide and an erosion near low tide, depending on the part of the foreshore. The contribution of hydrodynamic parameters, in particular significant swell height and theoretical tide, explains these trends, although not exhaustively. Water content in sediment was analyzed to understand its impact on shoreline morphologies resulting from the action of hydrodynamic forcing. To this end, two altimetric surveys synchronized with sedimentological monitoring of the submerged foreshore in coarse and fine sand facies were carried out at Port Bouët and Assouindé on the Ivorian coast. These studies showed that erosion occurs at times of high water content, when saturation in the sediment is reached. This observation was clearly evident on coarse sand facies, but less so on fine sand facies. The fine sand facies has a greater capacity to absorb water and therefore remains less vulnerable to foreshore erosion. Granulometry is therefore a parameter that influences the morphological response of beaches.