Etude morphodynamique d’une avant plage à barres : cas de Kalaat Andalous et Raoued, Golfe de Tunis (Tunisie, Méditerranée)

Abstract

The aim of this study is the monitoring of the morphodynamic response of a microtidal sandbars beaches under storm surge conditions. The workfield is located in the western bay of the Gulf of Tunis: Kalaat Andalous and Raoued beaches (Mediterranean Sea). The morphodynamic study was based on a sedimentological surveys completed by a detailed topo-bathymetric measurement (from 0 to-8 m in depth). The field campaigns were conducted in a south to eastern wave dominated storm condition (June 2014). The calculation of Ω parameter and surf similarity index ξ indicates that beaches are ranging from dissipative for Kalaat Andalous (Ω= 11,4 and 12,4 ψ= 0,54 and 1,52) to intermediate for Raoued (Ω= 2,7 and 12,4 ψ= 0,4 and 1,33). Sediments textural distribution of Kalaat Andalous and Raoued nearshores shows a decreasing of the grain size pattern toward seaward marked by heterogeneous zones. The coastal prism of the central bay’s area is characterized by the existence of two nearshore sandbars: 1- A crescentic inner bar (Rythmic Bar and Beach =RBB) and 2- A rhythmic transversal shaped outer bar (Transverse Bar and Rip = TBB) less uniform. The inner bar reveals an instability under the forcing of the southeast incident waves’ hydrodynamic regime. In fact, the three-dimensional shape of the sandbars reflected the morphodynamic response to the action of the summer Southeast swell. Both of the textural analysis and the nature of the sediments confirm this diagnosis.