Interannual sea-level oscillations control on a modern berm-ridges plain in the southern Mediterranean coast, Gulf of Gabes-Tunisia

This study documents the genesis mode of modern berm-ridges plain in a microtidal environment (Gulf of Gabes, Tunisia), under the recent conjuncture of sea-level rise. Topographic measurement and diachronic technic through a set of satellite images data (1988–2017) was applied in Kastil sandy spit to enhance altimetry and shapes of the repetitive berm-ridges and swales. Accordingly, we found that the berm-ridges plain of Kastil sandy spit is marked by the annual growth of the couplet berm-ridge and swale. In this way, 32 berm-ridges and swales were built by the swash zones processes during the last three decades (1988–2017). Thus, the hydrodynamic signal is punctuated by the interannual sea-level oscillations. Higher sea levels produce vertical berm-ridges, whereas comparatively lower sea levels produce topographically lower berm-ridges, which are observed as swales. As a result the berm-ridges plain grows vertically and horizontally. The highest berm-ridge is the younger one which culminates at 73 cm above the older one. The average value of berm-crests and swales is 25 cm and reached maximum amplitude of 103 cm above the High-Water of Neap-Tide (HWNT). The swales height remains at less than 60 cm to the HWNT with an average height of 0.38 cm above HWNT. A slight variation in sea level, around 27 cm, occurs in half-yearly cycles. The berm-ridges and swales constitute a morphodynamic pattern in which the associated hydrodynamic forcing acting at regional scale is recorded at high resolution.