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The barrier island system that connects Jerba Island to the Tunisian coastline is composed mainly of carbonate bioclastic sands. Well-preserved tests of dead epiphytic foraminifera are abundant on the foreshore and backshore, but they are scattered and poorly preserved on the shoreface, where very fine sand-size eolian quartz, peloids, and broken bioclasts are the main components. The reason for this paradoxical pattern is that most epiphytic foraminifera are very easily removed as suspended load by storm-generated currents and concentrated on beaches, washover fans, and small eolian dunes, kilometers avay from their original life environment. Similar bioaccumulations are common in the fossil record and have often been interpreted incorrectly as prolific biocoenoses.
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A project to reconstruct 9~km of sandy beaches located in the north-eastern part of Jerba Island (Tunisia) is presented. The beaches face the Mediterranean Sea, and multiple offshore sand bars are a common feature in this area. The visible and underwater parts of the beaches have been eroded by sand losses, shoreline retreats, recurrent flooding, steepened nearshore profiles and continuosly decreased volume of offshore sand bars. Erosion and degradation of the coastal dunes have resulted from recreational developments in the area. Earlier `hard' protection measures implemented, such as seawalls, ripraps, etc., failed. Our project proposes a `soft' protection method that involves supplying the lacking sediment to 'strategic' places in the nearshore zones for the restoration of their wave-dominated dynamic equilibrium. Our recommendations for the project are based on historical data, observations, field measurements and numerical simulations, using a mathematical model of wave-seabed interactions (Boczar-Karakiewicz et al. 1987), with initial data provided by field measurements of waves, currents and morphology. The model predicts the formation of longshore bars and their site-specific dynamics in response to sequences of storm events in the local wave climate, while reproducing the observed quasi-periodicity of beach erosion and recovery. The conclusions of the project recommend the nourishment of two offshore bars and reconstruction of the beaches to a width of some 70 m (their pre-erosion state). The increased volume of the nourished bars will assure protection and stable conditions for the reconstructed beaches and prevent flooding. Boczar-Karakiewicz B., Bona J.L. and Cohen D.L., 1987. Interaction of shallow-water waves and bottom topography. In: Dynamical problems in continuum physics, mathematics and its application, J.L. Bona, C. Dafermos, J. Erickson & D. Kinderlehrer, editors, Springer-Verlag, New York, IMA Series in Mathematics and its Applications, 4, 131-176.
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