<\/p>\n\n\n\n
The longshore drift pattern is based on the identification of four cells, each of which is defined by an accretion zone (spits, gulf and Roustan mouth) supplied by a zone undergoing erosion (May and Tanner, 1973; Stapor, 1974; Carter, 1988; Komar, 1998). While longshore sediment transport is the major process reshaping the Rh\u00f4ne delta coastline, cross-shore processes also exist, but these cannot be quantified using shoreline change analysis. The cell definition pattern presented here is based on the pattern of evolution of the Rh\u00f4ne delta. However, it is confirmed by simulations of longshore sediment transport using empirical equations (Sogreah, 1995; Kulling, 2017).<\/p>\n\n\n\n
The easternmost cell (CEL1<\/strong>) is located east of the Grand Rh\u00f4ne, where the prevailing sediment transport is eastward (fig. 1). It is bounded on its western side by the mouth of the Rh\u00f4ne, and on its eastern side by the La Gracieuse spit. This cell is thus fed by the present-day inputs of the Rh\u00f4ne (active source) and by the erosion of the fossil delta\u00efc lobe of P\u00e9goulier (Suanez, 1997; Suanez et al.,<\/em> 1998).<\/p>\n\n\n\n The second cell (CEL2<\/strong>) also shows a general direction of transport from west to east, and extends from Ste-Anne lagoon as far as Grau de Roustan (fig. 1). Although the shoreline retreat in this zone contributes to the supply to Pi\u00e9manson beach, part of the eroded material is stored in the vicinity of the Roustan prodelta, considered as an important sediment sink (Suanez et al.,<\/em> 1998) The limit between cells 2 and 3, located generally near Ste Anne lagoon, is explained by a reversal of the longshore drift along with sediment transport as a result of refraction of swell on the fossil deltaic lobe of the Bras de Fer (Sabatier, 2001).<\/p>\n\n\n\n The third cell 3 (CEL3)<\/strong> extends from Ste Anne lagoon in the east as far as the Petit Rh\u00f4ne in the west (fig. 1). This cell is made up of a central part subject to accumulation (spit and gulf of Beauduc), fed in the east by the retreat of the beaches and erosion of the fossil sub-delta of the Bras de Fer, and in the west by erosion of the beaches in the Saintes-Maries-de-la-Mer sector. Thus, drift convergence associated with the two eroded sectors results in an important sediment sink in the very centre of the delta. Sediment supply to Gulf of Beauduc via the Petit Rh\u00f4ne is extremely limited, being dependent on the very weak sand inputs of this arm (Arnaud-Fassetta, 1996, 1997; Arnaud-Fassetta et al.,<\/em> 2003).<\/p>\n\n\n\n To the west of the Petit Rh\u00f4ne, the fourth cell (CEL4<\/strong>) is defined by a dominant sediment transport directed towards Espiguette spit (fig. 1). As seen on the littoral of Faraman, the opposite sediment transport directions in cells 3 and 4 can be explained by the divergence of the longshore drift related to refraction of swell on the prodelta of the Petit Rh\u00f4ne (Sogreah, 1995; Sabatier, 2001). The sector in erosion from the Petit Rh\u00f4ne to Baronnets contributes to sandy inputs to the spit, which may also be considered as a sand sink (Blanc, 1977; Sabatier and Raivard, 2002).<\/p>\n\n\n