## 5 Discussion  
Although the Mari Ermi, Is Arutas and Maimoi beaches are located along a short and straight coastal area of about 8.5 km from north to south (Figure 1) and maintain an \(\Omega\) close to one with a reflective state, the morphological response to wave forcing differed among them, in terms of the dynamic response and the amount of mobilized sediment. Mari Ermi and Is Arutas are both characterized by very coarse sand and gravel siliciclastic sediment, whereas Maimoi is characterized also by a large fraction of biogenic carbonate sediments. Beach profile analysis revealed a major volumetric change on the Is Arutas and Maimoi beaches compared to Mari Ermi beach. The morphological changes were quite dissimilar among the studied beaches. In Mari Ermi, the changes occurred mainly along the beachface, whereas the crest of the barrier remained stable (Figures 5a and 7a). On Is Arutas beach, the rotation process seemed to be responsible for the beach morphological variability (Figures 5b and 7b), whereas in Maimoi the variability is characterized by an erosion of the beach which tends to return to the initial condition at the end of the monitoring period (Figures 5c and 7c). In this study we characterized the wave forcing, in terms of PS [53], as shown in Figure 7a-c. This allows us to represent the single storm strength and the cumulative power of storms that affected the beaches (Figure 7a-c). The cumulative curve of Ps highlighted that from early September to late October the power index of the single storm and the total power approaching the Sinis coastline was low. From late October to early March the singles storm power increased, and consequently the cumulative PS increased in slope (Figure 8a-c). From early March to May the singles storms power decreased, and consequently the cumulative storm power curve resulted in a gentler slope. Along our study area erosion and accretion of the beaches is related to the storms occurrences, in fact, major changes along the beach profiles were detected between early November and early March (Figure 7a-c). During this period, a total of 31 storms occurred. After early March 2011 the storms became less frequent and accounted for the general low value of Ps, and the profiles tended to recover the initial volumes registered on each beach (Figure 7). However, the profiles showed some morphological differences (Figure 5a-c). Wave forcing can be considered the main factor that promotes changes in beach morphology. Storms can cause severe erosion on beaches [51] and the natural recovery towards the initial situation depends on the following: (i) the wave climate, (ii) the beach characteristics [53], and (iii) the storms frequency, which can also influence the beach response [51; 53]. The beaches response to storms, single or in groups, and their recovery, are dependent on the beach characteristics and may be considered as site -specific [53]. In this context the geological constrains can be relevant on the storm beach response. The nature of the sediment, headlands, and rocky outcrops are the main factors that control the storm beach response along Sinis Peninsula. In the proximity of Sinis Peninsula, no siliciclastic sediment sources are present and this sediment can be considered relict [34]. Limited amounts of biogenic carbonate sediment are present mainly on Maimoi beach. This fraction is produced by the ecosystems that colonize the shallow inner shelf [35]. The northern beaches, Mari Ermi and Is Arutas, can be considered as deprived sediment beaches, in fact, for both the amount of siliciclastic relict sediment, mainly slight gravel and very coarse sand, prevail on the carbonate fraction (Figure 3c). The morphological variability and beach response to storms along these systems may be related to the grain size. In fact, the coarse grain size of Mari Ermi and Is Arutas beaches promote the sediment transport along the swash zone, which during severe storms can involve the whole sub-aerial beach [3].