## 2 Study Area  
The study area is located in the Sinis Peninsula, on the western coast of the island of Sardinia, western Mediterranean (Figure 1). It is included in the protected marine area (MPA) of the \"Penisola del Sinis, Isola di Mal di Ventre\", established in 1997 by the Italian Minister for the Environment. The geological setting of Sinis Peninsula includes a sequence of volcanic and sedimentary rocks (marls, sandstone and limestone), dating from the Neogene to the present [39]. In this geomorphic context, the beaches account for about 4.6 km of the total coastline length (about 8.5 km) and the rocky outcrops and spurs account for about 3.9 km. The sediments of the beaches are characterized by a coarse siliciclastic fraction and by a fine carbonate fraction [35]. The siliciclastic coarse grains, derived from the erosion of the granitic outcrops located in the Mal di Ventre Island, can be interpreted as relict sediments [34,35]. The finer biogenic carbonate sediment is produced inside the shallow coastal ecosystems and exported towards the beaches and dunes [21,35,40]. The sea floor of the Sinis Peninsula is colonized by extended meadows of the seagrass _Posidonia occanica_. Prevailing winds are mainly from the northwest (Mistral about 48% of the total annual wind frequency), due to the high Mistral wind speed and large fetch (\(\sim\)500 km) the western coastline of Sardinia exhibits the largest maxima of significant wave height in the whole Mediterranean Sea [36], and the maximum wave height can be higher than 9 m with a peak period of about 12 s [41]. The morphological variability of beach profiles collected along the southern end of the Sinis Peninsula showed that the depth of closure for this area can be located at a depth of 9 m [42]. For the same area, [PERSON] et al., 2017 [21] fixed the coastal wedge limit at a depth of 15 m.  
The studied beaches are located in the northern, central and southern sectors of the Sinis Peninsula (Figure 1b). The northern beach, named Mari Ermi (Figure 2a,d), is a beach ridge [43] about 1 km in length, the width of this system is about 60 m. The beach sediment  
Figure 1: The study area as follows: (**a**) Sardinia Island and the position of the wave buoy (red dot); (**b**) Sinis Peninsula, the continuous black rectangle indicates the multibeam acquisition area, the dashed black rectangle indicates the single-beam acquisition area; and (**c**) yearly statistics of the wave height recorded by the wave buoy available at [[http://dati.isprambiente.it/dataset/ron-rete-ondametrica-nazionale/](http://dati.isprambiente.it/dataset/ron-rete-ondametrica-nazionale/)]([http://dati.isprambiente.it/dataset/ron-rete-ondametrica-nazionale/](http://dati.isprambiente.it/dataset/ron-rete-ondametrica-nazionale/)), accessed on 30 April 2021.  
is mainly composed of coarse siliciclastic sand and gravel, with a carbonate content of about 20% [35]. The orientation of the shoreline is influenced by the presence of a rocky cage which encloses the beach to the north. This cape interferes with waves coming from the northwest, this leads to a cenulated shape in the shoreline (Figure 2a). A limited submerged sandy beach was developed only in the southern sector and is characterized by the absence of morphological features such as bars. In the northern and central sectors, wide rocky outcrops occur in the submerged domain and sediments are sporadic or absent. A patchy _Posidonia oceanica_ meadow colonizes the sea floor from a depth of about 5 m.  
The central beach (Figure 2b,e), named Is Arutas, is an embayed beach with a length of about 500 m, and about 60 m of maximum cross-shore width. The sediment is wholly siliciclastic and composed mainly of very coarse sand and gravel [3; 35; 44]. Shallow rocky outcrops occurred close to the shoreline at a depth of 2 m, these outcrops prevent the development of the submerged sandy beach (Figure 2b). [PERSON] et al. [3] inferred a rotation process for this beach. A rocky sea floor characterizes the whole submerged domain of the beach.