Mallorca Island, located at the western Mediterranean Sea (Balearic Sea), is the greatest of the Balearic Islands. The area of interest is located at the north-western sector of the Alcudia Bay (Can Picafort beach). Alcudia Bay has a structural origin, as it is limited by NE-SW Neogene normal faults at its margins, where Mesozoic materials outcrop.
At the subsiding sector a sand beach system with a wet zone onshore is present (Albufera d’Alcudia). On the other hand, at the stable sector sand beaches and gently rocky coast (Plio-Pleistocene eolianites) appears alternatively. The origin of the sediments is mainly Bioclastic (89%), being the lithoclastic fraction very low (11%). The grain size of the Alcudia bay sand has a 60 % of medium sand (between 0.25 and 0.5 mm), a 25 % of coarse sand (between 0.5 and 1 mm) and a 15 % of fine sand (between 0.125 and 0.25 mm).
The studied sector of coast consists on 5 km long beach (from Can Picafort to S’Oberta) with a NW-SE orientation and opened to the NE. Tidal processes are almost imperceptible and height wave do not overpasses the 4 m in the open sea. The bathymetry of the Alcudia bay is also gentle. Two independent sedimentary cells can be defined in the Alcudia Bay, a northern cell (studied area) and a southern one. Wave induced longshore transport can be considered as the most important process along the Alcudia Bay, which at the studied sector has a main SE-NW direction. Aeolian transport has also a great importance but in this case the sand dunes evolve from North to South (Servera, 1997). Thus in the studied zone the longshore sea transport has a S-N direction and the eolian one has an N–S direction.
The studied shore shows erosion and accretion at different places. The distribution of the erosion and accretion sites is mainly controlled by human constructions (dikes and harbours) together with the longshore transport and storms. The type of erosion observed at Alcudia Bay is a gradual sediment loss due to the S-N longshore transport. The biological activity is strongly related to the Posidonia Oceanica. Almost all the beings that form the sediment of the beaches live around or depend on that plant. For that reason when we reduce the Posidonia Oceanica prairies we kill the sediment factory of the Mallorca beaches. As there is not any external supply when the Posidonia Oceanica prairies are destroyed we are inducing a beach retreat.
The major function of the coastal zone is tourism and recreation. If the beach disappears the economic engine of the area will also disappear. For that reason the impacts of the beach retreat in this area will affect the inhabitants residing inland, not also those who has a house near the beach.
The adopted policy options in this area have been a limited intervention: sand renourishment of the most affected beach, the Can Picafort beach.