7. The role of beaches as a natural protection of the coast

There are three main reasons for the sea level to undergo continuous variations:

  • Atmospheric phenomena (atmospheric pressure) and sea phenomena (wind power on the sea) that cause storms.
  • Tectonic movements that cause tsunamis.
  • Planet movements that cause tides.

Planet tides are mainly due to the gravitational attraction exerted by the Sun and the Moon over the Earth, although by its proximity the Moon is principally responsible for the terrestrial tides. In the Mediterranean, as it is a small and virtually closed sea, tidal waves are negligible; however, the fluctuations of the atmospheric pressure do cause oscillations on the sea level.

Whilst high pressure makes the sea level low, in lower pressure systems the sea level rises, hence periods of instability can occur and the presence of storms is favoured. When large waves appear along with a rise of the sea level this can provoke flooding inshore.

The beach system starts at the sea bottom and the Posidonia oceanica helps make the waves break further offshore and thus reduce its impact on the coastline. Likewise, the dune system acts as a barrier preventing a possible sea level rise, accompanied by extreme storms, that can affect coastal areas. Therefore, if beaches did not exist, the effects of major storms could provoke flooding inshore.