Human-driven coastline changes in the Adra River deltaic system, southeast Spain

The recent evolution of the Adra River delta in southeastern Spain has been reconstructed from historical maps, aerial photographs, and submarine multibeam bathymetric data. We have distinguished three main evolutionary stages whose development took place as a direct response to the main anthropic and natural influences on the river system. The first stage (4000 BC to 1872 AD) represents the natural behavior of the deltaic system with negligible anthropic influence. This long stage is characterized by coastline advance with the formation of a small asymmetric triangular delta in the natural river mouth and a typical prodeltaic deposit. In contrast, the second and third stages are characterized by anthropic interventions in the catchment and the river mouth, which heavily modified the natural dynamics of the deltaic system. The second stage (1872 AD to 1972 AD) coincided with damming of the natural river channel very close to its mouth and the construction of two successive artificial channels to deviate the river flow. The coastal dynamics changed during this second stage with erosion of the original delta and the formation of a new, asymmetrical delta at the mouth of the artificial channels. This younger eastern delta comprises two infralittoral wedges in the submarine realm, which recorded changes of lateral redistribution processes and enhanced influence of energetic events and can only be explained if the sediment supply from the river source was reduced during this period. The third stage (1972 AD to present-day) started with the damming of the trunk river in the central sector of the catchment, thus drastically reducing sediment flow to the coastal realm and triggering general erosion and coastline retreat.