Decadal evolution of coastline armouring along the Mediterranean Andalusia littoral (South of Spain)

Emplacement of hard coastal defence structures, such as seawalls, revetments, groins and breakwaters, or even ports, harbours and marinas, is commonly known as coastline armouring. This paper deals with coastal armouring evolution along the 546 km Mediterranean coast of Andalusia (Spain). It is based on photo interpretation and GIS tools, which have been employed to map coastal structure emplacement and evolution by analysis of 1956, 1977, 2001 and 2010 aerial photos. Additionally the coefficient of infrastructural impact K, which represented the relation between the total length of maritime structures and the length of the study coastal section, was obtained - i.e. minimal at 0.001 K < 0.1; average when 0.1 K < 0.5; maximal at 0.5 K < 1.0 and extreme, when K 1.0. In the mid 50s, coastal zones presented a very low level of armouring and the most important settlements were coastal towns and associated fishing communities. The total length of anthropogenic structures, 11 ports and a few protection structures, gave rise to K values ranging from “minimum” (with average K ¼ 0.07) to K “extreme” (K ¼ 2.5 in 8 sectors). During the 60s and 70s, the armoured coastline length increased from 42.1 (1956) to 98.2 km (in 1977). The “minimum” K value maintained the same average value (0.07) but affected 10 sectors. The “extreme” K value increased the average value to 3.6 and affected 25 sectors. The above was essentially linked to coastal tourism development under an extreme laissez-faire politico-economic regime: several ports were enlarged and new marinas constructed specially along the Costa del Sol. Induced coastal retreat processes were counteracted by progressive groin emplacement to enlarge tourist beaches and/or halt coastal erosion: 42 groins and 1 breakwater in 1977, some 8 fold increase with respect to 1956. Revetments and seawalls occupied a total amount of 7.6 km. Coastal occupation modalities from the mid 70s to 2001 were similar to the previous period. The armoured coastline length increased from 98.2 to 182.3 km, with “minimum” K values (average: 0.09) recorded in 15 sectors and “extreme” values (average K ¼ 4.7) recorded in 33 sectors. Coastal occupation and tourism development did not record significant improvements during 2001e2010 and K values recorded a small increase. Approaches used to halt beach erosion were coastal structures as coastal tourism was the main beach management target, carried out essentially by increasing beach carrying capacity without consideration of ecological and environmental aspects. In the last few decades, coastal defence policies experienced important changes based on reshaping/removal of hard structures and the realization of nourishment.