Conservation approach of a front dune system through the study of its blowouts (Cala Agulla, Mallorca)

Most of the beach-dune systems in the western Mediterranean today show animportant state of fragmentation with obvious signs of erosion, largely because ofblowouts on the dune front. Blowouts were studied in the dune front of the CalaAgulla beach-dune system (Mallorca, Spain) in order to better understand andquantify the backward dune movement over the last decades. A spatiotemporalanalysis taking into account the boundary drawn by the vegetation along the first lineof dunes was carried out. The analysis was performed using GIS software ArcView,applying DSAS extension 2.0 (Digital Shoreline Analysis System). Fourteenblowouts located along a front about 600 m long were studied. For each blowout,some ecological and morphometric variables were analyzed in order to establish therelationship between the different types of blowouts. To this end, it was applied anindex Rt-v to link each morphology with the patterns shown by the existingvegetation, both herbaceous and woody. Applying the iTx index represents the linkbetween each typology and its inner topography. The results show integral recoil ofthe dune front over the last decades - the average recoil ranges from 10-20 m,although in some places exceed 20 m -. However, from 2008 to 2010 some advanceswere recorded, except at the sites that coincided with the main entrances to the beach,which suggests a direct relationship between maximum erosion and the places withhighest attendance. Blowouts were divided into 5 categories, trough blowouts beingthe most prevalent (50% of samples). Each type showed distinct morphometricfeatures and had a different relationship with the vegetal species.