Caracterización y evolución del sistema playa-duna de la costa mediterránea de andalucía (España): influencia de procesos naturales y actuaciones antrópicas

Abstract

In past decades coastal, erosion related impacts on the world’s shorelines have been significantly growing due to ongoing coastal development and tourist occupation as well as to natural erosion/flooding events exacerbated by climatic change. Ocean coastlines are highly dynamic and changing environments since they show great temporal and spatial variability in response to the action of different and complex coastal processes: at an inter-annual time scales, related to seasonal wave climate variations due to temporal and spatial distributions of high latitude storms and tropical storms/hurricanes, or as a result of events with a large return period, such as the impact of very energetic storms and tsunamis, sea level rise, and variations in rivers’ sediment supplies. In order to prevent and reduce such impacts, coastal managers need to know the sensitivity of natural coastal sectors, which is related to wave energy, beach characteristics/evolution, and sea level trend as well as the potential vulnerability and economic value of the urbanized sectors. This paper shows coastal evolution and the impacts on it of coastal structures and the characterization and evolution of dune systems along the Mediterranean coast of Andalusia (Spain). For this purpose, an amount of 47 units were defined along the studied coast, and evolution rates (erosion/accretion/stability), for the period 1956-2016, quantified by using the DSAS extension of ArcGIS software. As a result, 9 units recorded accretion, 19 erosion and 19 stability and, concerning the beach surface balance, 17 units presented a positive balance and 28 a negative one and a net balance of -29,738.4 m2/yr. The analysis of coastal evolution evidenced the impact of hard structures: accretion was essentially observed up-drift of ports and groins and in correspondence of breakwaters; erosion was observed down-drift of ports and groins and in correspondence of seawalls and revetments, and at largest river deltas; and stability was observed at pocket beaches and coastal areas locally stabilized by protection structures and nourishment works. These results were used to determine the distribution of swash- and drift-aligned coastal sectors and main direction of sediment transport. Concerning the characterization and evolution of dune systems, they were mapped different type dunes’ systems as well as dune toe position and fragmentation, and human occupation and evolution from 1977 to 2001 and from 2001 to 2016. In total, they were delimited 53 dune systems along the Mediterranean coast of Andalusia, differentiating three types: Embryo and mobile dunes, grass-fixed dunes and stabilized dunes. It was observed a general decrease in dunes’ surfaces in the 1977-2001 period (-7.5 x 106 m2), linked to the increase of anthropic occupation (+2.3 x 106 m2), and dunes’ fragmentation, especially in Málaga and Almería provinces. During the 2001-2016 period, smaller changes in the level of fragmentation and in dunes’ surfaces were observed. An increase of dunes’ surfaces was only observed on stable or accreting beaches (4 out of 53 dune systems), both in natural and anthropic areas (usually up-drift of ports).