Study of morphological evolution of dune fields in Cantabria  (N. Spain) during the Anthropocene

Abstract: The beach-dune system constitutes a dynamic system in which several natural processes interact, both at short and long time scale. Beaches are important because are the source of sediment for the dunes that form at the limit of the shore and that create barriers that protect the mainland from the high energy waves and from floods. However dunes are quite fragile features because susceptible to erosion and for this reason they need particular attention and management, tasks not always easy to carry out since the factors involved are numerous. Along the Cantabrian coast, northern Spain, extended dune fields are present in correspondence with estuarine environments. In the last few decades they have experienced erosion due to natural agents such as winds, superficial water currents and river discharge and due to the anthropogenic influence, which after the Second World War started to increase, until the present. Additionally, intense erosive events such as storms occur seasonally, causing eventually damages to the infrastructures; the last remarkable events happened precisely in January and February 2014. The objective of this work is the analysis of the evolution of the surface and limits of four representative dune fields in the region of Cantabria in the northern Spain, describing first the main factors involved. The study is based on nine sets of aerial photographs and orthophotos ranging from 1956 to 2014 for each site, overlapped and elaborated through the software ArcGIS; the digital work allowed the calculation of the rates of migration for each interval of time along with the computation of the surface extent of each dune field. The results indicate that as general trend the coastline has retroceded in the last 58 years at average rates of 0.7m/y, but still exist, even within same dune fields, different behaviors, making of each site a complex dynamic system. The interpretation of the results led to the recognition of a rough conceptual model of evolution for each dune field: three out of four respond mainly to natural forces, while the other one migrates because of the anthropogenic pressure. The study here presented constitutes a rough attempt to examine the different processes that are implicated in the formation of large dune fields and, even though 58 years are not enough to delineate a precise evolution trend, it can be useful for future researches about coastal management