12 13Coastal changes on sandy shorelines are continuous and occur at diverse spatial and 14 temporal scales. Gaining knowledge on beach change processes increases our capability 15 to manage risks affecting the increasing population living in coastal areas, especially 16 shoreline erosion. Processes and factors involved in medium-and short-term beach 17 changes depend on the morphological and dynamic characteristics of the coast. In this 18 work, the decadal behaviour of 58 sandy beaches along the 150 km long South-Atlantic 19 coast of Spain, between Guadalquivir river mouth and the Strait of Gibraltar, is analysed 20 in order to investigate the relationships between shoreline change patterns and the 21 diverse morphological and dynamic factors controlling beach evolution in the area. For 22 this purpose, georectified aerial photographs spanning the period 1956-2008 were 23 compared in a GIS environment to calculate rates of shoreline change. Short-term 24 evolution of beach profiles was also analysed in selected areas of interest. 25
Manuscript Click here to view linked ReferencesResults show that the study area exhibits a great variety of shoreline evolution trends, 26 with prevailing erosion in the northern and central sectors and stability or even accretion 27 in the southern sector. In general, sediment availability is the main factor determining 28 coastal erodibility in the area, largely conditioned by the reduction in fluvial sediment 29 supply caused by river basin regulation. Nearshore bathymetry also has a great 30 significance, as it controls wave refraction-diffraction patterns and wave energy 31 concentration on certain zones. Human interventions on the coast also represent a major 32 influence on beach erodibility in the study area. Severe detrimental effects are caused at 33 certain points by shore-normal engineering structures blocking longshore drift. 34Additionally extensive urban development in backbeach environments has a significant 35 influence on sediment budget at certain areas. 36On the basis of these results, a morphological and evolutive classification of sandy 37 beaches is proposed, taking into account the way beach morphology influences 38 erosive/accretionary processes. Rectilinear beaches and enclosed beaches typically 39show dynamic equilibrium or even accretion trends, whereas reef-supported beaches 40 tend to be dominated by erosion. Headland-bay beaches show complex evolution 41 patterns greatly influenced by local conditions, such as specific shoaling processes or 42 local winds. This classification is useful not only in forecasting general shoreline 43 behaviour in the near future, but also in selecting the most adequate type of intervention 44 when managing retreating coasts. 45 46