Analysing Short-Term Shoreline Changes Along the Ebro Delta (Spain) Using Aerial Photographs

Abstract

The use of aerial photographs to estimate short-term shoreline changes, i.e. coastal changes at a monthly scale reflecting seasonal changes in the underlying hydrodynamics, is presented in this paper. To achieve this a data set of seven vertical aerial photographs with a time span of four months, taken at the Ebro delta (NE Spanish Mediterranean coast) has been used. The method was applied to the analysis of very flat areas, highly dynamic coastal features, storm impacts and to the entire deltaic coast. Although the study area is a microtidal environment, obtained results of the very flat areas analysis do not recommend its use at very short time scales due to meteorological tide influences. The formation, erosion and re-formation of a spit at the river mouth was easily monitored being controlled the evolution of its length, perimeter and subaerial surface. Aerial photos permitted to identify vulnerable zones to impacts of very energetic storms by characterising breaching events along the coast (location and magnitude). Finally, when the method was applied to the entire deltaic coast, a detailed seasonal and spatial distribution of shoreline changes was obtained. The comparison of shoreline rates of change obtained from photos with that obtained from beach profiles shows that the method is reasonably accurate at least for the Ebro delta coast.