Combination of Multi-source Data and Multi-application Models to Develop a Methodology as a Qualitative Study for Beaches with very High Spatial Resolution
Résumé
Shoreline change at various spatial and temporal scales on sandy beaches depends on coastal morphology and dynamics. However, anthropogenic activity has changed the way in which coastal geomorphology influences the trend of beach erosion processes. Coastal responses to the different influencing factors are important for decision makers to manage the risks in a sustainable coastal development framework. This paper discusses a methodology based on two complementary approaches; the combined use of satellite imagery, GIS, DSAS statistical methods and a mineralogical and granulometric characterization of beach sediments by analyzing the spatial evolution of sand characteristics. In this context, we sought to identify from a geomorphological, sedimentological and hydrodynamic viewpoint the factors affecting the central zone of the Algerian coastline by the beach and to evaluate the impact of developments on their evolution and balance. For this purpose, a 17-year historical time series on the shoreline is analysed, in order to obtain recent evidence of erosion/accretion trends. We used mathematical morphology to transform RGB satellite images of very high spatial resolution into shorelines. For granulometric changes and mineralogical composition of beach surficial sediments, a sampling campaign was carried out for one beach along 17 profiles perpendicular to the shoreline. Thus, we monitored the trace metal concentrations by X-ray diffraction. The results show that the study area exhibits a wide variety of shoreline trends. This study showed that there is a concordance between the distribution of wave energies and the coastline evolution. The results relating to the granulometric indices and their distributions showed that they are generally medium-sized sands, well classified and almost symmetrical in the eastern sector of the beach and mixed facies in the western sector. However, variability in the spatial distribution of sand grains highlights the combined effect of hydrodynamic agents and sediment sources. The evidence of sediment dynamics and the statistical study of heavy metals corroborate the results both qualitatively and quantitatively, allowing us to identify coastal erodibility in the area.