Geospatial analysis of the multidecadal and seasonal evolution of Sidi Rbat beach, Morocco, using GIS, topographic surveys, and digital elevation models

Abstract Sandy beaches are dynamic and vulnerable environments shaped by the interaction of hydrodynamic, fluvial, aeolian, and anthropogenic factors. This study presents the results of multi-decadal and seasonal monitoring of Sidi Rbat beach, located on the right bank of the River Massa on the Moroccan Atlantic coast. Two complementary approaches were applied. The first was a diachronic shoreline analysis over 53 years (1970–2023), based on aerial photographs and high-resolution satellite images, using the DSAS (Digital shoreline analysis system) tool within ArcGIS. The second approach consisted of the topographic monitoring of three beach profiles conducted between January 2019 and August 2021 using a total station. Two digital elevation models (DEMs), generated in summer (01/09/2020) and winter (27/02/2021), were used to produce a differential DEM to quantify sand volumes and identify erosion and deposition zones. The results showed a general erosional trend, punctuated by phases of accretion. This erosion was mainly driven by geomorphological factors including beach configuration, hydrodynamic conditions characterized by energetic Atlantic waves from the NNW, and anthropogenic influences, particularly the reduction of sediment supply following the construction of a dam in 1972. At the seasonal scale, the beach displays a classical morphodynamic cycle, with winter erosion and summer accretion, suggesting the presence of potential sediment sources such as coastal dunes, north-to-south longshore transport, and offshore sediment remobilization. DEM analysis further highlighted the strong influence of seasonal hydrodynamics on beach morphology. This study provides a solid scientific basis for understanding mesotidal beach morphodynamics along the Moroccan Atlantic coast and supports integrated coastal zone management.