Shoreline Changes at the Souss and Massa rivers mouths, Morocco: A five decades analysis (1970-2024)

River mouths are crucial environments for the exchange of energy and matter between land and ocean, yet they are highly sensitive to human interventions. This study analyzes the multi-decadal and seasonal dynamics of the Massa and Souss river mouths on the Moroccan Atlantic coast. Their evolution was assessed through diachronic shoreline analysis using aerial photographs and satellite images from 1970 to 2024, processed with GIS and DSAS tools. A seasonal topographic survey was also conducted in 2019–2020 on seven profiles using a total station. The results reveal contrasting trends: the Souss mouth is generally eroding, while the Massa mouth remains relatively stable with slight accretion. On a seasonal scale, topographic profiles indicate a morphological cycle of winter erosion followed by summer accumulation, maintaining a balanced sediment budget. Various natural and anthropogenic factors have shaped these changes over the past five decades. The river mouths experience intense Atlantic waves capable of eroding and redistributing sediments deposited by floods. Meanwhile, multiple upstream dams in the Souss and Massa watersheds have trapped 76.3 Mm³ of sediments, significantly reducing downstream sediment supply. Despite this, at a seasonal scale, the morphodynamic balance seems maintained by potential sand sources compensating for the decline in fluvial sediment input. These findings highlight the importance of understanding the interactions between hydrodynamic processes and sediment transport in these coastal environments. This study provides key insights for planning and managing the Souss and Massa estuaries, serving as a scientific reference for developing protection and integrated management strategies for these ecologically and biologically vital environments.