Geomorphological Monitoring of the Sassandra River in Relation to the Buyo and SoubréHydroelectric Dams in Côte d'Ivoire

The Sassandra river, which flows in the western part of Côte d'Ivoire, is one of the most affected by hydropower developments, with three dams constructed along its course. The objective of the study was to evaluate the physical health of the Sassandra River prior to and following the construction of the Buyo and Soubré hydroelectric dams. To achieve this, satellite images from four years were selected: 1990, 2005, 2015, and 2025. Using these images and field data, mapping and remote-sensing tools were employed to determine several river–environment parameters, including riparian vegetation, width, sinuosity, width–depth ratio, slope, and the confinement index, among others. The vegetation on the east bank decreased from 72% in 1990 to 60% in 2025, with a slight recovery after 2005, while the vegetation on the west bank increased from 64% to 79%, at the expense of bare soil and cultivated areas. In terms of morphodynamics, the balance between erosion and accretion varied along the river: there was substantial accumulation upstream of the Buyo Dam, while the intermediate zone experienced increased erosion since 2005. The river’s morphology, particularly its meandering character (SI = 2 upstream; 1.4 in the highly sinuous zone; 1.15 downstream), shows an evolution influenced by the dams, with a decrease in sinuosity during the construction of the Soubré Dam, followed by recovery in 2025. The confinement index (> 1.5) and the width/depth ratio (< 12) suggest relative stability of the channel, modulated by river dynamics.