Riverbank dynamics in a semi-arid fluvial environment: A study of the lower valley of Wadi Tamri (Atlantic Atlas, Morocco)

Riverbanks in semi-arid Mediterranean environments are dynamic features constantly shaped by natural factors and human interventions. Wadi Tamri’s lower valley, with its large alluvial plain, fragile terraces, and mixed marine/continental deposits, is a typical semi-arid fluvial landscape highly vulnerable to floods. This paper examines the dynamics and vulnerabilities of Wadi Tamri’s lower historic terraces and their landscape evolution from 1984 to 2024. It analyses river morphology and bank retreat in relation to sediment, vegetation, climate, and stream flow changes. It uses satellite imagery to identify vulnerable areas and assess channel/riverbank transformations in post-wet years and on the basis of field investigations. Multiple methods, including spade, aggregate, water retention, sedimentological (jar test), and clod cohesion (Slake) tests, provide an assessment of bank fragility and recession. The results show that Wadi Tamri’s lower sector is the most unstable, exhibiting natural morphodynamic changes (channel multiplication, bar development, lateral displacements) in 1983, 2010, and 2014. There was significant bank regression between 2000 and 2010 and increased stability (bars and vegetation) from 2010 to 2024. The increased stability, resulting partly from low flows regulated by the Moulay Abdellah dam upstream, provides valuable insights for managing fluvial landscapes exposed to human pressure and heightened flood/erosion risks in the study area.