Fluvial geomorphology and historical evolution of the Var River, France: a case study of a highly anthropic Mediterranean braided channel

The Var River in southeastern France represents an example of a Mediterranean fluvial system profoundly modified by human activity. Over the past eight decades, engineering works, gravel mining, and urbanization have progressively confined and simplified the channel, while the river remains a vital water resource for the city of Nice and its surroundings.

We present a multi-temporal and multi-scale analysis of the lower Var River’s morphological evolution between 1940 and 2025. Historical aerial and satellite images (n > 50) were analyzed to quantify changes in braided index, channel confinement ratio, slope–width relationships, and channel morphology classes. A high-resolution UAV survey conducted in 2025 covered 20 km of the lower valley, producing detailed orthomosaics and digital elevation models from over 80,000 images. Additional sedimentological analyses combining terrestrial photogrammetry and laboratory measurements thoroughfully characterized grain size and lithology of fluvial landforms.

Results reveal a complex spatial pattern in channel form: the lower Var alternates between multi-thread and single-thread morphologies along its 20 km course, with transitions occurring over distances of less than one km. These abrupt shifts are linked to local confinement, engineered structures (among which weirs which underwent recent lowering), and bedload disconnection. Overall, the river has undergone strong simplification and narrowing, with active-channel reductions exceeding 60% in channelized reaches. The present morphology reflects a hybrid, fluvial state shaped by human regulation and contrasted hydrology. These findings provide new insights into the geomorphic resilience of Mediterranean rivers and inform sediment management and corridor planning for the Nice Metropolitan region, since it present the first high-resolution analysis of this fluvial corridor.