Integrating tectonics and caesium-137 data for improved erosion modeling: A SWAT+ approach in the Raouz and Assifane watersheds, Moroccan Rif

The Moroccan Rif, edified by the convergence of the African and Eurasian plates, presents a true opportunity to study the impact of tectonic deformation on soil erosion. This study focuses on two contrasting watersheds: the Raouz watershed, characterized by steeply sloped marly formations and intense rainfall, and the Assifane one, marked by a complex mosaic of fault blocks and lithological contrasts. Employing the SWAT+ model, incorporating detailed structural analysis, we quantified sediment yield and assessed the influence of tectonic features. Results reveal distinct erosion patterns in both watersheds. In the Raouz watershed, the revised model accurately predicts high sediment yields (9.55 t ha-1year-1), concentrated in the highlands, and aligns with independent validation using Caesium-137 data, while the default model underestimates erosion. In the Assifane one, where the average erosion rate is 1.456 t ha-1year-1, high erosion rates are concentrated along the Jebha-Chrafate Fault and within the chaotic Predorsalian Formation. Our findings demonstrate the critical role of tectonics in driving erosion dynamics and emphasize the need to incorporate structural information into erosion models for accurate predictions and effective mitigation strategies in tectonically active landscapes.