<p>This study analyses the effect of hydrological fluctuations on urban sediments in the semi-arid Saïda watershed in NW Algeria. Droughts and intense rains modulate their physicochemical and rheological properties. Samples are collected from various hydrological contexts and characterized for particle size, organic matter (OM) content, and Atterberg limits. Rheological behavior is evaluated in the laboratory and modeled using the Herschel-Bulkley equation to explore the impact of OM on suspension cohesion. The results reveal a high temporal variability of sedimentary characteristics and transport dynamics, closely linked to rainfall regimes. With more than 65% of the sediments transported, the intermediate fraction (63–250&#xa0;µm) plays a central role in OM dynamics. This decreases from 7.32 to 3.40% during the events, suggesting a gradual depletion of labile reservoirs by erosive transport. A strong correlation (R² = 0.92) is observed between the decrease in the OM and that of the intermediate fraction. It reflects the role of OM as a privileged vector, linked to its mobility and its organo-mineral affinity. From a rheological perspective, the accumulation of OM enhances the cohesion and plasticity of the suspensions. An increase from 3.40 to 7.32% OM leads to an increase in the shear threshold (+ 25%) and the K consistency index (+ 40%). These results confirm the formation of organo-mineral bridges and increased inter-particulate cohesion. The observed non-Newtonian behavior reflects this complex microstructural evolution. These results highlight the preponderant roles of hydrological energy and OM in structuring urban sediments. They emphasize the need to integrate organo-mineral dynamics into sediment management strategies, to anticipate the risks associated with urban transportation, and to enhance the resilience of arid environments.</p>