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<p>Suspended sediment (SS) dynamics in semi-arid Mediterranean mountain catchments provide key insights into soil erosion processes and sediment transfer under flash flood conditions. requiring detailed monitoring of streamflow (Q) and suspended sediment concentration (SSC). The primary aim of this study was to investigate the temporal variability of suspended sediment concentration (SSC) and its relationship with hydrological responses in two representative headwater catchments of the Central High Atlas of Morocco, namely, Imi n Ouarg (7 km<sup>2</sup>; 1541 m a.s.l.) and Bou Azmou (2.7 km<sup>2</sup>; 2270 m a.s.l.). Event-based monitoring was conducted from September 2019 to 2022. Event-based monitoring of discharge and suspended sediment concentration was conducted from September 2019 to 2022. The results reveal marked differences in sediment dynamics between the two catchments. Bou Azmou, characterized by a smaller drainage area and a dominance of bare land (79%), exhibits highly reactive sediment behavior, with abrupt SSC peaks exceeding 120 g/L associated with short and intense flood events. In contrast, Imi n Ouarg, characterized by extensive open forest cover (87%), exhibits lower SSC magnitudes but pronounced temporal variability, with maximum concentrations reaching 127 g/L. This pattern suggests a more complex hydrosedimentary response involving sediment storage, delayed remobilization, and variable hillslope–channel connectivity. In both catchments, the majority of sediment transport occurs during high-flow conditions. confirming the dominant role of flash floods in sediment export. Low-flow periods contribute only marginally to the total sediment flux. The comparative analysis highlights the strong control of morphometry, altitude, and land use on sediment availability and transfer efficiency. Smaller and steeper catchments such as Bou Azmou favor rapid sediment flushing, whereas larger and more vegetated basins like Imi n Ouarg promote delayed and more heterogeneous sediment responses. These findings are consistent with sediment transport patterns reported in Mediterranean environments, where extreme hydrological events govern sediment fluxes. The novelty of this study lies in the establishment of a high-resolution field monitoring dataset in a data-scarce semi-arid mountain context, allowing for a direct comparison of SSC dynamics between two contrasted catchments under natural conditions. This work provides new insights into event-scale sediment processes in the High Atlas and contributes to improving the understanding of sediment responses to flash floods, which is essential for sustainable watershed management under increasing climatic variability.</p>

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Suspended sediment dynamics during flash floods in two contrasting headwater catchments of the Central High Atlas (Morocco)

  • 期刊论文

  • 发表日期：

    2026年7月23日

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  • Mimoun Goumih,
  • Mohamed El Ghachi,
  • Nadia Ennaji,
  • Lahcen Alili,
  • Amroumoussa Benmoussa,
  • Mohamed Karoual,
  • Mohamed Rizki,
  • Hasan Ouakhir

摘要

Suspended sediment (SS) dynamics in semi-arid Mediterranean mountain catchments provide key insights into soil erosion processes and sediment transfer under flash flood conditions. requiring detailed monitoring of streamflow (Q) and suspended sediment concentration (SSC). The primary aim of this study was to investigate the temporal variability of suspended sediment concentration (SSC) and its relationship with hydrological responses in two representative headwater catchments of the Central High Atlas of Morocco, namely, Imi n Ouarg (7 km2; 1541 m a.s.l.) and Bou Azmou (2.7 km2; 2270 m a.s.l.). Event-based monitoring was conducted from September 2019 to 2022. Event-based monitoring of discharge and suspended sediment concentration was conducted from September 2019 to 2022. The results reveal marked differences in sediment dynamics between the two catchments. Bou Azmou, characterized by a smaller drainage area and a dominance of bare land (79%), exhibits highly reactive sediment behavior, with abrupt SSC peaks exceeding 120 g/L associated with short and intense flood events. In contrast, Imi n Ouarg, characterized by extensive open forest cover (87%), exhibits lower SSC magnitudes but pronounced temporal variability, with maximum concentrations reaching 127 g/L. This pattern suggests a more complex hydrosedimentary response involving sediment storage, delayed remobilization, and variable hillslope–channel connectivity. In both catchments, the majority of sediment transport occurs during high-flow conditions. confirming the dominant role of flash floods in sediment export. Low-flow periods contribute only marginally to the total sediment flux. The comparative analysis highlights the strong control of morphometry, altitude, and land use on sediment availability and transfer efficiency. Smaller and steeper catchments such as Bou Azmou favor rapid sediment flushing, whereas larger and more vegetated basins like Imi n Ouarg promote delayed and more heterogeneous sediment responses. These findings are consistent with sediment transport patterns reported in Mediterranean environments, where extreme hydrological events govern sediment fluxes. The novelty of this study lies in the establishment of a high-resolution field monitoring dataset in a data-scarce semi-arid mountain context, allowing for a direct comparison of SSC dynamics between two contrasted catchments under natural conditions. This work provides new insights into event-scale sediment processes in the High Atlas and contributes to improving the understanding of sediment responses to flash floods, which is essential for sustainable watershed management under increasing climatic variability.