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<p>Climate conditions, fragile lithology, erodible soils, and particularly intense land-use and land-cover changes make Mediterranean mountain catchments in Morocco highly susceptible to rapid runoff generation and accelerated water erosion. Although runoff and soil erosion processes have been widely investigated across diverse natural and agricultural environments, event-scale sediment dynamics in semi-arid badland headwaters remain insufficiently documented. In this study, rainfall, runoff, and suspended sediment transport were monitored during 14 flash flood events in two headwater catchments, Tiguert and Wanmroud, located in the Middle Atlas of Morocco, between December 2021 and January 2024. Both catchments exhibit rapid hydrological responses characterized by short lag times and elevated suspended sediment concentrations, with sediment transport showing strong seasonal and event-scale variability. Sediment responses are primarily controlled by rainfall amount, maximum rainfall intensity, peak discharge, and runoff generation processes, which increase the complexity of sediment mobilization. The Tiguert catchment shows shorter event durations and mean peak discharges of approximately 0.58&#xa0;m³ s<sup>⁻¹</sup>, whereas Wanmroud exhibits longer events and markedly higher sediment indicators, including turbidity (≈ 654 NTU), suspended sediment concentration (≈ 375&#xa0;g l<sup>⁻¹</sup>), and sediment loads (≈ 5.15 t), nearly double those recorded at Tiguert, indicating enhanced sediment availability and transport efficiency. Hysteresis analysis reveals a clear dominance of figure-eight and complex loops, accounting for 79% of events in Tiguert and 86% in Wanmroud, while simple clockwise and counterclockwise patterns remain limited, suggesting multiple sediment sources and heterogeneous sediment pathways. Furthermore, sediment transport correlates more strongly with peak discharge than with rainfall intensity, particularly in Tiguert, whereas weaker relationships in Wanmroud suggest more complex and variable hydrological behaviour rather than a single-source Hortonian response. This study provides a robust event-based field dataset and a comparative assessment of runoff sediment coupling and hysteresis behaviour in fragile Moroccan badland headwater catchments, offering valuable insights into the hydrosedimentary functioning of semi-arid Mediterranean mountain environments.</p> Graphical abstract <p></p> <p>The present study investigates the dynamics of runoff and suspended sediment transport and their responses to flash flood events in two small semi-arid Mediterranean headwater catchments, Tiguert and Wanmroud, located in the Middle Atlas of Morocco. The research is based on continuous monitoring of rainfall and water levels, combined with discharge estimation through rating curves, manual sediment sampling during flood events, laboratory filtration for suspended sediment concentration, and hysteresis loop analysis. A total of 14 runoff events recorded between December 2021 and January 2024 were analyzed in order to compare the hydro-sedimentary functioning of the two catchments at the event scale.The results reveal clear contrasts in hydrological and sedimentary behaviour between the two basins. These differences are mainly related to variations in catchment morphology, lithology, slope distribution, drainage organization, and land use and land cover. Together, these factors control runoff production, peak discharge, sediment availability, and the timing and pathways of sediment transfer during flash floods. The study also highlights the importance of event-based analysis for understanding the complexity of suspended sediment responses in fragile Mediterranean mountain environments, where short-duration, high-intensity storms can generate rapid hydrological reactions and substantial sediment export. By combining field monitoring and process-based interpretation, this work provides new empirical insight into runoff-sediment coupling in Moroccan headwaters and contributes to a better understanding of hydro-sedimentary processes in semi-arid Mediterranean catchments.</p>

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Dynamic of Runoff, Suspended Sediment Transport, and Their Response to Flash Flood Events Within Two Small Mediterranean Catchments (Middle Atlas of Morocco)

  • 期刊论文

  • 发表日期：

    2026年7月1日

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  • Nadia Ennaji,
  • Mohammed Abahrour,
  • Hasan Ouakhir,
  • Mimoun Goumih,
  • Khouldia Nafia,
  • Meriem Hamid,
  • Khawla Bouzelgha,
  • Lahcen Alili,
  • Said Halouan,
  • Youness Abahrour,
  • Aicha Jamal,
  • Abdellah EL Badaouy,
  • Mohamed Rizki,
  • Mohamed Karoual,
  • Islah Yaakoubi,
  • Aqil Tariq,
  • Irfan Ur Rashid,
  • Mansour Almazroui

摘要

Climate conditions, fragile lithology, erodible soils, and particularly intense land-use and land-cover changes make Mediterranean mountain catchments in Morocco highly susceptible to rapid runoff generation and accelerated water erosion. Although runoff and soil erosion processes have been widely investigated across diverse natural and agricultural environments, event-scale sediment dynamics in semi-arid badland headwaters remain insufficiently documented. In this study, rainfall, runoff, and suspended sediment transport were monitored during 14 flash flood events in two headwater catchments, Tiguert and Wanmroud, located in the Middle Atlas of Morocco, between December 2021 and January 2024. Both catchments exhibit rapid hydrological responses characterized by short lag times and elevated suspended sediment concentrations, with sediment transport showing strong seasonal and event-scale variability. Sediment responses are primarily controlled by rainfall amount, maximum rainfall intensity, peak discharge, and runoff generation processes, which increase the complexity of sediment mobilization. The Tiguert catchment shows shorter event durations and mean peak discharges of approximately 0.58 m³ s⁻¹, whereas Wanmroud exhibits longer events and markedly higher sediment indicators, including turbidity (≈ 654 NTU), suspended sediment concentration (≈ 375 g l⁻¹), and sediment loads (≈ 5.15 t), nearly double those recorded at Tiguert, indicating enhanced sediment availability and transport efficiency. Hysteresis analysis reveals a clear dominance of figure-eight and complex loops, accounting for 79% of events in Tiguert and 86% in Wanmroud, while simple clockwise and counterclockwise patterns remain limited, suggesting multiple sediment sources and heterogeneous sediment pathways. Furthermore, sediment transport correlates more strongly with peak discharge than with rainfall intensity, particularly in Tiguert, whereas weaker relationships in Wanmroud suggest more complex and variable hydrological behaviour rather than a single-source Hortonian response. This study provides a robust event-based field dataset and a comparative assessment of runoff sediment coupling and hysteresis behaviour in fragile Moroccan badland headwater catchments, offering valuable insights into the hydrosedimentary functioning of semi-arid Mediterranean mountain environments.

Graphical abstract

The present study investigates the dynamics of runoff and suspended sediment transport and their responses to flash flood events in two small semi-arid Mediterranean headwater catchments, Tiguert and Wanmroud, located in the Middle Atlas of Morocco. The research is based on continuous monitoring of rainfall and water levels, combined with discharge estimation through rating curves, manual sediment sampling during flood events, laboratory filtration for suspended sediment concentration, and hysteresis loop analysis. A total of 14 runoff events recorded between December 2021 and January 2024 were analyzed in order to compare the hydro-sedimentary functioning of the two catchments at the event scale.The results reveal clear contrasts in hydrological and sedimentary behaviour between the two basins. These differences are mainly related to variations in catchment morphology, lithology, slope distribution, drainage organization, and land use and land cover. Together, these factors control runoff production, peak discharge, sediment availability, and the timing and pathways of sediment transfer during flash floods. The study also highlights the importance of event-based analysis for understanding the complexity of suspended sediment responses in fragile Mediterranean mountain environments, where short-duration, high-intensity storms can generate rapid hydrological reactions and substantial sediment export. By combining field monitoring and process-based interpretation, this work provides new empirical insight into runoff-sediment coupling in Moroccan headwaters and contributes to a better understanding of hydro-sedimentary processes in semi-arid Mediterranean catchments.