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<p>The Sundarbans, the world’s largest mangrove ecosystem, plays a crucial role in coastal protection, sediment regulation, and estuarine stability. Its river system is influenced by strong tides, seasonal freshwater inflow, and complex sediment–flow interactions, resulting in dynamic erosion–accretion patterns. These challenges necessitate detailed hydrodynamic studies to understand tidal behavior, sediment transport, and erosion–accretion processes that govern the long-term stability of this cyclone-prone, mangrove-dominated estuarine system. However, despite its critical ecological and socio-economic importance, comprehensive hydrodynamic studies focusing specifically on the Sundarbans River system remain limited and inadequate. This study examines how water level, velocity, bed shear stress, and discharge govern the erosion-accretion processes of the main rivers of the Sundarbans, Bangladesh. For this purpose, a hydrodynamic model developed using Delft3D was employed to simulate river-tide dynamics of the Sundarbans rivers during the dry (January) and wet (July) seasons. Five critical zones and one noncritical zone were selected based on satellite image analysis. The result shows in CZ1 a broader tidal range during the wet season (1.02–3.03&#xa0;m) compared to the dry season (1.05–2.91&#xa0;m). Although opposite flow directions are observed, the inflow and outflow patterns were found to be similar in both seasons. Shorter flood periods and higher velocity during flood tide (~ 1.07&#xa0;m/s) compared to ebb tide (~ 0.824&#xa0;m/s) in both seasons illustrate that there is flood-dominant behavior in the estuary. Higher velocities are observed in critical zones. Bed shear stress also exceeds the critical value (0.14 N/m<sup>2</sup>) in three critical zones (2.42–0.56 N/m<sup>2</sup>), leading to erosion; however, in the other two zones, accretion is observed due to bed shear stress values lower than the critical threshold. These findings provide a scientific basis for identifying erosion-prone reaches, predicting channel siltation, and supporting sustainable river management and mangrove conservation strategies in this highly dynamic environment.</p>

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Tidal simulation and effects of seasonal bed shear stress on erosion-accretion process in the Sundarbans estuarine system, Bangladesh

  • 期刊论文

  • 发表日期：

    2026年7月25日

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  • Asmaa-Ul-Husna,
  • Lamisa Muniyat,
  • K M Sakif Hasan Zisan,
  • Tasmia Hamid Zim,
  • G. M. Jahid Hasan

摘要

The Sundarbans, the world’s largest mangrove ecosystem, plays a crucial role in coastal protection, sediment regulation, and estuarine stability. Its river system is influenced by strong tides, seasonal freshwater inflow, and complex sediment–flow interactions, resulting in dynamic erosion–accretion patterns. These challenges necessitate detailed hydrodynamic studies to understand tidal behavior, sediment transport, and erosion–accretion processes that govern the long-term stability of this cyclone-prone, mangrove-dominated estuarine system. However, despite its critical ecological and socio-economic importance, comprehensive hydrodynamic studies focusing specifically on the Sundarbans River system remain limited and inadequate. This study examines how water level, velocity, bed shear stress, and discharge govern the erosion-accretion processes of the main rivers of the Sundarbans, Bangladesh. For this purpose, a hydrodynamic model developed using Delft3D was employed to simulate river-tide dynamics of the Sundarbans rivers during the dry (January) and wet (July) seasons. Five critical zones and one noncritical zone were selected based on satellite image analysis. The result shows in CZ1 a broader tidal range during the wet season (1.02–3.03 m) compared to the dry season (1.05–2.91 m). Although opposite flow directions are observed, the inflow and outflow patterns were found to be similar in both seasons. Shorter flood periods and higher velocity during flood tide (~ 1.07 m/s) compared to ebb tide (~ 0.824 m/s) in both seasons illustrate that there is flood-dominant behavior in the estuary. Higher velocities are observed in critical zones. Bed shear stress also exceeds the critical value (0.14 N/m2) in three critical zones (2.42–0.56 N/m2), leading to erosion; however, in the other two zones, accretion is observed due to bed shear stress values lower than the critical threshold. These findings provide a scientific basis for identifying erosion-prone reaches, predicting channel siltation, and supporting sustainable river management and mangrove conservation strategies in this highly dynamic environment.