9:05 AM - 9:25 AM
[ACG48-01] Water and Sediment Dynamics in Natural Rivers: A Digital Twin Approach
★Invited Papers
Keywords:Water and sediment in rivers, turbulence, observation, Digital Twin
Many of Japan's rivers are characterized by steep gradients and rapid flow, making them prone to frequent damages by flooding. A significant factor contributing to flood damage is the occurrence of phenomena beneath the water surface, such as bridge pier collapse due to riverbed scour and levee failure due to bank erosion. Understanding these processes is crucial, yet sediment hydraulics remains a challenging area of study. Traditional approaches to investigating these phenomena involve hydraulic experiments and numerical simulations. However, integrating real-world observations with numerical models offers the potential to significantly advance our understanding of complex in-channel sediment transport processes and pave the way for digital twin development.
Recent advances in unmanned aerial vehicle (UAV) and sensor technologies, including high-precision cameras and LiDAR, enable the acquisition of high-resolution spatial data on river flow velocity and water level. The increasing use of multispectral and hyperspectral imaging techniques, often deployed on UAVs, allows for the mapping of fine sediment distribution on the water surface. Furthermore, Acoustic Doppler Current Profilers (ADCPs) provide valuable measurements of not only water flow but also sediment transport rates. Examples of the application of these technologies are presented below.
River channel processes are inherently dynamic and often involve complex, structured turbulence, including flows over micro-scale bedforms, intermittent boil formation, and flows induced by the cellular secondary currents. These flow structures are inextricably linked to sediment transport processes, exhibiting strong mutual interactions. Analysis of energy distribution along flow paths in quasi-real-scale experiments has revealed significant differences in energy gradients between flows influenced by small-scale fluvial morphology and those characterized by active sediment transport.
A comparative study of fine sediment distribution in the Brahmaputra River (Bangladesh) was conducted, utilizing both in situ measurements and observations from the Sentinel-2 satellite, which covers a river reach of approximately 100 km. Field measurements were collected from a manned vessel over several hours. The results demonstrate that fine sediment concentration is strongly influenced by local hydrodynamic conditions and exhibits a highly heterogeneous spatial distribution. For instance, lower concentrations were observed in dead water zones, such as those within and behind mid-channel bars, while higher concentrations were associated with areas of high flow velocity, including the upstream faces of bars and the main channel. These patterns are consistent with the influence of local flow dynamics on sediment entrainment and transport.
Focusing on smaller spatiotemporal scales (water depth and 10-minute intervals), the boils of the first kind were observed in certain locations within the river channel. ADCP measurements from a towed boat provided data on the flow field and sediment transport rates associated with these boils. The author presents a case study where boil formation appears to be linked to flow over micro-scale bedforms. The boils generate localized regions of intense shear stress at the bed, resulting in the entrainment of bed material and the subsequent upward transport of high-concentration sediment plumes to the water surface. These observed vertical sediment concentration profiles deviate significantly from those predicted by the Rouse distribution. Furthermore, the boils are characterized by upwelling at their core and downwelling in the downstream region. These phenomena were clearly captured by the observational data.
Recent advances in unmanned aerial vehicle (UAV) and sensor technologies, including high-precision cameras and LiDAR, enable the acquisition of high-resolution spatial data on river flow velocity and water level. The increasing use of multispectral and hyperspectral imaging techniques, often deployed on UAVs, allows for the mapping of fine sediment distribution on the water surface. Furthermore, Acoustic Doppler Current Profilers (ADCPs) provide valuable measurements of not only water flow but also sediment transport rates. Examples of the application of these technologies are presented below.
River channel processes are inherently dynamic and often involve complex, structured turbulence, including flows over micro-scale bedforms, intermittent boil formation, and flows induced by the cellular secondary currents. These flow structures are inextricably linked to sediment transport processes, exhibiting strong mutual interactions. Analysis of energy distribution along flow paths in quasi-real-scale experiments has revealed significant differences in energy gradients between flows influenced by small-scale fluvial morphology and those characterized by active sediment transport.
A comparative study of fine sediment distribution in the Brahmaputra River (Bangladesh) was conducted, utilizing both in situ measurements and observations from the Sentinel-2 satellite, which covers a river reach of approximately 100 km. Field measurements were collected from a manned vessel over several hours. The results demonstrate that fine sediment concentration is strongly influenced by local hydrodynamic conditions and exhibits a highly heterogeneous spatial distribution. For instance, lower concentrations were observed in dead water zones, such as those within and behind mid-channel bars, while higher concentrations were associated with areas of high flow velocity, including the upstream faces of bars and the main channel. These patterns are consistent with the influence of local flow dynamics on sediment entrainment and transport.
Focusing on smaller spatiotemporal scales (water depth and 10-minute intervals), the boils of the first kind were observed in certain locations within the river channel. ADCP measurements from a towed boat provided data on the flow field and sediment transport rates associated with these boils. The author presents a case study where boil formation appears to be linked to flow over micro-scale bedforms. The boils generate localized regions of intense shear stress at the bed, resulting in the entrainment of bed material and the subsequent upward transport of high-concentration sediment plumes to the water surface. These observed vertical sediment concentration profiles deviate significantly from those predicted by the Rouse distribution. Furthermore, the boils are characterized by upwelling at their core and downwelling in the downstream region. These phenomena were clearly captured by the observational data.