Hydro-morphologic Variations Induced by Bandal-like Structures for River Bank Protection

Abstract River training protects alluvial riverbanks from erosion and flood damage worldwide. This approach is crucial in sediment-laden river systems, such as the Ganges-Brahmaputra-Meghna delta and the Mekong River basin in Southeast Asia. Researchers are investigating bandal-like structures as a sustainable riverbank protection alternative. These hybrid spur dikes combine upper impermeable sections for flow deflection with lower permeable sections for sediment passage, enhancing both bank stability and navigation sustainability. This study assesses the efficacy of bandals by laboratory experiments and numerical simulations using the computational fluid dynamics (CFD) framework FLOW-3D Hydro. Laboratory experiments were conducted in clear water conditions to determine the maximum relative scour depth around these structures. Three types of bandals were used, revealing different permeability and bandal size ratios for a range of Froude numbers from 0.13 to 0.36. An impermeable spur dike model was used for comparison purposes. The study confirmed that bandal-like structures with a permeability ratio of 0.625 and a bandal size ratio of 0.75 yielded superior results, achieving 51.6% reduction in local scour around the structure compared to impermeable spurs. Furthermore, significant silt deposition was observed downstream of the bandal, in contrast to conventional spurs, which significantly reduces bank erosion. A novel optimization-based empirical equation was developed to predict the relative maximum scour depth with a correlation coefficient R 2 of 0.9791. The results indicated that bandal-like structures can effectively function for riverbank protection and the sustainability of river management and navigation, supporting the United Nations Sustainable Development Goals (SDGs).