A Review of Sandbar Dynamics and River Avulsion Mechanisms

River avulsion, the sudden relocation of a river channel to a new course from the parent channel, is a geomorphic process with direct implications for floodplain evolution, ecosystem dynamics, and infrastructure vulnerability. This review article discusses how sandbar migration acts as a precursor to avulsion by altering hydraulic geometry, redirecting flow paths, modifying sediment transport patterns, and affecting the development of incipient channels. The morphodynamic evolution of sandbars, influenced by sediment supply, flow regime, vegetation, and anthropogenic influences, such as dams and sand mining, plays a central role in creating avulsion. Different methods, such as field measurements, remote sensing imagery (including multispectral, SAR, LiDAR and UAV), physics-based numerical models, machine learning, and deep learning techniques, which are used to evaluate river sandbar and river avulsion, are also thoroughly evaluated for efficacy and fit for purpose. Future research should focus on combining different data sources and creating a model that understands vegetation–sediment–flow feedbacks, sediment sorting process, anthropogenic impacts and extreme climate change impacts on channel evolution.