Journal of Geophysical Research: Earth Surface

Cover image for Vol. 120 Issue 8

Impact Factor: 3.426

ISI Journal Citation Reports © Ranking: 2014: 19/175 (Geosciences Multidisciplinary)

Online ISSN: 2169-9011

Associated Title(s): Journal of Geophysical Research

Physics-based model portrays midriver island formation

From the Amazon and the Brahmaputra to Russia's Lena, Brazil's Negro, or South America's Paraná River, many of the world's largest rivers share a number of important characteristics: they are long, they are wide, they carry high volumes of water down a course with a shallow slope, and their flows are broken up by sand bars and small islands. Despite these broad similarities, sediment dynamics related to the formation of sand bars and islands in large, branching rivers can vary markedly from one to the next. A number of processes affect the formation and stability of midstream islands, such as the rate of riverbank erosion, the hydrologic regime (the long-term variability of the river's flows), and the colonization and growth rates of stabilizing vegetation. Although researchers have previously used reduced-complexity models to study river island dynamics, Nicholas et al. describe a new physics-based, two-dimensional morphodynamic model that realistically simulates branching river dynamics over large distances and long time scales.

The new model uses representations of fluid flow, sediment transport, riverbank erosion, floodplain processes, and vegetation colonization to simulate sand bar and island evolution in large branching rivers. Through a series of runs the authors adjusted model parameters, such as the grid size and properties of the river inlet, and physical characteristics, such as sediment size, river slope, and flood regime, to test the skill of their model in simulating large branching rivers. They found that the model is able to accurately represent the shape and dynamics of sand bars and islands and to provide new insight into the differences in large river behavior seen in nature.

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