The Geometry of Three-Dimensional River Dunes

Abstract

Dunes are ubiquitous in river, marine, desert and Martian environments. The fluid flow over mobile beds results in the evolution of dunes of different sizes and shapes. The literature on dunes concentrates more on 2D dunes, whereas dunes in natural rivers tend to be more three-dimensional complex shapes. The shape of the dune has a vital role in sediment transport. Bed load transport is estimated by assuming the dune shape as a triangle, which is inconsistent with field data. The typical profile of a 2D dune consists of stoss height, stoss angle, lee height, lee angle, and brink point. In three-dimensional dunes, crest line curvature also increases the complexity along with previously mentioned parameters. In the present study, the Parana river bed survey dataset is collected online (BedformsATM download SourceForge.net). The dataset contains bed profiles of Parana river surveyed in an area of 370 m x 1028 m with a spatial resolution of 1 m in each direction. Then, the bed profiles are de-trended such that dune geometry parameters can be determined accurately. The obtained dune dimensions are compared with predicted dune dimensions from different models available in the literature. It is observed that most of the models underpredicted the dune dimensions as their equations have simple relations with flow depth. The bed elevation profiles are decomposed using Empirical Method Decomposition methods to delineate the hierarchies. Further, a single dune in the Parana river dataset is isolated, and the data is used to fit the equation for a 3D dune shape. The dune generated from the equation correlates well with the original river dune. This equation will help us analyse the influence of 3D dune geometry on the flow field. Thus, it can be concluded that there is an increased need to study the flow over 3D dunes and their implications on turbulence and sediment transport.    Keywords: River dunes, 3D dunes, Dune Shape, EMD.