How does polydispersity of grains affect barchan-barchan interactions?*

Barchans are crescent-shaped dunes found in several environments such as deserts, bottom of rivers, oil pipelines, and also on the surface of Mars. They belong to dune fields, where interactions between dunes of different sizes and speeds regulate the dynamics of the entire field. Previous studies reported interactions between barchans composed of monodisperse particles, but dunes in nature consist of polydisperse mixtures of grains. In this study, we investigate experimentally the binary interactions of barchans consisting of either (i) bidisperse mixtures or (ii) for each dune, different monodisperse grains. We measured both the dune morphologies and motion of individual grains as two subaqueous barchans interacted in a water channel. We observed that the interaction patterns vary with the grains forming the dunes, with new patterns arising when each barchan consists of monodisperse grains of different size. In addition, we computed the sediment flux over barchans during different interaction patterns. Some of the results shown in this presentation are reported in Assis et al., JGR:Earth Surf., 2022.