A Comprehensive Picture for Binary Interactions of Subaqueous Barchans

We investigate experimentally the short-range interactions occurring between two subaqueous barchans. The experiments were conducted in a water channel of transparent material where controlled grains were poured inside, and a camera placed on the top acquired images of the bedforms. We varied the grain types (diameter, density, and roundness), pile masses, transverse distances, water flow rates, and initial conditions. As a result, five different patterns were identified for both aligned and off-centered configurations, and we propose interaction maps that depend basically on the ratio between the number of grains of each dune, Shields number, and alignment of barchans. In addition, we show experimental indications that an ejected barchan has roughly the same mass of the impacting one in some cases and that in wake-dominated processes the asymmetry of the downstream dune is large. The present results shed light on the size regulation of barchans found on Earth and other planets.