Experimental study on the stable morphology and self-attraction effect of subaqueous barchan dunes

Abstract

The evolutionary process of isolated dunes under the action of a unidirectional steady water flow is recorded from a bottom-up visual angle by optical synchronization imaging measurements. The morphological characteristics of dunes formed from different initial sand pile configurations are analyzed by an image-processing method. Results show that the trend of reproducing the crescent shape of the dune is shown in all sand piles, which is independent of the initial configuration. The triangular initial sand pile is found to be the first to stabilize to a crescent shape, whereas the square initial sand pile takes the longest time to form a stable crescent shape. This finding is essentially due to the shape effect of the triangle, which effectively reduces the amount of transverse moving sand particles. Based on the aspect ratio of the barchan dune that is stable at approximately 1, we determine that the evolution time required for the final stability of barchan dunes reproduced from different initial sand piles is approximately 200 s within the restriction of the present closed-water-tunnel experimental condition. Moreover, a dimensionless comparison of the profile curves of barchan dunes’ stable morphologies reveals a “streamwise–spanwise” dimension of the dune, which essentially synthesizes characteristic information about windward face and two horns. This “streamwise–spanwise” dimension ultimately presents the self-attraction effect of the crescent shape.