Experimental study of the stability of crescent barchan shape in subaqueous dune evolution in unsteady water flow

A water tunnel experiment adopting the frequency conversion technology is conducted to investigate the evolution of subaqueous barchan dune driven by the periodic water flow. The kinematic and morphological characteristics of the barchan dune evolution are derived through the imaging processing. Results exhibit a good correlation between the dune kinematics and the periodic variation of water flow, which indicates that the unsteadiness is transmitted from the fluid phase to the sand phase with nearly no inertia. The stable crescent barchan shape under unsteady flow is found. Meanwhile, this crescent barchan shape breaks and reconstructs periodically during the variation of unsteady flow, which implies a flexible compromise between the dune system and the propelling force. This study suggests that the stability of crescent barchan shape can be robust under unsteady flow, which brings new understandings of the morphological stability of sand dune evolution.