Barchan ripples under unidirectional water flows in the laboratory: formation and planar morphology

The purpose of the present study is to investigate the formation and planar shape of barchan ripples generated by laboratory unidirectional water currents and to compare the morphology with that of barchans formed by laboratory waves and flows in natural environments. A thin veneer of sand as a sediment source was placed initially at the upstream part of a recirculating flume and the change in bed configurations by the flow was recorded by a video camera. Two types of formative process were observed: one was that barchan ripples grew from barchanoid bedforms and the other was that they developed from a small aggregate of sand particles. The barchan ripples in the present test had the same characteristics in the height–width relation and in the migration speed as previously reported from the desert environment and wave‐flume studies. An examination of the planar shape of the barchans led to the result that the barchan ripples had larger values of body‐length/width, compared with those of barchans formed by water waves in the laboratory and by airflow in natural deserts. The horn‐length/width of the barchan ripples was smaller than that of barchan dunes in deserts but larger than that of barchans in oscillatory laboratory flows. Copyright © 2005 John Wiley & Sons, Ltd.