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

Abstract

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

Complex systems in aeolian geomorphology

“…The confusion of the present state is exemplified by a recent study that explicitly compares the dune models of Werner and Nishimori with surface (impact) ripples in a wind tunnel experiment (Hatano et al, 2004). Although Endo et al (2005) have recognised differences in shape between subaerial dunes and current ripples, other quarters believe that experimental water flumes do indeed produce "dunes that are downsized copies of desert dunes" (Kroy and Guo, 2004). At the root of the debate must lie a fundamental question of sediment transport mechanisms: the relative roles of suspension, saltation, and creep in subaqeuous vs aeolian environments, as well as the impact of the fluid and fluid flow properties (e.g.…”

How do bedform patterns arise? New views on the role of bedform interactions within a set of boundary conditions

“…One implication of bedform-pattern development at the interacting-bedforms level is that it justifi es the use, for example, of water ripples as a proxy to address pattern development in aeolian dune fi elds (Hersen, 2005). Morphological and dynamic differences obviously exist between different types of bedforms in differing fl uids (Endo et al, , 2005. In hierarchy theory, however, these differences exist at the bedformfl ow level.…”

Cellular model for sand dunes with saltation, avalanche and strong erosion: collisional simulation of barchans

“…It is an important issue to understand the differences between subaqueous dunes and aeolian ones. Some morphologic relationships known for aeolian barchans are applicable also to aqueous barchans when appropriately rescaled, depending on the materials and fluids (Hersen et al, 2002;Endo et al, 2005;Claudin and Andreotti, 2006). Furthermore, Endo et al (2005) have reported some differences in the shapes of barchans that are attributable to differences in the sediment transport mechanism.…”