Flow dynamics and sediment transport over a reversing barchan, Changli, China

The flow and sediment transport over a reversing ~ 6.9 m-high barchan dune is examined on the Changli Gold Coast in Hebei Province, China. Wind velocity profiles are non-logarithmic, exhibit rapid accelerations up slope, and display near-surface jets at the dune crest and downwind lee slope. From the windward lower slope to dune crest, the wind speed at 5 cm height increased by 55%. The windward slope is a slipface and therefore has a significantly greater gradient than most 'normal' windward slopes, and the magnitude of speed-up is significantly greater (speed-up ratio of 5.25). The majority of sediment was transported in the 0-4 cm height above the bed range. Maximum total sediment flux occurred at the dune crest and was greater than the total flux from three other sites combined. The leeward mid-slope sedimentation rate is strongly influenced by the sediment plume streaming upwards and downwind from the actively reversing dune crest. Dunes in the process of reversing display quite different wind flow and sedimentation patterns than when the dune is in 'normal' flow conditions.