Interactions between airflow and valley topography with implications for aeolian sediment transport

The local topography of a landscape can have a profound influence on airflow characteristics and cause modifications to broader synoptic scale winds. This paper reports the results of a preliminary field study examining the effects of a valley on wind velocity and direction. Anemometers and wind vanes were used to measure airflow characteristics upwind, within and downwind of a 20 m deep and 175 m wide dry valley in the central Namib desert. The field data indicate an upwind region of flow acceleration, a minimum in flow velocity in the center of the valley, flow acceleration toward a maximum at the downwind valley edge and subsequent deceleration toward starting velocities downwind of this edge. The development of a flow separation region at the leading edge of the valley and the range of flow distortion are affected by the incident angle of the approaching wind to the axis of the valley. A conceptual model indicating the potential implications of these findings for aeolian sediment transport processes in the vicinity of dryland valleys is presented.