Willy-willies in the Australian landscape: Sediment transport characteristics

Willy-willies (dust devils) are local convective circulations that characteristically arise in arid and semiarid environments. They are visually defined by their entrainment and transport of surface debris but little is known of their sediment transport role in the landscape. This study conducted in semiarid north-west New South Wales, Australia, provides quantitative information on the sediment entrainment and transport characteristics of willy-willies. The particles being transported in the lower 160 cm of 20 willy-willies were sampled using a tape-based vertical profile sampler developed as part of this study. The analysis of the samples, using a visual-based digital analysis method, revealed that almost 18% of the particles counted were being transported within 10 cm of the soil surface. It was also discovered that over 80% of the particles overall were 63 μm or smaller in major axis diameter. The results from this analysis, considered with respect to the characteristics of the surface the willy-willy traversed during sampling, show that the sediment load carried in the willy-willies increases with decreasing vegetation cover. This relationship with vegetation combined with the preferential entrainment of silt sized particles could, over time, make willy-willies a potent mechanism for the local differentiation of surface textures.