Investigating Turbulence-Driven Sediment Transport with Field Applications of Particle Image Velocimetry

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Our current capabilities for predicting amounts of sand moved by wind over beaches and in deserts perform poorly when tested in the natural environment. Accurate predictions are crucial, however, to many practical problems in resource management and environmental engineering, such as beach deflation, coastal dune and habitat development, soil erosion, and dust emissions into the atmosphere. The principal limitation of the current models is that they calculate transport rate only as a function of a single time-averaged wind speed. We know, however, that wind-blown sand - even over uniform beaches and desert surfaces - displays intricate and shifting spatial patterns, most visibly in the form of streamers or so-called 'sand-snakes'. Previous research has suggested that these patterns are formed by individual gusts, or eddies, of wind that generate and drive the streamers over the surface.The research project will determine the precise functional relationships between eddies in natural winds and resultant sand transport over the surface, with the goal of establishing a new quantitative and predictive model that explicitly incorporates parameters related to the turbulence.We do this by applying state-of-the-art video imaging technology in field experiments on a beach. The International Partner is deploying a laboratory-grade measurement system for tracking eddies in the wind as well as airborne sand grains through a powerful laser beam, filmed by multiple high-speed video cameras from different viewing angles. The PI will add to this his technique of filming streamers with ordinary GoPro sports cameras and analysing the footage to measure the movements and grain densities of these patterns as they approach and enter the laser beam. The combination of these two types of Particle Image Velocimetry on different spatial scales allows us to interrogate the precise links between wind turbulence and sand movement so that we can establish a mathematical model.