Initiation of motion of quartz sand grains

Authors: B B Willetts I K McEwan M A Rice

Publish Date: 1991

Volume: , Issue: , Pages: 123-134

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Abstract

Direct observation at a limited range of wind speeds of grain behaviour near the upwind edge of a sand deposit by means of highspeed film shows that disturbed grains usually but not always roll before taking off into reptation or saltation Timeaveraged description of the population of initial motions is deficient because of the importance of pronounced flurries of grain activity which occur at intervals The flurries are clearly associated with flow features in the clean air wind because they occur too close to the leading edge to be impact generatedAn adapted saltation model is used to explore the development of activity downwind which results from a sequence of first dislodgements into rolling or takeoff recorded on film The portrayal of the development of a saltation layer is plausible and can be checked by means of flux profile measurements However it emphasises the need for more information about turbulence in the grain laden layer

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