Measurements of sand transport by wind on a natural beach |
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Authors: | J N SVASEK J H J TERWINDT |
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Institution: | Consultant Coastal Engineer, Schiekade 189, Rotterdam and Rijkswaterstaat-Deltadienst, van Alkemadelaan 400, The Hague, The Netherlands |
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Abstract: | Bagnold's (1954) and Kawamura's (1951) formulae may be used for the calculation of the sand movement on a natural beach, provided the shear stress velocity U* > 0·D4 m/s. Great discrepancies have been found between calculated and measured sand transport rates for U* < 0·D4 m/s, mainly because of the capillary forces acting on a wet beach. The measured critical shear velocity U*c at the beginning of sand movement on a clean dry beach agrees very well with that predicted by Bagnold's formula. On a dry beach where the sand grains are stuck together, U*c was found to be about 10% higher. On a wet beach U*c appeared to depend on the moisture content of the surface layer. Grain size is a determining parameter in the U*c-moisture content relation. When the angle a between the wind direction at sea and the dune face is between 15° and 85° the streamlines of the wind will bend in the vicinity of the dune face. In consequence this may influence the direction of sediment movement. |
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