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Diffusion Approach for Suspended Sand Transport under Waves
Dang Huu Chung and Leo C. Van Rijn
Journal of Coastal Research
Vol. 19, No. 1 (Winter, 2003), pp. 1-11
Published by: Coastal Education & Research Foundation, Inc.
Stable URL: http://www.jstor.org/stable/4299143
Page Count: 11
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The results of theoretical studies on suspended sand transport over a rippled bed under irregular waves are presented. The mathematical model is based on the classical diffusion approach, in which both the turbulence-related diffusion and the effective wave-related diffusion are taken into account. Although the model is less effective in accurately simulating the instantaneous sand concentrations, the time-averaged sand concentration can be reasonably well simulated in the ripple regime using the calibrated equations. In particular, the proposed formula for the coefficient of diffusion by waves considerably improved the predicted value of the time-averaged vertical distribution of suspended sediment concentration. The accuracy of prediction for the suspended sediment transport is dependent on the type of applied bed-boundary condition for the sand concentration. The measured reference concentration should be used as the boundary condition at the reference level for fine sand. Steep vortex ripples for coarse sand and relatively flat ripples for fine sand occurred. For low ripple steepness and large wave height, the computed wave-related suspended transports for both types of boundary condition are directed onshore, in line with the measured results. The wave-related suspended transport increases with wave height and decreases with sand size. Suspended sediment transport mainly occurs in the near-bed layer, with a thickness of from 10 to 20 times the ripple height. The position of measurement should be as close to the bed as possible (down to z = 0.01 m above the bed) to determine accurate values of the depth-integrated transport rate.
Journal of Coastal Research © 2003 Coastal Education & Research Foundation, Inc.