The curves for graded sands or gravels are constructed by proportional summation of the curves of the different fractions determined with the model for uniform sands and gravels after adjusting the liquid density and viscosity based on the fraction of fines.
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Miedema, S.A., "The Delft Head Loss & Limit Deposit Velocity Model". www.dredgingengineering.com. Delft, The Netherlands, 2012-now.