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Eulerian equations for the vertical flux and momentum of suspended particles in dilute sediment-laden open-channel flow in equilibrium have been derived using the two-fluid approach. Reynolds averaging has been applied in order to allow validation of individual terms with experimental data. Consideration of the various terms of the vertical momentum balance with experimental flume data indicates that the drag force has to be separated into a mean and a turbulent contribution with different timescales, respectively, the (gravitational) particle timescale and the integral turbulence timescale. The resulting formulation further provides a new theoretical closure for the turbulent Schmidt number. DOI: 10.1061/(ASCE)0733-9429(2008) 134:9(1225) CE Database subject headings: Suspended sediments; Open channel flow; Turbulence; Two-phase flow.

The equation derived by Yigong Li and Ashish J. Mehta for determining the hindered settling speed of flocs in mudlike sediment suspensions and the three sets of experimental data they used to validate the equation are problematic. One problem with the equation is the discrepancies that result when it is applied to rigid noncohesive particles. One problem with their validation procedure is that model parameters were determined first by least-squares fitting of the same experimental data.