Search

Presents a corrected reprint of the article "Influence of Turbulence on Bed Load Sediment Transport’ ” by B. Mutlu Sumer, Lloyd H. C. Chua, N.-S. Cheng, and Jorgen Fedsoe," published in the January 2005, Volume 131 of the "Journal of Hydraulic Engineering".

The paper investigates the influence of the resistance coefficient variability onto the spatial development of roll-waves. Two models, based on time-asymptotic solutions of the linearized St. Venant equations, subject to either impulsive or oscillating perturbation, have been modified by including the dependence of the resistance coefficient on flow conditions, wall roughness, and fluid viscosity. Independently of the perturbation type, it has been shown that the hypothesis of constant resistance coefficient leads to underestimate the disturbance spatial growth. Theoretical predictions are finally compared with results of a fully nonlinear model and with literature experimental data for several combinations of Froude and Reynolds numbers and relative roughness values. The representation of variability of the resistance coefficient fundamentally improves the performance of minimum channel length criteria, whereas its neglect may lead to noncautious channel design. [ABSTRACT FROM AUTHOR]

The authors comment on the article "Analysis of Dynamic Wave Model for Unsteady Flow in an Open Channel" by Maurizio Venutelli. They mentions the analytical expressions of phase and group speeds and wave amplitude that have been derived by studying the linearized shallow-water equations (SWEs). The author states that the result of the study allows assessing convergence and accuracy of numerical schemes commonly.

Fast geomorphic transients may involve complex cenarios of sediment transport, occurring near the bottom as bed load (i.e., saltating, sliding, and rolling) or as suspended load in the upper portion of the flow. The two sediment transport modalities may even coexist or alternate each other during the same event, especially when the shear stress varies considerably. Modeling these processes is therefore a challenging task, for which the usual representation of the flow as a mixture may result in being unsatisfactory. In the present paper, a new two-phase depth-averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads. Distinct phase velocities are considered for bed load, whereas the slip velocity between the two phases is neglected in the suspended load. It is shown that the resulting two-phase model is hyperbolic, and the analytical expression of the eigenvalues is provided. The entrainment/ deposition of sediment between the bottom and the bed load layer is based on a modified van Rijn transport parameter, whereas for the suspended sediment a first-order exchange law is considered. A numerical finite-volume method is used for the simulation of three dam break experiments found in the literature, which are effectively reproduced in terms of both free surface elevation and bottom deformation, confirming the key role played by the solid concentration variability even for two-phase models. [ABSTRACT FROM AUTHOR]