Software for evaluating sediment-induced stratification in open-channel flows

Open channel flow containing sediment suspension subjects itself to a density gradient in the vertical direction, i.e. density self-stratification, due to the tendency for suspended sediment to settle. Velocity and concentration profiles under the effect of density stratification may differ significantly from the conventional logarithmic and Rousean distributions associated with open channel flow. It is hence important to include this effect into flow computations in order to accurately predict flow characteristics such as the resistance coefficient, near-bed sediment concentration, flow and sediment discharge. In this study we introduce a software, StratSedOC, for such purpose. The application contains a user-friendly interface which allows users to evaluate and visualize the differences in the velocity, concentration and eddy viscosity profiles when stratification effects are taken into account. In addition to the standard logarithmic/Rousean formulation, the model uses three turbulence closures, i.e. an algebraic model (Smith–McLean) and two differential models (k-ε and Mellor–Yamada). The software application can also be used to study the effect of sediment mixtures on flow stratification under different boundary conditions for near-bed sediment concentration. Comparison among the model and experimental results suggests that the Mellor–Yamada model predicts a damping effect on the eddy viscosity which is similar to the Smith–McLean model, while the k-ε model consistently predicts weaker stratification effects. Based on this result, a modified boundary condition for the k-ε model is then proposed.