Modeling non-cohesive suspended sediment transport in stream channels using an ensemble-averaged conservation equation.

摘要

Sediment transport modeling is important in the engineering and management of the river environment. In this study the transport of non-cohesive suspended sediment in erodible channels is considered. Lateral inflows and deposition and entrainment of sediment are incorporated in the formulation. Due to uncertainties in the parameters, the governing conservation equation is recognized as a stochastic partial differential equation, and a deterministic (ensemble-averaged) equation is developed and used. Variables in this one-dimensional equation are represented as averaged quantities, and their covariances are also taken into account.; Numerical solution of this equation allows the prediction of the space-time evolution of mean sediment concentration in the channel. A hypothetical test problem is constructed to examine the model behavior. Manning's coefficient, bed slope and bottom width are taken as the primary random parameters.; Results from solutions of the ensemble-averaged equation are compared with results from Monte Carlo simulations, which employ randomly generated parameters in the solution of the governing equations. The average values of variables and their covariances, which are needed in the solution of the deterministic ensemble-averaged transport equation, are also estimated from the Monte Carlo simulations. For comparison purposes, predicted values are also obtained by solving the deterministic transport equation without the covariance terms.; It is found that predictions obtained from the deterministic transport equation without the covariance terms deviate significantly from Monte Carlo simulation results, indicating that the former approach is not suitable. On the other hand, the ensemble averaged predictions compare favorably with the Monte Carlo simulation results except for certain intervals of the simulation time period. Even for those intervals the ensemble-averaged predictions are, in general, closer to the Monte Carlo simulation results than are the predictions from the deterministic transport equation without the covariance terms.; Results obtained in this study show the ensemble-averaging technique to be very promising in dealing with the complicated nature of fluvial hydraulics. Although Monte Carlo simulation is still required to obtain the various average, variance and covariance terms, which appear as parameters in the ensemble-averaged transport equation, the overall amount of computation is greatly reduced by using this equation.