Unsteady Solute-Transport Simulation in Streamflow Using a Finite-Difference Model.

摘要

A computer program for simulating one-dimensional,unsteady solute transport in gradually varied streamflow has been developed and documented. Before using the solute-transport model, a flow model must be used to calculate and store necessary flow data at each cross section and each time step. Such a flow model is available and documented. Given the flow and solute-inflow data,the digital model will calculate a time-series of concentration values for any point in the stream. The conservative form of the mass-transport equation has been selected as the basis of the model. The solution of the equation is obtained with an implicit finite-difference method. The grid arrangement uses six nodal points and calculates the spatial and temporal derivatives at a slightly off-centered point. The off-centering is a compromise between numerical dispersion and accuracy. A tridiagonal matrix is created and solved at each time step by the Thomas algorithm. The solute-transport model allows the solute to enter the stream at an unsteady rate from the upstream boundary and tributaries. A steady inflow of solute can enter the stream with lateral seepage. An unsteady solute flux,uniform over the reach,from a source or sink can be taken into account. The solute concentration can decay by using a constant decay coefficient.