Fick's law has been used to simulate gas systems within soil, although this law can be applied only to binary gas systems and the eŠect of the Knudsen diŠusion is not considered. By contrast, the dusty gas model can be applied to multi-component gas systems with Knudsen diŠusion. Blanc's law is a simpliˆed version of the dusty gas model, but it can be used only for gas systems in which the tracer gas is dilute. Although the dusty gas model is superior to other methods for simulating gas systems within soil, it is not generally used because of its complexity. Numerical techniques such as the Eulerian-Lagrangian method for solving the advection-dispersion equation can be used to simulate the migration of chemical substance in the water or gas phases of soil within the range of every P áeclet number. We derived the compound diŠusion coe‹cient and compound velocity from the dusty gas model and formulated the advectiondiŠusion equation with these values by using the characteristicˆnite element scheme. Results of the model developed here were consistent with the results of column experiments conducted in this study, and the precision of the developed model was veriˆed.
To simulate the dynamic interaction between a saline lagoon and a ground water system, a numerical model for two-dimensional, variable-density, saturated-unsaturated, and coupled flow and solute transport (saltwater intrusion by finite elements and characteristics [SIFEC]) was modified to allow the volume of water and mass of salt in the lagoon to vary with each time step. The modified SIFEC allows the stage of a lagoon to vary in accordance with a functional relation between the stage and water volume of the lagoon, and also allows the salt concentration of the lagoon to vary in accordance with the salt budget of the lagoon including chemical precipitation and dissolution of salt. The updated stage and salt concentration of the lagoon are in turn used as transient boundary conditions for the coupled flow and solute transport model. The utility of the modified model was demonstrated by applying it to the eastern Mediterranean coastal region of Turkey for assessing impacts of climate change on the subsurface environment under scenarios of sea level rise, increased evaporation, and decreased precipitation.
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