Transient Water Flow and Nitrate Movement Simulation in Partially Saturated Zone

Abstract

Water flow through vadose zone is important for soil ecology and for groundwater development. A thorough knowledge of water flow and solute transport through unsaturated zone is also needed for sustainable irrigation management, soil-water conservation measures, pollution risk assessment, groundwater recharge, and for applying remediation techniques. Therefore, in this study, practical and simulation experiments were performed to evaluate the role of drainage flux, recharge influx on moisture flow, and nitrate movement in subsurface. The water flow in unsaturated zone was simulated using the nonlinear Richards’ equation having dependency of its parameters on soil moisture content and pressure head. In this study, the following cases were evaluated for soil moisture and nitrate transport though variably saturated zones: (1) drainage flux to study domains, (2) recharge flux to study domains, (3) transient infiltration in unsaturated soil columns, and (4) nitrate movement in a two-dimensional (2D) sand tank setup. The single porosity model was used for the simulation of soil hydraulic parameters in the study domain. The results showed that the groundwater table position decreased with time quite significantly by applying drainage flux at the bottom boundary. The water table position in the study domain increased slowly under the constant recharge flux. The soil moisture front moved toward the groundwater level, when a constant infiltration flux was applied. Further, the nitrate movement was dominated by advective flux and significantly affected by the recharge flux in the vertical direction.