A Fully Coupled Numerical Simulation Of Water Movement And Solute Transport In Surface And Soil

The construction of numerical models for the transport of water and solutes in surface water and soil water is an important tool for studying the transport of water and solutes in surface water and soil water and for gaining a deeper understanding of the mechanisms and patterns of the hydrological cycle.In this paper,a fully coupled model of surface water-soil water movement and solute transport is constructed to simulate surface water movement,soil water movement and solute transport in this process.The model uses a two-dimensional diffusion wave equation to describe surface runoff movement;the traditional three-dimensional Richards equation is chosen to represent soil moisture movement,and the convective dispersion equation is used to describe solute transport in surface water and soil water.The dual node approach was chosen to couple the two water movement equations of surface and soil by Darcy’s law to construct a water movement model of surface water soil water.On this basis,the solute exchange between surface water and soil water is calculated based on Darcy’s flux and solute concentration to realise the coupling of solute transport in surface and soil,so as to construct a fully coupled numerical simulation of water movement and solute transport in surface and soil.In this paper,published field slope runoff test and indoor soil tank nitrogen migration test were selected for the calibration and verification of the model.By adjusting the model parameters through trial and error method and mathematical evaluation index,the optimal model parameters were obtained,and the model parameters were calibrated.Other test data were selected to verify the calibrated model.The comparison of measured data shows that the model can simulate the surface runoff movement and solute transport well.The parameter evaluation method was used to evaluate the parameters of the model constructed in this study,and the influence of different parameters on the simulation results was analyzed.The results showed that:(1)With the increase of Manning’s roughness coefficient,the production time of surface runoff is delayed,and the runoff volume gradually decreases.With the increase of Manning’s roughness coefficient,the influence of the model on surface runoff simulation is more pronounced.(2)The saturated hydraulic conductivity has a significant impact on the timing,velocity and steady flow rate of surface runoff production.Increasing the saturated hydraulic conductivity parameter leads to a decrease in the modelled value of surface runoff.The saturated hydraulic conductivity has a greater influence on the modelled results of surface runoff variability than does the Manning’s roughness coefficient.Surface runoff with larger pore size distribution indices exits earlier and the runoff rate increases more rapidly.The modelled surface runoff results decrease as the pore size distribution index increases during the later stable outflow phase of the simulation.When the pore size distribution index varied by the same magnitude as the saturation hydraulic conductivity,the pore size distribution index changed the calculated results less than the saturation hydraulic conductivity.The inlet suction inverse has a more significant effect on surface runoff than any other parameter.The higher the inlet suction inverse,the faster the surface flow production rate,while the steady flow rate increases with increasing inlet suction inverse.(3)As an important parameter for realising the coupling of soil water surface water and solute transport,the modelled surface runoff flow tends to increase gradually with increasing coupling length,i.e.the surface runoff flow is positively correlated with the coupling length parameter.However,under certain conditions,the sensitivity of the coupling length is not high compared to the surface and soil hydraulic parameters,reflecting the reasonableness and superiority of using this parameter to realise the model coupling.The newly constructed fully coupled model of surface water and soil water and solute transport will improve the understanding of surface and soil water and solute transport and has important application value for the prevention and control of agricultural non-point source pollution and water resources planning and management.