Experimental Study and Numerical Modeling of Surface/Subsurface Flow at Field Scale

Infiltration which occurred in the process of runoff on farmland surface causes the increasing of soil moisture in unsaturated zone. It’s necessary to comprehend the dynamic process during farmland runoff process, analyze the coupling mechanism of water movement and solute transport among surface/subsurface zone. In this paper, a physically-based, spatially-distributed model was built for simulation of surface/subsurface flow and the interactions between two domains. The system is represented by the three-dimensional saturated–unsaturated flow equation for the subsurface, coupled with the diffusion wave equation for overland flow, Ground surface unevenness at the grid scale is incorporated via the concept of detention storage. The system of equations is discretized using a fully implicit procedure, with the Newton-Raphson method to handle non-linearity of the equations. In order to assess this modeling approach, the simulations compared with the experiment results. It shows that the model can simulate the process of farmland runoff production and soil water movement accurately. Finally, Statistics and mass balance analysis was also performed to examine the model accuracy and response to changes of specific input data.