The non-linearity of unsaturated flow requests small time step and fine grid in the corresponding simulation,and the simulation often suffers from some unfavorable boundary conditions.Therefore,it is time-consuming to simulate the regional unsaturated-saturated flow by traditional numerical methods.In view of this issue,a 1D unsaturated model based on improved integrated Richards’equation coupled with 3D saturated flow model was proposed for the simulation of regional groundwater flow.The soil moisture was taken as primary variable in vadose zone. By separating the effect on soil moisture variation from pressure head and soil parameters, an improved integrated Richards’ equation model was presented to calculate the unsaturated flow in heterogeneous soil.A 3D groundwater model was established with control volume finite element method.These two models were coupled by their mutual nodes.The comparisons between results from the proposed model and Hydrus showed good agreement. Moreover, the proposed model takes the advantage of integrated Richards’ equation,thus it is more efficient to simulate large-scale flow problem with atmospheric boundary.
