A Comprehensive Quasi-3D Model for Regional-Scale Unsaturated-Saturated Water Flow

Abstract. For computationally efficient modeling of unsaturated-saturated flow systems of regional scale, it is necessary to use Quasi three-dimensional (3-D) schemes that consider one-dimensional (1-D) soil water flow and 3-D groundwater flow. However, it is still practically challenging for regional-scale problems due to the high non-linear and intensive input data needed for soil water modeling, the reliability of the coupling scheme, and the complicated modeling operation. This study developed a new Quasi-3D model coupled the soil water balance model UBMOD with MODFLOW. A new iterative scheme was developed, in which the vertical net recharge and unsaturated zone depth were used as the exchange information. A modeling framework was developed by Python script to wrap the coupled model, the pre- and the post-process modules, which gave a comprehensive modeling tool from data preparation to results displaying. The strength and weakness of the coupled model are evaluated by using two published studies. The comparison results show that the coupled model is satisfactory in terms of computational accuracy, mass balance error and cost. Additionally, the coupled model is used to evaluate groundwater recharge in a real-world study. The measured groundwater table and soil water content are used to calibrate the model parameters, and the groundwater recharge data from a two years’ tracer experiment is used to evaluate the recharge estimation. The field application further shows the practicability of the model. The developed model and the modeling framework provide a convenient and flexible tool for evaluating unsaturated-saturated flow system at the regional scale.