Coupling saturated and unsaturated flow: comparing the iterative and the non-iterative approach

Abstract

Abstract. Fully integrated three dimensional (3D) physically based hydrologic models usually require many computational resources. For many applications, simplified models can be a cost effective alternative. 3D models of subsurface flow are often simplified by coupling a 2D groundwater model with multiple 1D models for the unsaturated zone. The crucial part of such models is the coupling between the two model compartments. In this work we compare two approaches for the coupling. One is iterative and the 1D unsaturated zone models go down to the impervious bottom of the aquifer and the other one is non-iterative and uses a moving lower boundary for the unsaturated zone. In this context we also propose a new way of treating the specific yield, which plays a crucial role in linking the unsaturated and the groundwater model. Both models are applied to three test cases with increasing complexity and analyzed in terms of accuracy and speed compared to fully integrated model runs. The non-iterative approach is faster while the iterative approach is more accurate and robust. Besides, for the iterative coupling method a calibration of the specific yield is not needed.

Richards Equation at the Hillslope Scale: Can We Resolve the Heterogeneity of Soil Hydraulic Material Properties?

“…Additionally, macropore flow may occur at the bottom boundary of the hillslopes. This may make it necessary to separate material properties for the unsaturated and saturated dynamics, which can be accomplished, for example, through further simplifying the model by coupling the one‐dimensional Richards equation for the vertical dynamics and Boussinesq equation for flow in the saturated zone (e.g., Brandhorst et al., 2021; Hazenberg et al., 2015, 2016).…”