Efficient and robust numerical modeling of variably saturated flow in layered porous media

We extend our recent work on higher-order time integration of Richards' equation to layered heterogeneous porous media, using a differential-algebraic-equation-based method of lines (DAE/MOL) approach. We show that the DAE/MOL approach is robust and efficient compared to standard low-order time integration methods for heterogeneous media. We also show the advantage of using an integral representation of permeability compared to a standard arithmetic mean for the test problems considered herein.