Citation:

He, J., Mohamed M. Hantush, L. Kalin, M. Rezaeinzadeh, AND S. Isik. A two-layer numerical model of soil moisture dynamics: Model development. JOURNAL OF HYDROLOGY. Elsevier Science Ltd, New York, NY, 602:126797, (2021). https://doi.org/10.1016/j.jhydrol.2021.126797

Impact/Purpose:

Simulating water moisture flow in variably saturated soils with relatively shallow water table is challenging due to high non-linear behavior of Richards’ equation (RE). In this paper, a two-layer- approximation of RE was derived, which describes dynamics of vertically-averaged soil moisture content and flow in the root zone and the vadose zone below. To this end, the partial differential equation (PDE) describing RE was converted into two-coupled ordinary differential equations (ODEs) describing vertically-averaged soil moisture dynamics in the two soil zones subject to a deep or shallow water table and variable soil moisture flux and pressure conditions at the surface.

Description:

Simulating water moisture flow in variably saturated soils with a relatively shallow water table is challenging due to the high nonlinear behavior of Richards' equation (RE). A two-layer approximation of RE was derived in this paper, which describes vertically-averaged soil moisture content and flow dynamics in the root zone and the unsaturated soil below. To this end, the partial differential equation (PDE) describing RE was converted into two-coupled ordinary differential equations (ODEs) describing dynamic vertically-averaged soil moisture variations in the two soil zones subject to a deep or shallow water table in addition to variable soil moisture flux and pressure conditions at the surface. The coupled ODEs were solved numerically using the iterative Huen's method for a variety of flux and pressure-controlled top and bottom boundary conditions (BCs). The numerical model was evaluated for three typical soil textures with free-drainage and mixed flux-pressure head at the bottom boundary under various atmospheric conditions.

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