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Assessment of a 3D Variably Saturated Subsurface Model

Author(s): Daniel Caviedes-Voullieme; Javier Murillo; Pilar Garcia-Navarro

Linked Author(s): Pilar García-Navarro

Keywords: 3D Richards equation; Finite Volume; Mesh topology; Unsteady flow in porous medi

Abstract: Some environmental, irrigation and engineering applications have a special interest in the accurate simulation of 3D subsurface flows. The Richards equation is the physical model most used for single-phase, isothermal, variably saturated flow. It is a non-linear partial differential equation requiring numerical solutions which can be computationally expensive, specially in 3D domains where a large number of cells is necessary. In this work, a numerical model for the solution of the 3D Richards equation is presented. The scheme is built within the Finite Volumes framework and integrated implicitly in time. The implicit scheme is unconditionally stable in theory, though accuracy can suffer with large time steps. The model handles naturally dry or flooded conditions at the surface, as well as saturated or unsaturated conditions in the soil. The numerical scheme is shown to be mass conservative and accurate. It also degenerates easily into 2D and 1D models. Benchmarking is performed against 1D and 3D groundwater analytical solutions as well as experimental cases and synthetic test cases. By means of these tests the accuracy of the model is tested and efficiency is studied. Sensitivity to mesh resolution and structure is studied using hexahedral and tetrahedral cells. Sensitivity to time step size is also studied. Finally, the computational cost of the model is evaluated and the efficiency of different modeling choices is assessed.


Year: 2013

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