MARUN numerical model and its applications in various coastal aquifer systems

Abstract:

The numerical model MARUN is able to simulate density-dependent variably-saturated flows in two-dimensional porous media. Since its development in 1999, it has been widely used in various coastal aquifers. We summarized the generalizations and improvements since 2008, focusing on the following aspects. (1) It was found that the method proposed by Yeh (1981, Water Resources Research, 1529-1534) for calculating the nodal Darcy velocity, which was used in the original MARUN, is suitable only for homogeneous aquifer. For the case of piecewise-constant hydraulic conductivity, nodal Darcy velocity obtained by the Yeh’s (1981) method may become unreliable, or even against common sense on nodes near the interface of two different porous media. We improved the method for calculating the nodal Darcy velocity for piecewise-homogeneous porous media so that the results are reliable in any case. (2) The fixed time-step used in the original version of MARUN is improved to be variable. It can be automatically increased or decreased accoridng to the convergent speed of the numerical Picard iteration for solving the nonlinear groundwater flow equation. If the numerical Picard iteration converges too quickly, the time step is increased, otherwise, decreased. (3) Tidal loading term is incorporated for groundwater flow overlain by tidal seawater, which has variable loading on the pore water beneath the seafloor. Examples with applications are given to shown these improvements.