Numerical modeling of water flow below dry salt lakes: Effect of capillarity and viscosity

We investigate numerically the effects of capillarity and viscosity on density-dependent flows below dry salt lakes. The numerical model, MARUN (Boufadel, M.C., Suidan, M.T., Venosa, A.D., 1999a. A numerical model for density-and-viscosity-dependent flows in two-dimensional variably-saturated media. J. Contain. Hydrol. 37, 1-20) is used to assess the combined and separate effects of capillarity and concentration-engendered viscosity on the groundwater dynamics of a two-dimensional system simulating a dry lake. We found that accounting for concentration-engendered viscosity effects under saturated water flow conditions gives totally different groundwater dynamics from the case where these effects are neglected. However, concentration-dependent viscosity effects were minor when unsaturated water flow conditions were present. Under variably-saturated flow conditions, capillarity effects gave totally different hydraulics in the porous domain from the saturated flow case; upwelling regions observed under saturated flow conditions were downwelling when capillarity effects were present. A mesh orientation study revealed that density-dependent flows were susceptible to the orientation of the diagonals of the triangular elements. A discussion on the accuracy and the efficiency of the MARUN model in the context of density- and viscosity-dependent flows in two-dimensional variably-saturated media is also provided.