I’ve been interested in shallow unconfined aquifer systems recently, so needed to account for water table conditions. Standard finite-element models (including FEST until now) generally represent saturated conditions within their elements. They then need to solve the difficult variably saturated equations to find the water table position… this can be hard and non-linear. We decided instead to adopt a variable transmissivity representation for the elements within which the water table fluctuates (similar to MODFLOW) by Incorporating Variable-shape Elements as a form of moving grid approach – FEST-IVE (Happy new Year!). Here is confirmation of its accuracy for a coarse grid model of the one-dimensional unconfined flow to a fixed head compared with the analytical solution using the Dupuit-Forcheimer approximation (neglecting vertical gradients gives a small error near the discharge).
