I would like to add to this post (if I may). I understand that layers below fixed slices remain saturated, but after running a model that has a moveable surface above a series of fixed slices, with boundary conditions assigned to lower layers (eg wells, or similar) that should desaturate shallower layers, the simulated pressures can be negative (i.e. unsaturated). Is this because pressure is simple calculated after the simulation (Head = elevation + pressure head, rearranged of course)? Does this also mean that with a fixed slice, although a simulated head may be below a layer base elevation, Feflow (in simple terms) uses the Transmissivity based on the assigned aquifer thickness and hydraulic conductivity, the specific storage (ignores storativity) and the gradient (regardless of whether the actual elevations are above or below the assigned slice elevations) to simulate the overall result? And as a result there will always be flow, even when simulated heads are below the based on the assigned slice elevation (when assigned as fixed).
