Hello,
I am currently using Hydrus-1D to design a capilary barrier with a fine grain layer over a coarser grain layer to look at the effects of different soil types on the capillary barrier. Currently for clay over sand when using the lower boundary conditions of free drainage (which I would think is the sensible option to use as a coarser lower layer in a capilary barrier is unlikely to support much suction when a wetting front arrives) it gives me the error the numerical solution has not converged. However if I use the seepage face with h=0 option the calculations are completed normally, I am unsure as to why the free drainage option gives me an error?