• ### Buondary and initial conditions

I have a sandstone block 24x19x16cm3. I know all the material properties of this block, since we have it in our labs.
the block is sealed on the side walls, while top and bottom faces are free to drain water.
In the lab test we put 5cm of water on the top of the block. After a while water started to flow out from the bottom. In 11 hour, with a linear law, the level of water on the top of the block become 2.5cm.
I need to set the bottom layer 'open', I mean that I need to let the water flowing out from the system without any constrains. Moreover I want to set as initial condition the hydraulic head = 5cm (ie initial ponding = 5cm) and see the evolution of the system so that I will be able to verify the time needed to the total infiltration.
I'm working with richard's equation, transient, 3D, initial moisture content=0.30, unsaturated flow porosity=0.45, Ks=5.5e-03cm/s, S_s=1, S_r=0.05, Vanghenuchten with a=0.071, n=1.7541.
I've tried to use 1st and 3th kind Boundary Conditions, but the rate budget is far from the expected values found in lab.