• Unsaturated flow - Hysteresis effect


    I'm working on a sand column, which is unsaturated (partially saturated) and I want to simulate infiltration in the column in order to fit observed data.
    The observed data show a strong hysteresis effect.

    To do so, I have asked Feflow to consider hysteresis effect in the Problem settings and defined:
    - the Van Genuchten parameters for the main drying curve and the main wetting curve
    - the saturation limits for the main drying and wetting curve
    - initial conditions, close to residual saturation

    After injecting water at the top of the column (fluid flux), the water front mirgates well in the column and is welle drained at the bottom (fluid flux gradient).

    No oscillations problems or other problem, as I limited the time steps and refined the mesh.

    The problem is the following :
    when I plot at observation points the curve "pressure = f(soil moisture)" or "pressure = f(saturation)", the curve stricly follows the wetting curve, even after the water front has passed, where I would have think that the curve would switch to a drying scanning curve ...
    In fact, the hystérésis effect seems to be not considered ... and I don't uderstand why.

    Another question is the threshold mentionned in the Problem setting. By default, it is 0,01 m. When I change it (1e6 m in order to switch from wetting to drying theoretically faster), it doesn't change.

    Finally, how Feflow understand that the initial conditions correspond to drying or wetting conditions ?

    Thank you for your help.
  • Re: Vertical unsaturated colomn - Bottom BC

    Thank you for your answer !
  • Re: Inflowing Water to a Richards Eq. System

    Hi Bjorn,

    You said the inflow is computed by multiplying the flux by the length and a depth of 1 meter. How does it work when we are working on an axisymetric model : how is the inflow calculated ?

    Thank you
  • Vertical unsaturated colomn - Bottom BC


    I am working on a sand aquifer. The groundwater level is 50 m below the surface and I just want to simulate the first meters of the unsaturated zone. As the groundwater level is far below the unsaturated zone that I try to model, I don't know what kinf of bottom BC I can put : normally, I would have put a free drainage BC but it does'nt seem to exist on Feflow ...

    Can you please help me ?
    Best regards