Problem with Fluid-flux BC (unsaturated model)

Hello everyone,

I have some troubles with my unsaturated model but I can not figure where is my mistake.

I'm modeling a simple 2D ground column (1*0.3 m) with only 2 boundary conditions : a fluid-flux BC on the top (very low, 1mm/y) and a hydraulic head below (0 m).
I correctly enter the different parameters for Van Genuchten's law and run it for 10 days.

[b]But when I look the Period budget it seems that my fluid-flux BC is not correctly met and to much water is entering on it. [/b]
The problem is really link to unsaturated because if I swicht to satured the same condition is fulfilled.

Have you an idea of what to do to be sure that my fluid-flux BC is correctly enter and met ?

Thanks a lot  ;)


Ps : I'm using FeFlow 7.0

Hi Paul,

The situation explained is a typical case. FEFLOW uses a backward calculation for the budgets. This means that you impose certain Fluid-Flux value and not necesarily you get the same in the budget panels. The budget calculation is based on the primary solution (heads). As you described, the case is very well observable in unsaturated models. From my experience this happens often when you add water into a very unsaturated profile. You can correct this mistmatch by improving the mesh discretization at the location of the boundary and/or using an analytical formulation for the capacity (Unsaturated Settings in the Problem Settings dialog).

Regards
Carlos

Hello Carlos,

Thank you it's clear and it's work, so perfect !  ;)

Thanks again and sorry for the late response

Paul