Residual water depth

Hi all!
i'm running a model with a single phreatic/confined layer.
-when i'm using "unconstained" for dring cells, my water budget is OK.
-when i'm using "constrained" to prevent cell drying and a "residual water depth"
  the outflow is much higher that inflow.

is that mean that FEFLOW solve the residual watertable issue by entering additional water to the dring cells?

if it so, i understand that i need to 1) not use the constarin option. 2) lower the conductivity on the area that is subject to drying.

is there another way to overcome this problem?
 

Hi Elad,

indeed FEFLOW adds water to the drying elements in case of 'unconstrained'. This is done by internally setting 1st kind boundary conditions at the corresponding nodes with h = z_bottom + residual water depth. You can analyze these boundary fluxes in the budget analyzer by using the buttons in the line in white characters at the bottom of the budget analyzer window.

The only possibility to avoid these additional injections of water is to use 'unconstrained'. The transmissivity for the dry areas is then calculated by residual water depth * conductivity. So using a low residual water depth, you might not have to lower the conductivity at all.

Cheers,
Peter

Gday Elad,

I was wondering how you faired with these changes. Specifically, what constitutes a "low" residual saturation depth? I am experiencing similar water budget issues with unconstrained setting and have applied a depth of 0.1m for residual depth. Is this an adequate number (in the ballpark) or should I be up-scaling  this value significantly? 

cheers mate
tim