Catarina Diamantino

Dear Thierry,
For now I do not have convergence problems.
Some answers:
1) Initially yes, but I have made some changes. Now I have:
  Slice1 – free&movable
  Slice2 – unspecified
  Slice3 - unspecified
  Slice 4 – fixed
  Layer 1 – unconfined aquifer
  Layer 2 – impermeable layer
  Layer 3 – confined and unconfined aquifer
2) Both aquifers are discharging to a estuary zone not yet to the sea both. Saltwater edge is not considered.
3) I will have to put some pumping
4) Boundary conditions are:
North – Flux boundary (inflow)
East and west – impermeable
South - Head boundary (zero)
5) For now, still in steady sate.
Best regards,
Catarina

Just a small correction to my previous reply - layer3 is not always a confined aquifer, so slices2 and 3 should be unspecified (as you were saying).

If I consider the solution you refer in your last reply, then:
1) About my piezometric level, it is always in layer1, which is correct for a unconfined aquifer.
2) But for layer3 it is always above the top of the aquifer (elevations defined in 3D slice elevation) which is correct for a confined aquifer but not when this aquifer changes to unconfined.

Does this mean that I should only consider the piezometric level from layer1 in this area?
(values from all slices in this area are almost the same)
Best regards
Catarina

Dear Thierry
thank you for your suggestions.
The first model I have created was done as you said, just changing the hydraulic parameters in layer1. Then I would not have dry cells. Then the model calculates piezometric levels for layer1. Is it possible that this piezometric level is representing different aquifers in the same layer? I am not sure about this. That is why I have changed this approach.
Yes, you are right - layer2 is impermeable and not a confined aquifer. I have assigned it fixed because after a fixed slice there is always a confined aquifer, that is layer3.
Best regards.
Catarina

OK!!
Very simply is something like this:
Elevation of topography from 0 (coast line) to 50 m (hilly zone)
Piezometric level in unconfined aquifer - from 0 to 10 m above sea level
Piezometry level in confined aquifer - from 0 to 8 m above sea level.
I have reduced layer1 and layer2 thickness in the hilly zone (so their elevation is something like 49 m and 48 m, above sea level, in this area)
Best regards,
Catarina

Dear Thierry,
Thank for your comments.
You are correct in what you just said.
But still I have convergence problems.

The hydrogeological configuration is a plain area where I have a unconfined aquifer and a confined aquifer (separated by an impermeable layer) and a mountain area where my first aquifer disappears and I will just have the confined aquifer, that changes in this part to an unconfined aquifer.

In terms of layer geometry I suppose the best option is to reduce the thickness of layer1 and layer2 where they should not appear (in the hilly area). So, slice 2 and slice 3 elevations are quite high in this area, similar to the topography elevation. The piezoemtric head is always below those layer bottoms and I have convergence problems and dry cells.

Is there another way of creating this layer geometry in a way I will not have dry cells in the hilly zone?
If layers have to be continuous in the model domain how can I make then just disappear?
Some help is appreciated
Best regards
Catarina

Dear Thierry
Thank you for your answer.

Yes, you have understated correctly the layer geometry.

I have put free&movable at the top, fixed, phreatic and fixed for the following slices.

Yes, I have problems with dry cells and I used the option “natural constrain conditions” (residual water depth for dry elements) to make the model converges. But the results for piezometry, after model runs, are too high in the dry cells area (they are set equal to the bottom elevation of layer1). So, I have read in the “help menu about constrains” that this constrain is optional and can be set to inoperative, then the hydraulic head can fall below the aquifer bottom. The results improved a lot with this.

But can I say that I have an unsaturated condition in this part of layer1? How can I be sure?

If this is correct then I found what I was looking for because I would not want a piezometric distribution where I have no aquifer.

The piezometric distribution for the confined aquifer is given in slice3.
Can I assume this piezometry represents confined and unconfined conditions in the same slice?

Can I please have a comment on this issue?
Best regards
Catarina

I would like to put the following questions:

I am modeling two aquifers separated by an impermeable layer (layer2),
a unconfined top aquifer (layer1) and a confined aquifer (layer3) in the bottom.

The unconfined top aquifer does not fill all area of model domain because my bottom confined aquifer outcrops in a small area and passes from a confined to a unconfined aquifer.

What is the most appropriated option to model this situation: 1) layer1 representing two aquifers, by assigning the respective hydraulic properties from each aquifer to each aquifer area or, 2) to decrease the thickness of layer1 when the bottom aquifer is outcropping?

I am modeling slice1 as free and movable, slice2 as fixed, slice3 as phreatic and slice4 as fixed.

If I use the first option, what is representing the piezometric distribution of layer1 in that area of my model that concerns the bottom aquifer?

(I am using FEFLOW v5.0)
Some help is appreciated.
Catarina