Model a “subsurface dam” using the Horizontal Flow Barrier (HFB) package

[aziz]

Dear all,

I am trying to model a “subsurface dam” using the Horizontal Flow Barrier (HFB) package which simulates thin low-permeability geologic features to impede the horizontal flow of groundwater.

I have a model with two alluvium layers which are shown in the attached schematic figure.

In the HFB package, the cell boundary represents a vertical face between two adjacent cells. The question here is how I can define a barrier within one cell (layer) up to a specific level rather than the whole cell thickness (like layer 1 in the figure).

Your help and insight would be highly appreciated.

 

Best regards,

[Sean Czarniecki]

To simulate it exactly as you show it, you would have to split Layer 1 into 2 layers, so that the HFB goes up to the elevation you choose.  The other way to do it (without splitting layers) could be to allow flow through the HFB that is equivalent to the fraction of layer thickness that is open (the HFB is across the full thickness, but not totally impermeable).

[aziz]

Dear Sean,

Thanks for your reply.

I have a very sophisticated MODFLOW 6 model with Octree grid and I’ve calibrated and validated the model (attached figures).

If I want to split layer 1, the Ugrid will be regenerated again and I need to define again the materials and probably calibrate the model. How I can split layer 1 without regenerating the Ugrid?

 

Thanks,

[Sean Czarniecki]

An excellent question.  I don't know if the GMS tools will work to do this or not with the Ugrid (I haven't tried it in your situation).  In other cases, I would take a side view of the grid (general mode), select the layer with the layer select tool, right mouse button, redistribute from 1 to 2 layers. 

[aziz]

Dear Sean,

Thanks for your reply.

I’ve done your suggestion and the result was new UGrid.

When I select layer 1 and select right mouse button, there is no option to redistribute and there are Refine and Split layer options which I tried the Split layer option and the result was new UGrid (attached figure). For the new UGrid, I need to initiate the MODFLOW again and re-do all the work I have done before again.

I would appreciate it if you can give me a solution to split layer one without regeneration of UGrid.

 

Best regards,

[Sean Czarniecki]

Sorry that my suggestion hasn't worked out - I haven't used UGrid before, so I don't have an answer for you.

 

[aziz]

Thanks Sean,

You've done your best to resolve the problem.

I hope the GMS developers can help me to solve this issue.

 

Best regards,