Question about surface–subsurface boundary conditions in ATS

[Felipe Silva Monsalves]

  Hello all,

 I am trying to simulate the flows within a soil cover over a saline waste pile (as shown in the image). To do this, I have used the integrated hydrology example. The results are not what I expected, and I am mainly wondering whether there is a conflict between the surface boundary conditions (critical depth) and the subsurface boundary conditions (seepage face pressure, to allow water to flow outward through the drains), since both boundary conditions are located in the surface layer. Is this possible to do in ATS? Would any of you have an idea or perhaps a recommendation on how to approach this? Additionally, since the surface has different breaks in slope, could this also create a problem that needs to be considered in some state or somewhere else?  

Thank you very much in advance.

Felipe

[Painter, Scott]

Hi Felipe, 

I don’t understand your configuration. Are the drains in the subsurface or on the surface? If it’s the latter, then how are they different from the rest of the surface?  What is the purpose of the drains? What are the yellow bars? 

If you’re using the integrated surface/subsurface configuration, I don’t think you need the subsurface BC. But  you may be able to use subsurface only depending on what you’re trying to do. In that case, you would want seepage face BCs on the side. 

Why is it not behaving as you expect? 

Scott 

From: ats-...@googlegroups.com <ats-...@googlegroups.com> on behalf of Felipe Silva Monsalves <felipe.sil...@gmail.com>
Date: Friday, December 12, 2025 at 7:49 AM
To: Amanzi-ATS Users <ats-...@googlegroups.com>
Subject: [EXTERNAL] Question about surface–subsurface boundary conditions in ATS

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[Felipe Silva Monsalves]

  Hi Scott,
Thank you very much for your response, and I apologize for only replying today. I was away for personal reasons, but I am now back at work.

  

As shown in the image, above the potash pile there are different soil layers. As indicated in blue, between the layers there is a drainage layer (gravel) to allow water to flow outward at each berm. Therefore, the drains are in the subsurface but discharge to the outside through the surface.

I am using the surface/subsurface configuration (later I would like to use priestley_taylor_canopy_evapotranspiration_relperm_trf.xml to account for different types of vegetation).

The general idea is to obtain the global water balance. To do this, I need to quantify the water that runs off on the surface, the water that leaves the system through the drains, the water that infiltrates into the potash pile, and finally the water that infiltrates at the bottom of the model toward the aquifer.

On the surface (lower right corner) I apply a zero‐gradient boundary condition, and at each drain outlet a seepage face pressure boundary condition. This is where my questions and doubts arise.

The drain outlets are located in the Surface layer. Is it possible to apply this? Can ATS handle this? The results I obtain show that water can only drain out through the last drain at the lowest part; the upper drains do not discharge water. In addition, the covers dry out too much, which causes the solution not to converge.

I would greatly appreciate any guidance and/or suggestions.
Thank you very much.

Felipe