Question about GW discharge of a catchment with frozen ground.

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chen ding

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Jun 6, 2025, 2:37:24 AMJun 6

to Amanzi-ATS Users

Hi ATS users/developers,

I'm trying to simulate integrated hydrology of a small catchment covered with frozen ground.

And some questions occur with the subsurface water discharge at the catchment outlet.

I defined my catchment outlet followed the steps in https://groups.google.com/u/0/g/ats-users/c/uqqWTeZ8NyI .

The end point of the river was defined as the “outlet point”, with a length scale of 1000 (This value is large enough in my catchment). After extruded the mesh to 3D, the outlet covers more than 500 cells.

The vertical thickness of the model domain is 40 m, with the initial water table set 5 m below the surface. A constant head boundary of −25 m was assigned at the outlet to allow subsurface water to flow out of the catchment. However, the simulation results show that while subsurface water accumulates in the low-lying areas (which is consistent with expectations), it does not exit the catchment as anticipated.

Below are the distributions of liquid saturation and subsurface flow velocity for September.

Any comments would be appreciated.

Thanks

Chen Ding

Bo Gao

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Jun 6, 2025, 11:23:19 AMJun 6

to chen ding, Amanzi-ATS Users

Hi Chen,

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file? How did you define the flow out of the outlet in your observation? Did you collect surface flux or subsurface flux? Did you set "direction normalized flux" to true? What do you mean by "it does not exit the catchment as anticipated"?

Thanks,

Bo Gao

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chen ding

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Jun 6, 2025, 12:05:09 PMJun 6

to Amanzi-ATS Users

Hi Bo,

Thank you for your prompt response. I’ve marked my answers to your questions in blue.

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file?

No, this is a subsurface head boundary, the same as what I set in the previous 2D hillslope case.

I set this in the subsurface flow PK.

How did you define the flow out of the outlet in your observation?

Did you collect surface flux or subsurface flux? Yes

Did you set "direction normalized flux" to true? Yes

What do you mean by "it does not exit the catchment as anticipated"?

The BCs at the outlet is 25 m below the surface, then groundwater with a depth above 25 m should be able to flow out. However, the simulation results of liquid saturation and velocity show that very little water actually flows out. Additionally, the comparison between observed surface and subsurface flux also indicates that the amount of groundwater outflow is very limited.

Any comments would be appreciated.

Thanks

Chen Ding

Coon, Ethan

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Jun 9, 2025, 1:04:33 PMJun 9

to chen ding, Amanzi-ATS Users

All of that looks reasonable. I’m wondering what your temperatures are like in the saturated zone? You said it was similar to a 2D hillslope case – did you get the expected result in 2D?

Ethan

From: ats-...@googlegroups.com <ats-...@googlegroups.com> on behalf of chen ding <ding...@gmail.com>
Date: Friday, June 6, 2025 at 10:06 AM
To: Amanzi-ATS Users <ats-...@googlegroups.com>
Subject: [EXTERNAL] Re: Question about GW discharge of a catchment with frozen ground.

Hi Bo, Thank you for your prompt response. I’ve marked my answers to your questions in blue. I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file?

Hi Bo,

Thank you for your prompt response. I’ve marked my answers to your questions in blue.

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file?

No, this is a subsurface head boundary, the same as what I set in the previous 2D hillslope case.

I set this in the subsurface flow PK.

How did you define the flow out of the outlet in your observation?

Did you collect surface flux or subsurface flux? Yes

Did you set "direction normalized flux" to true? Yes

What do you mean by "it does not exit the catchment as anticipated"?

Any comments would be appreciated.

Thanks

Chen Ding

在2025年6月6日星期五 UTC+8 23:23:19<boga...@gmail.com> 写道：

Hi Chen,

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file? How did you define the flow out of the outlet in your observation? Did you collect surface flux or subsurface flux? Did you set "direction normalized flux" to true? What do you mean by "it does not exit the catchment as anticipated"?

Thanks,

Bo Gao

On Fri, Jun 6, 2025 at 2:37 AM chen ding <ding...@gmail.com> wrote:

Hi ATS users/developers,

I'm trying to simulate integrated hydrology of a small catchment covered with frozen ground.

And some questions occur with the subsurface water discharge at the catchment outlet.

I defined my catchment outlet followed the steps in https://groups.google.com/u/0/g/ats-users/c/uqqWTeZ8NyI .

The end point of the river was defined as the “outlet point”, with a length scale of 1000 (This value is large enough in my catchment). After extruded the mesh to 3D, the outlet covers more than 500 cells.

`

The vertical thickness of the model domain is 40 m, with the initial water table set 5 m below the surface. A constant head boundary of −25 m was assigned at the outlet to allow subsurface water to flow out of the catchment. However, the simulation results show that while subsurface water accumulates in the low-lying areas (which is consistent with expectations), it does not exit the catchment as anticipated.

Below are the distributions of liquid saturation and subsurface flow velocity for September.

Any comments would be appreciated.

Thanks

Chen Ding

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chen ding

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Jun 9, 2025, 10:43:51 PMJun 9

to Amanzi-ATS Users

Hi Ethan,

Thank you for your prompt response.

The temperature distribution shown below is from the same time (September) as the previous two figures.

A 2D simulation has previously been conducted on a localized cross-section of the catchment, but a full 2D simulation of the entire catchment has not yet been carried out.

Thanks

Chen

Coon, Ethan

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Jun 10, 2025, 10:01:05 AMJun 10

to chen ding, Amanzi-ATS Users

Hi Chen,

Mostly I’m asking if you have a 2D run (whether on a real or idealized hillslope) that implements the boundary condition you expect and gives the boundary outflows you expect.

If you’re not seeing the outflow from subsurface head boundary condition with a saturated zone on a 2D problem, I’ll have a much easier time helping you debug.

If the physics works in 2D, but not in your 3D domain, then the problem is probably your region definition.

Ethan

From: ats-...@googlegroups.com <ats-...@googlegroups.com> on behalf of chen ding <ding...@gmail.com>
Date: Monday, June 9, 2025 at 8:44 PM
To: Amanzi-ATS Users <ats-...@googlegroups.com>
Subject: Re: [EXTERNAL] Re: Question about GW discharge of a catchment with frozen ground.

Hi Ethan, Thank you for your prompt response. The temperature distribution shown below is from the same time (September) as the previous two figures. A 2D simulation has previously been conducted on a localized cross-section of the catchment,

Hi Ethan,

Thank you for your prompt response.

The temperature distribution shown below is from the same time (September) as the previous two figures.

A 2D simulation has previously been conducted on a localized cross-section of the catchment, but a full 2D simulation of the entire catchment has not yet been carried out.

Thanks

Chen

在2025年6月10日星期二 UTC+8 01:04:33<Coon, Ethan> 写道：

All of that looks reasonable. I’m wondering what your temperatures are like in the saturated zone? You said it was similar to a 2D hillslope case – did you get the expected result in 2D?

Ethan

From: ats-...@googlegroups.com <ats-...@googlegroups.com> on behalf of chen ding <ding...@gmail.com>
Date: Friday, June 6, 2025 at 10:06 AM
To: Amanzi-ATS Users <ats-...@googlegroups.com>
Subject: [EXTERNAL] Re: Question about GW discharge of a catchment with frozen ground.

Hi Bo, Thank you for your prompt response. I’ve marked my answers to your questions in blue. I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file?

Hi Bo,

Thank you for your prompt response. I’ve marked my answers to your questions in blue.

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file?

No, this is a subsurface head boundary, the same as what I set in the previous 2D hillslope case.

I set this in the subsurface flow PK.

How did you define the flow out of the outlet in your observation?

Did you collect surface flux or subsurface flux? Yes

Did you set "direction normalized flux" to true? Yes

What do you mean by "it does not exit the catchment as anticipated"?

The BCs at the outlet is 25 m below the surface, then groundwater with a depth above 25 m should be able to flow out. However, the simulation results of liquid saturation and velocity show that very little water actually flows out. Additionally, the comparison between observed surface and subsurface flux also indicates that the amount of groundwater outflow is very limited.

Any comments would be appreciated.

Thanks

Chen Ding

在2025年6月6日星期五 UTC+8 23:23:19<boga...@gmail.com> 写道：

Hi Chen,

I would guess the -25m constant head boundary condition is applied at the outlet at the surface domain, right? How did you define it in your input file? How did you define the flow out of the outlet in your observation? Did you collect surface flux or subsurface flux? Did you set "direction normalized flux" to true? What do you mean by "it does not exit the catchment as anticipated"?

Thanks,

Bo Gao

On Fri, Jun 6, 2025 at 2:37 AM chen ding <ding...@gmail.com> wrote:

Hi ATS users/developers,

I'm trying to simulate integrated hydrology of a small catchment covered with frozen ground.

And some questions occur with the subsurface water discharge at the catchment outlet.

I defined my catchment outlet followed the steps in https://groups.google.com/u/0/g/ats-users/c/uqqWTeZ8NyI .

The end point of the river was defined as the “outlet point”, with a length scale of 1000 (This value is large enough in my catchment). After extruded the mesh to 3D, the outlet covers more than 500 cells.

Error! Filename not specified.Error! Filename not specified.`

The vertical thickness of the model domain is 40 m, with the initial water table set 5 m below the surface. A constant head boundary of −25 m was assigned at the outlet to allow subsurface water to flow out of the catchment. However, the simulation results show that while subsurface water accumulates in the low-lying areas (which is consistent with expectations), it does not exit the catchment as anticipated.

Below are the distributions of liquid saturation and subsurface flow velocity for September.

Any comments would be appreciated.

Thanks

Chen Ding

Error! Filename not specified.Error! Filename not specified.

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To view this discussion visit https://groups.google.com/d/msgid/ats-users/0126261c-74e3-49d7-b8b2-ae4e19bc27e4n%40googlegroups.com.

chen ding

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Jun 11, 2025, 12:04:28 AMJun 11

to Amanzi-ATS Users

Hi Ethan,

Thank you for your prompt response. The physics does works in 2D, and I will doble check my mesh and region definition to try to solve this problem.

Best,

Chen

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