3D model - Vadose zone well

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kkwak
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Joined: Fri May 17, 2019 12:02 am
Location: USA

3D model - Vadose zone well

Post by kkwak » Fri May 17, 2019 5:24 pm

To whom it may concern,

I'm developing a 3d model to simulate vadose zone well where the water is injected into the vadose zone (above groundwater table). This model consists of 3 layers of soil; clay, sand and gravel (both have Ks as 200 m/day and Qr as 0.176 and Qs 0.35).

The vadose zone well is only screened over very top part of the sandy layer (depth of 9.76m to 12.20m), and I'm using constant flow BC of 140 m/days for the flux into the domain. Also, groundwater table is at the depth of 14.6m.

I thought this should be relatively simple model, but I'm still getting wrong results (e.g. water content; the vadose zone gets filled up right after 0 days. I also used nodal recharge instead of constant flow BC but I'm getting same thing.

For your information, attached is my model file. If attached file is not working, please let me know I'll email another .zip file to you. It would be much appreciated if you can help me with this problem. Thank you.

Won
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Jirka
Posts: 4759
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: 3D model - Vadose zone well

Post by Jirka » Fri May 17, 2019 10:03 pm

You likely do not have sufficiently fine discretization around the well and thus the numerical solution does not converge. Note that variably-saturated flow (the Richards equation) requires much finer spatial discretization than saturated flow (the Bousinesque equation). Please see “rules about spatial and temporal discretization (FAQ: http://www.pc-progress.com/Documents/No ... zation.pdf. J.

kkwak
Posts: 3
Joined: Fri May 17, 2019 12:02 am
Location: USA

Re: 3D model - Vadose zone well

Post by kkwak » Sun May 19, 2019 12:45 am

Hi Dr. Simunek,


Thank you for your kind reply.

I made the mesh finer, but now I'm getting ORTHOMIN TERMINATES errors. After researching about it, I found that you have suggested using a smaller time step or setting a outflow boundary to solve the problem.

I tried to use 1e-6 days for initial time step and 1e-7days for minimum time step, and also I set new outflow variable head boundary with total head of -14.6 (groundwater table depth). However, I'm still getting same error.


Won

Jirka
Posts: 4759
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: 3D model - Vadose zone well

Post by Jirka » Tue May 28, 2019 12:52 am

Note that HYDRUS does not use total heads. It uses pressure heads, which are either negative in the unsaturated zone (capillary forces) or positive in the saturated zone (hydrostatic pressure). Gravitational heads are then considered automatically by the code, when there is the z-coordinate in the definition of the transport domain. The pressure head thus should be positive on the boundary that is below the water table. J.

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