Variable boundary head at variable boundary fluxes

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Iliketrains
Posts: 4
Joined: Fri Apr 30, 2021 6:38 am
Location: Germany

Variable boundary head at variable boundary fluxes

Post by Iliketrains » Fri Apr 30, 2021 7:48 am

Hello,
I am currently simulating a Hyprop experiment with Hydrus 2D/3D. I entered a look-up table with experiment data and chose a variable boundary flux at the bottom. All other sides have no flux. I entered the evaporation rates from the experiment. Everything works fine, besides the fact, that the variable boundary head 1 is showing an up and down in the figure. I think, that this is not right. Why is it like that and can I change it?
Thanks in advance for your answers!
I hope you can open my file.

And I have another question concerning the actual evaporation rate when applying the atmospheric boundary. When does it get 0?
Attachments
Hyprop.zip
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Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Variable boundary head at variable boundary fluxes

Post by Jirka » Fri Apr 30, 2021 8:02 pm

The results are exactly as I would expect them to be for the conditions you specified. Note that the surface pressure head starts increasing at the time when you keep the evaporation flux constant (after its dramatic decrease), i.e., the soil can bring moisture to the surface faster than it evaporates. This would not happen if you have a gradual decrease of the evaporation flux.

The evaporation flux will go down to zero once the soil is unable to bring the moisture towards the surface (see the first, second, and third stage of evaporation in Soil Physics or hydrology books). For the code to be able to accommodate it, you need to use either the Atmospheric BC or you need to request in BC options to treat a Time-Variable Flux BC as an Atmospheric BC.

J.

Iliketrains
Posts: 4
Joined: Fri Apr 30, 2021 6:38 am
Location: Germany

Re: Variable boundary head at variable boundary fluxes

Post by Iliketrains » Mon May 03, 2021 10:20 am

Thank you very much for your reply!! It worked when I put in more gradual evaporation rates.
I have now the problem, that when I apply the atmospheric boundary at the top, the pressure heads are similar to the one in the experiment, but the water contents are to high. When I apply the variable flux boundary my water content is perfect, but the pressure head is way to high.
So I would need a function, that I can enter the evaporation flux and also limit the pressure head at the top. Is this possible ?
Thanks in advance for your reply!

Jirka
Posts: 5268
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Variable boundary head at variable boundary fluxes

Post by Jirka » Mon May 03, 2021 7:35 pm

Did you read the last sentence of my answer? J.

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