Water Content Post-processing

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K_Makara
Posts: 6
Joined: Thu Aug 05, 2021 6:12 pm
Location: Korea

Water Content Post-processing

Post by K_Makara » Sat Sep 18, 2021 6:43 pm

Dear all,

I have run Hydrus 1D for infiltration of water into the soil profile. I use pressure head boundary condition at the Upper Boundary Condition. The input time Variable Boundary Conditions is shown in the picture. After I run the calculations I see the wetting boundary in the Profile information of the Water Content are all becomes equal to the saturated water content. but if we see on the input data when the times equal 1 day to 4 days, 5 days the pressure head is equal to Zero opposite to the Water content that all the print times the wetting front becomes saturated all the print times? So what wrong with this problems? I have try so many way but it remain the same!
In my opinion, this water content should be become unsaturated when the input pressure head become to zero. Could you help me to solve this problems?

Thank in advance

Best Regards
K. Makara
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Jirka
Posts: 5317
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Water Content Post-processing

Post by Jirka » Sat Sep 18, 2021 8:38 pm

Quote “So what wrong with this problems?”
Problem seems to be your basic understanding of soil physics. A zero pressure head BC does not mean a zero flux BC, it means a zero pressure head at the boundary. Note that the zero pressure head corresponds to full saturation (see the retention curve).

If you want to alternate between pressure head and flux BCs, you need to use the “Variably Pressure Head/Flux” BC and tell the code when the head or flux (which can be specified to be zero) is to be considered. A Dirichlet (head) BC never (or rarely) leads to zero flux.

J.

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