cBot input method(EC simulation)

A discussion forum for Hydrus-1D users.
Post Reply
kiriru
Posts: 7
Joined: Fri Dec 13, 2019 4:42 pm
Location: Japan

cBot input method(EC simulation)

Post by kiriru » Thu Jan 16, 2020 4:46 pm

Dear Hydrus community,

I want to simulate "EC(dS/m)".

In my simulations, soil salt (the factor for EC) comes from two sources: precipitation and groundwater. There is no irrigation.
So I entered the same values except on days when the precipitation was zero. (Eg 0.5)
I think that cTop input is good in the above method.

My question is about cBot.
I want to consider salinity from groundwater, but I don't know how to enter it.
Is it enough to give a value when the height of the groundwater exceeds a certain level?

Jirka
Posts: 4983
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: cBot input method(EC simulation)

Post by Jirka » Thu Jan 16, 2020 9:44 pm

That depends what bottom boundary condition you use. If you use the pressure head BC (i.e., you specify the position of groundwater table, then you should use the Dirichlet BC and groundwater EC for cBot. If you use a free drainage BC, then cBot is not used.

kiriru
Posts: 7
Joined: Fri Dec 13, 2019 4:42 pm
Location: Japan

Re: cBot input method(EC simulation)

Post by kiriru » Fri Jan 17, 2020 1:09 am

The boundary conditions are set as follows:
Water Flow BC
Upper:Atmospheric BC with Surface Layer Lower:Variable Pressure Head
Solute Transport BC
Upper:Concentration Flux BC Lower:Concentration BC

The measured groundwater EC was input to cBot, and the result was the same as when the input values ​​were all zero(cBot).
What causes this result?

Jirka
Posts: 4983
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: cBot input method(EC simulation)

Post by Jirka » Fri Jan 17, 2020 1:47 am

That cannot be true. If you have at the bottom Variable Pressure Head and Concentration BC, the program will honor the bottom pressure head as well as the bottom concentration. J.

kiriru
Posts: 7
Joined: Fri Dec 13, 2019 4:42 pm
Location: Japan

Re: cBot input method(EC simulation)

Post by kiriru » Fri Jan 17, 2020 7:10 am

I'm sorry.
There was an incorrect way to represent groundwater levels in simulations.
It is changing steadily.

Thank you very much for your help.

Jirka
Posts: 4983
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: cBot input method(EC simulation)

Post by Jirka » Fri Jan 17, 2020 5:19 pm

No problem. Good luck with the simulations. Jirka

kiriru
Posts: 7
Joined: Fri Dec 13, 2019 4:42 pm
Location: Japan

Re: cBot input method(EC simulation)

Post by kiriru » Sun Jan 19, 2020 4:47 pm

Thank you very much.
I want to ask the last question

I have never seen a simulation that puts data into a cBot.
Can I insert groundwater EC directly into cBot?
In that case, the concentration is too high in my simulation results.

Should I convert "groundwater EC" to be input to "cBot"? (Example, EC * 1/1000)

Jirka
Posts: 4983
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: cBot input method(EC simulation)

Post by Jirka » Sun Jan 19, 2020 7:56 pm

cBot should be directly the concentration of groundwater, without any adjustments and conversions. You need to have consistent units for all input concentrations, i.e., initial and boundary concentrations. In US, we usually express EC in dS/m. J.

kiriru
Posts: 7
Joined: Fri Dec 13, 2019 4:42 pm
Location: Japan

Re: cBot input method(EC simulation)

Post by kiriru » Wed Jan 22, 2020 9:31 am

Thank you for your reply.

I want to apply it to my own simulation.
Thank you for your advice many times.

Post Reply