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?

## cBot input method(EC simulation)

### Re: cBot input method(EC simulation)

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.

### Re: cBot input method(EC simulation)

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?

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?

### Re: cBot input method(EC simulation)

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.

### Re: cBot input method(EC simulation)

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.

There was an incorrect way to represent groundwater levels in simulations.

It is changing steadily.

Thank you very much for your help.

### Re: cBot input method(EC simulation)

No problem. Good luck with the simulations. Jirka