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zero flux with lower boundary

Posted: Thu Nov 28, 2013 11:42 pm
by mahardie
I suspect im going to get the same answer to this question...i need to upgrade.
I am trying to simulate a flux meter installed at 30 cm depth which has a permanent -65 cm head to draw water into the device. So when soil potential is between 0 and -65 cm water flows into the device, when soil potential is between -65 cm and -1000+ there is no flow into the device.
However using the constant head boundary water flows from the device into the soil...which i need to prevent.
i looked at BDRC options and saw option two to switch boundary condition to zero flux when GWL>99999
I note in the instructions the comment....
This boundary condition can be used for example for a disc permeameter where the specified head changes to a zero flux during time periods when the permeameter is re-supplied with water. The zero flux is initiated by specifying a value larger than 999999......
can i somehow set a zero flux for matric potentials more negative than -65 cm and flow into the dvice between 0 and -65 cm ??
thanks again.

Re: zero flux with lower boundary

Posted: Fri Nov 29, 2013 12:24 am
by Jirka
Yes, you will get the same answer. Indeed, in HYDRUS (2D/3D), version 2, I have implemented a "Seepage Face with a Specified Pressure Head" (hSeep). If the pressure head at the boundary is smaller than hSeep, there is no flow. A constant pressure head (hSeep) is maintained when the pressure head would exceed hSeep and the flux across the boundary is allowed, calculated, and reported. J.

Re: zero flux with lower boundary

Posted: Fri Nov 29, 2013 1:20 am
by mahardie
Thanks again for your help i really appreciate it :D .
i really need to find a way to upgrade. The problem have is that CSIRO (a seperate orgaisation to UTAS) arnt that keen to upgrade the site licence, which means I have to buy a single licence outright, which my work wont support as they see I have a perfectly working old version. if i had a existing single site licence I would upgrade tomorrow.............. :(