Time-variant hydraulic conductivity in MODFLOW

[Chang Liao]

Hi all,

I have been using MODFLOW for a while and I am definitely sure that this question has been asked before.

But I haven't got an affirmative solution to this. 

So the question is: can we change the HK values within one MODFLOW simulation?

[Giovanni Firmani]

There is no possibility with the all the free versions of modflow. There is a third party version called modflow-surfact developed by hgl that does the job.
If you don't want to buy the licence the only solution is to stop the model every time the k has to be changed.

--
You received this message because you are subscribed to the Google Groups "MODFLOW Users Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to modflow+u...@googlegroups.com.
To post to this group, send email to mod...@googlegroups.com.
Visit this group at https://groups.google.com/group/modflow.
For more options, visit https://groups.google.com/d/optout.

[Ashutosh]

Not possible in modflow!

What kind of concept do you want to model?

Might be that there are some workarounds?

Hpc

Sent from my iPhone

--

[Chang Liao]

So my top layer has some sort of phase change during the winter, and I need to reflect this. UZF is only capable for unsaturated but not good for completely frozen ground I assume.

Yes, as Gio suggested, the only solution is to stop the model every time the k has to be changed.

I guess this is the best way for me to do it now I just wish the model can convergence without much difficulty.

[Chang Liao]

Thanks, I heard that so, too.

I am just curious why there is not such capacity in the official modflow. It should be straightforward to add this feature.

[Chris Nicol]

MODFLOW-USG beta (available with Groundwater Vistas or possibly via the MF-USG author) has the Time-Variant Materials (TVM) package, which does what you are after. 

[Richard B. Winston]

If you are using UZF, I doubt you would be able to do this at all
without modifying the MODFLOW source code. The problem is that the UZF
package stores the water content in the unsaturated zone in an array of
values for each vertical column of cells. However, the input for UZF
only allows you to specify a single value of water content for each
vertical column of cells. Thus, you can't fully define the input for UZF
based on the output from UZF. In addition, UZF doesn't even write the
values that you would need to specify the initial conditions for UZF to
continue a model run even if it were possible to specify them in the input.

Chang Liao wrote:
> So my top layer has some sort of phase change during the winter, and I
> need to reflect this. UZF is only capable for unsaturated but not good
> for completely frozen ground I assume.
> Yes, as Gio suggested, the only solution is to stop the model every
> time the k has to be changed.
> I guess this is the best way for me to do it now I just wish the model
> can convergence without much difficulty.
>
>
> On Sunday, June 12, 2016 at 7:05:49 AM UTC-4, hpc wrote:
>
> Not possible in modflow!
> What kind of concept do you want to model?
> Might be that there are some workarounds?
>
> Hpc
>
>
> Sent from my iPhone
>
> On 11 Jun 2016, at 19:45, Chang Liao <changl...@gmail.com

> <javascript:>> wrote:
>
>> Hi all,
>> I have been using MODFLOW for a while and I am definitely sure
>> that this question has been asked before.
>> But I haven't got an affirmative solution to this.
>> So the question is: can we change the HK values within one
>> MODFLOW simulation?
>> --
>> You received this message because you are subscribed to the
>> Google Groups "MODFLOW Users Group" group.
>> To unsubscribe from this group and stop receiving emails from it,

>> send an email to modflow+u...@googlegroups.com <javascript:>.

>> To post to this group, send email to mod...@googlegroups.com

>> <javascript:>.

>> Visit this group at https://groups.google.com/group/modflow

>> <https://groups.google.com/group/modflow>.

>> For more options, visit https://groups.google.com/d/optout

>> <https://groups.google.com/d/optout>.

>
> --
> You received this message because you are subscribed to the Google
> Groups "MODFLOW Users Group" group.
> To unsubscribe from this group and stop receiving emails from it, send
> an email to modflow+u...@googlegroups.com

> <mailto:modflow+u...@googlegroups.com>.

> To post to this group, send email to mod...@googlegroups.com

> <mailto:mod...@googlegroups.com>.

[None]

As someone above mentioned, the USG version packaged with groundwater vistas has a time variant property capability, which I believe is superior to the surfact version because it handles changes in storage in a mass conservative manner.
You might however review whether this is really necessary. I have found myself wanting to change properties when either it is truly not significant to the model behavior or I can do something similar with changing the boundary conditions.

[Chang Liao]

Thanks for the analysis. 

But I am still a little confused.

According to the online guide:

[THTI (NCOL, NROW)] -- U2DREL

THTI

An array of positive real values used to define the initial water content for each vertical column of cells in units of volume of water at start of simulation to total volume (L3L-3). So I am able to specify the initial water content for the UZF layer, which is the top layer in my model.  Therefore, you were saying that UZF can't output the water content currently according to the guide. And I have to modify the source code if necessary. I can also use external water content data directly.

[Richard Winston]

Note that THTI has a single value for each vertical column of cells. At the end of a simulation, MODFLOW will have an array of values, not a single value, for each column of cells. 

To unsubscribe from this group and stop receiving emails from it, send an email to modflow+u...@googlegroups.com.
To post to this group, send email to mod...@googlegroups.com.