No Flow Boundary Condition

[Hydrology]

Is the default boundary condition in MODFLOW a no flow boundary?  If so how would I create a boundary condition that allows flow, but has a fixed head at either end of the boundary?

[Bri]

The Online Guide to MODFLOW has a page about boundary conditions here.  In short, there are three different boundary condition types, including a specified head boundary condition.

You can look at the GMS Tutorials page for advice on how to set up your boundary conditions, especially in the tutorials labelled "MODFLOW - Conceptual Model Approach."

 

I hope this helps!

[Hydrology]

Hi Bri, thanks for the response.  I am familiar with the references that you indicated.  I often use the specified head and head dependent flux boundaries.  I havent used the specified flux boundary, but that is not what I am looking for.  What I am trying to set up is a boundary condition that will allow free flow across the boundary without restriction, so that the flow across the boundary will vary in time, depending on the amount of water that i pump into or out of the model domain.  I don't want to necessarily fix the head across the boundary either because I think that would overly constrain the model.  Not applying a boundary condition to that part of the model will create a no-flow boundary condition, and that is what i am trying to avoid.  Is there a way to achieve the condition that I am looking for?

[Michal]

Hi, I think that what you describe could be achieved by general head boundary. Without specifying head at the boundary modflow cannot calculate groundwater gradient between the cell and the external region. So I think the problem is unsolvable the way you try to aproach it. I suggest using GHB package. If you have no information about heads outside the model domain, you could for instace specify GHB head the same as some initial model result head and together with lower conductance the head in the boundary condition cells will vary based on pumping/injection in the model domain. For higher conductance values the boundary will resemble constant head boundary while for lower values it will act more as no flow BC. The key is to find the right value which could be achieved through parameter estimation process.

[Hydrology]

Thanks Michal, I will experiment with that and see if that approach gives me what I need.

[ilaria_q]

On 5/6/2019 at 10:27 PM, Hydrology said:

Thanks Michal, I will experiment with that and see if that approach gives me what I need.

Good afternoon,

i have the same problem that you described before ( i need to set the same boundary conditions). how did you manage to solve it?

thanks for your help