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24/05/2016 14:09:20

Hello everyone,

I'm wondering how FloodModeller is dealing with the edges of a computational domain. It seems that the model is accumulating water at the lowest-lying edges. Is it true? Do one has to define a Boundary condition along the edges to allow water to flow out of the domain through the edges of the computational domain?

Thank you in advance.


Best Regards,




24/05/2016 14:43:46

Hi Shrestha,

Water will 'stack up' at the edges of your active area if you have not set up a method to remove this. There are two options:

  1. To increase the size of the active area so the water does not come into contact with the edge of the model.
  2. Create a 2D boundary line and add this to the boundary conditions tab within the .XML and select the normal depth boundary. This will allow water to 'flow' out of your domain.

I hope this helps.




24/05/2016 15:40:27

Hello Rob,

thank you for your reply. 

If I define a 2D polyline boundary along the lowest edge of my domain and select a normal depth boundary, what fixed value of depth should I choose? Should I choose a large value so that all the water reaching the boundary is removed from the domain?

Thank you once again.


Best regards,




25/05/2016 11:40:38

One more thing I just discovered is when I try to use normal depth boundary condition without specifying a polyline shape file to enforce outflow through the domain boundaries, as described in the help file, I could not get it running because the program expects a point shape file for this case and asks to enter X,Y coordinates. A snippet from the FLoodModeller help file looks like below:

Boundary Conditions

    • Normal Depth – calculates the normal depth-flow relationship at a boundary and is usually used as an outflow boundary. The location can be specified by a shapefile (point or polyline) and user-defined slope, or if a shapefile is not specified, it may apply anywhere around the domain boundary. The latter (free location) case is useful when the outflow location is not known a priori, but results should be interpreted with care if there exist multiple outflow locations since the relationship is calculated for the entire domain boundary; in the free location case, the slope is not entered, but calculated as the water surface slope. In either case, the boundary is only activated when water reaches the boundary and the relationship is only calculated using those boundary cells which are wet.

Has anyone experience the same problem? or I am doing something wrong here?

Thank you.


Best regards,



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