Flo-2D Pro – Varying Grid Size for One Simulation

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    We are currently contemplating on purchasing the Pro-version of Flo-2d.

    We are usually handling flood studies for site developments which involves only a small area which is the area of interest. To properly simulate flooding in the area, the computational domain of the study should involve the catchment which extends outside the boundary.

    Given this scenario, our study would focus only on the small area and, thus, will require finer grid sizes compared to those outside of this area but included in the same catchment area.

    Is the Flo-2d Pro-version capable of having different grid sizes for one simulation? If not, Are there any plans in future versions that this will be implemented? If so, is there an approximate date of release?

    Thank you very much.

    Best Regards,



    Hi Luigi,

    FLO-2D cannot use variable grid element sizes at this point. We do have a tool that allows you to capture outflow from an upstream model and use it as inflow to a downstream model.


    And what is that tool or process that allows capturing outflow from one model and using it as inflow to a downstream model?


    I explored a couple of ways to get the desired information. Option 1 is to set the CONT.DAT NOPRTFP to 3 so that the outflow discharge is output to the BASE.OUT for every computational time step. However, the output format would make it laborious to pull together data in a format needed for the INPUT.DAT. Option 2 is to create a cross section, in FPXSECT.DAT or GDS>Tools>Create Floodplain Cross Sections, that is one cell upstream of the outflow cells. The applicable cross section cell information in CROSSQ.OUT can easily be converted into an INFLOW.DAT file for the downstream model. Assuming the downstream model cell size is going smaller requires minor adjustment. For example, if the upstream cells were 200 feet and the downstream cells 50 feet, the CROSSQ.OUT output for an upstream cell would be divided by 4 and used for the 4 adjacent cells in the downstream watershed.

    The “tool” referred to above may be simpler, but short of knowing what that is, this should work. I plan to try it soon on a project. I will report back.


    The tool referred to is in Pro, but the FPXSEC.DAT to CROSSQ.OUT to INFLOW. DAT method described above works well and is fairly simple–I have done it several times.


    The method I was referring to is pretty new. It is in the Pro Model. We have a tutorial and a video with examples. I think it is lesson 13 and the videos are in my FTP site.

    Don’t try to get it with Base.out. It isn’t set up to easily extract data and it makes your run longer. Just keep that variable set to NoPRtfp = 2.

    Floodplain cross sections are your best bet because they are so simple. Their main limitation is if the water is moving around on the floodplain in multiple directions like in an Urban setting. So long as all of the water is moving across the cross section, they work very well.

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