[GRASSLIST:1369] Re: GRASS integration with MODFLOW

[Rick Gagne]

On Wed, 17 Jan 2001 06:06:10 -0800 (PST), Mark Boris wrote:

>I am not a modflow 'guru', but here are a few of my
>findings resulting from attempting to use modflow
>to model electric flow.
>
>Modflow96 compiles quite well under linux so I assume
>that it also compiles well under other unices.  The 
>egcs fortran compiler is what I used.

Great!

>issue that you will run into though, is the size of
>the data that you are planning to process.  You must
>change the size of the 'LENX' variable in the
>modflow.f 
>source file to allow for a larger grid.  But there is 
>a limit of how large you can practically make an input
>dataset.  I found that about 200x200x80 was about
>the largest grid that would run in a reasonable amount
>of time on a PIII800MHz with 512meg RAM.  I would 
>suggest compiling modflow and making some dummy 
>datasets of approximately the same size as what you 
>would be using and see how long it would take to run.
>Note that a model with many layers/inhomogenaities
>takes longer to converge than a simple model.

That's why I was thinking of modeling the study area at various scales.


>IMHO, use modflow96 since you can use free-formatted
>input data files.  If you have to convert GRASS files
>to modflow files, you probably do not want to have to 
>worry about the fixed-fortran format required for
>modflow88.  Writing C apps or scripts to convert grass
>files (or grass data exported to ascii) to modflow
>should be pretty straightforward.

However, we must keep in mind that there is the problem of grid orientation and 
variable grid size, which are necessary to accomodate geologic fabric 
(heterogeneity and hydraulic anisotropy) and to improve convergence at 
pumping wells or other groundwater sinks.


>it myself yet.  I am planning to investigate the
>integration of grass with modflow/matlab/others over
>the summer; I can let you know what I come up with
>if you are still interested at that point.

I suspect that I will. Lets keep in touch.



Regards,

        Rick

RG Hydro-Environmental Ltd.
WaterWatch ..... independent groundwater research

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