representing geology with rasters?

[T.W.CHARNOCK]

Hi  Grasshoppers

thanks to everyone who replied to my question about boreholes a few
weeks ago.

I am trying to link GRASS to a ground-water flow model.  At the
moment am a considering the problem of representing geology within
the GRASS database. The model I am using divides the geology up into
3d cells with constant properties (eg hydraulic conductivity) within a
cell.  Rasters are two dimensional, so the only two ways I can see of
representing geology are as a series of planar slices through the
geology,  or as a series of "DEMS" following strategraphic surfaces.
Either way I can see a lot of problems looming, particularly with
maintaining consistency between raster layers as GRASS has no way
(that I know) of linking rasters except by giving them sensible
names; eg layer_1 layer_2 etc

At the moment I favour using strategraphic surfaces as this fits the
model I am using most closely, and GRASS is quite rich with surface
interpolation routines.  I am concern however that when I
change region, resampling will lead to layers intersecting, a kind of
3d analogy to the problem of slivers in vector data.
my head hurts :-(

Has anyone addressed this problem before?

You can probably tell I'm no geologist or database engineer, comments,
discussion and references welcome :-)

much cheer    Tom.

Tom Charnock               
Dept Civil Engineering     
Aston University          
Birmingham B7 5NJ UK                           
charnotw at aston.ac.uk