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Using TIN data to define layer elevations

Paul Ferguson

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I am trying to use a conceptual model approach to construct a MODFLOW simulation in GMS.

The model has 6 layers and I'd like to use data from two TIN files to define the top and bottom elevations of the layers. TIN #1 represents current topography and will define the top of layer 1. Tin #2 represents pre-mining topography and will define the top of layer 2. Note that the top elevations of layers 3 to 6 will be offset from the top of layer 2 by 5 m, 15 m, 45 m, & 105 m, respectively & the bottom of layer 6 will be 150 m deeper than the top of layer 2.

The reason for the difference in current & pre-mining topography is the presence of mine waste. Layer 1 is comprised of this mine waste and the thickness of the layer represents the difference between the elevations from the two TIN files. I would interpolate the layer elevations using 2D scatter data but my problem is that the x,y values do not match and hence I cannot simply pull the data into GMS and 'Interpolate to MODFLOW Layers'.

I hope this description of the problem is clear but please let me know if I can provide additional details.



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Right click on the required TIN from left hand menu tree and select "Convert to" then "2D scatter points". In the 3D grid module, create a 2D grid by selecting from the top menu "Grid" then "Grid ->2D grid". Interpolate the new scatter point set to the new 2D grid using an appropriate interpolation method. In the Modflow global options, "top elevation" select "2D data set -> layer" and pick the 2D grid you want. If the TINs or scatter points are not a good match then there may be layer overlaps, which can be fixed in the model checker. Alternatively, if you are certain that there are should be no areas without fill or the pre-mining data is sparse (not from historical topo maps but from limited drilling data), then it may be better to interpolate the fill thickness to a TIN or 2D grid, then subtract it from the top of layer 1 to get the top of layer 2 and subsequent layers.

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