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# CCF_mag calculation

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I am curious how GMS calculates the magnitude of flux in the CCF files. From my understanding, the magnitude of flux of a grid should be the summation of the flux from the 6 faces bounding the grid. However, it seems the value from the CCF-Mag file does not match this value. Anybody has an idea why this happens?

Here is an example:

i ,j ,K ,Front ,Right ,Bottom ,CCF_Mag

1 ,1 ,1 ,0 ,4.83 ,0 ,4.83

1 ,2 ,1 ,-1.10E-03 ,6.59 ,-1.82 ,12

1 ,3 ,1 ,-7.65E-03 ,6.61 ,-6.86E-02 ,13

Take the grid (1,2,1) for example, the flow from back and upper faces are 0, because this is the first row, and first layer, and no recharge or precipitation. Then the flux calculation is the summation of front, right, bottom and left faces, which is

Flux = -0.0011+6.59-1.82-4.83 =- 0.061. But the value from CCF_Mag file is 12.

Edited by James
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• 2 weeks later...

GMS reads the "RIGHT", "FRONT", and "BOTTOM" components of flow from the CCF file. These become the x, y, and z components of the vector data set. The magnitude is computed by as you would for any vector SQRT( x^2 + y^2 + z^2).

If you read in the MODFLOW Grid tutorial sample files and select the cell with I=1, J=15, and K=1 and then you select the Flow Budget command, you will see the following flow components for this cell:

Top 0.0 0.0

Bottom 0.0 -293.7246398926

Left 0.0 -813.8596801758

Right 0.0 0.0

Back 0.0 0.0

Front 0.0 -982.7542724609

When I generate vectors from this CCF data set I get the following vector components for this cell:

VX VY VZ

-813.86 -982.754 -293.725

and a magnitude of 1309.369

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