Why are KHV, KVA and KVV all three needed as active modules? - Forum - iMOD
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Why are KHV, KVA and KVV all three needed as active modules?
M. vdW, modified 3 Years ago.
Why are KHV, KVA and KVV all three needed as active modules?
Youngling Posts: 17 Join Date: 7/5/21 Recent Posts
Hello all,
For my iMOD-model I use GeoTOP-layers for which vertical permeability is available as idf-files. The horizontal permeability I calculated from the vertical permeability and an anisotropy factor (in my case, the value 1.43):
horizontal permeability = 1.43 * vertical permeability
What I don’t understand is that my runfile only runs when all three modules KHV (horizontal permeability), KVV (vertical permeability) and KVA (vertical anisotropy) are active, while I expected that only two would be sufficient (‘KHV and KVV’ OR ‘KHV and KVA’) and that the latter combination would create KHV unneeded.
I searched the iMOD manual, the MODFLOW manual and this forum, but did not find a logical explanation.
Anyone who can make this puzzle logical?
Thanks in advance,
Martin
For my iMOD-model I use GeoTOP-layers for which vertical permeability is available as idf-files. The horizontal permeability I calculated from the vertical permeability and an anisotropy factor (in my case, the value 1.43):
horizontal permeability = 1.43 * vertical permeability
What I don’t understand is that my runfile only runs when all three modules KHV (horizontal permeability), KVV (vertical permeability) and KVA (vertical anisotropy) are active, while I expected that only two would be sufficient (‘KHV and KVV’ OR ‘KHV and KVA’) and that the latter combination would create KHV unneeded.
I searched the iMOD manual, the MODFLOW manual and this forum, but did not find a logical explanation.
Anyone who can make this puzzle logical?
Thanks in advance,
Martin
Frans Roelofsen, modified 3 Years ago.
RE: Why are KHV, KVA and KVV all three needed as active modules?
Padawan Posts: 51 Join Date: 11/11/13 Recent Posts
Hi Martin,
Perhaps chapter 12.8 in the iMOD manual can help answering your question. Especially figure 12.3. The parameter KVV for vertical permeability is defined for aquitards only, so the thickness between BOT1 en TOP2. The parameter KVA is defined for the aquifer only. In your case you use GEOTOP for the geohydrological model. In that model, the layers nicely connect, so no aquitards are defined. In that case you can set KVV to 1.0 while it is not used. .
Kind regards,
Frans
Perhaps chapter 12.8 in the iMOD manual can help answering your question. Especially figure 12.3. The parameter KVV for vertical permeability is defined for aquitards only, so the thickness between BOT1 en TOP2. The parameter KVA is defined for the aquifer only. In your case you use GEOTOP for the geohydrological model. In that model, the layers nicely connect, so no aquitards are defined. In that case you can set KVV to 1.0 while it is not used. .
Kind regards,
Frans
M. vdW, modified 3 Years ago.
RE: Why are KHV, KVA and KVV all three needed as active modules?
Youngling Posts: 17 Join Date: 7/5/21 Recent Posts
Hello Frans,
Thanks for your clear answer.
So for the GeoTOP layers I
- use the available KH-values;
- set KVV to 1.0
- set KVA to 1/1.43=0.7 ? (1.43 is my anisotropy value.)
Example: KHV = 10.0 m/d, vertical permeability will be calculated as 7.0 m/day.
Thanks in advance again.
Martin
Thanks for your clear answer.
So for the GeoTOP layers I
- use the available KH-values;
- set KVV to 1.0
- set KVA to 1/1.43=0.7 ? (1.43 is my anisotropy value.)
Example: KHV = 10.0 m/d, vertical permeability will be calculated as 7.0 m/day.
Thanks in advance again.
Martin
M. vdW, modified 3 Years ago.
RE: Why are KHV, KVA and KVV all three needed as active modules?
Youngling Posts: 17 Join Date: 7/5/21 Recent Posts
Hello Frans,
I tested the effect of KVA by making KVA 10 times smaller (changed KVA value from 0.7 to 0.07): 3D flowlines showed that this smaller KVA value led to more horizontal flow because of the lower vertical permeability.
So KVA value is the ratio of vertical permeability to horizontal permeability.
Issue 'Solved'.
Perhaps you can organise that an example is added to the manual to avoid misinterpretation?
Thanks in advance again.
Martin
I tested the effect of KVA by making KVA 10 times smaller (changed KVA value from 0.7 to 0.07): 3D flowlines showed that this smaller KVA value led to more horizontal flow because of the lower vertical permeability.
So KVA value is the ratio of vertical permeability to horizontal permeability.
Issue 'Solved'.
Perhaps you can organise that an example is added to the manual to avoid misinterpretation?
Thanks in advance again.
Martin
Frans Roelofsen, modified 3 Years ago.
RE: Why are KHV, KVA and KVV all three needed as active modules? (Answer)
Padawan Posts: 51 Join Date: 11/11/13 Recent Posts
Hi Martin,
Your example to calculate vertical permeability is correct as is the definition of KVA.
Thanks for your reply. We close this issue.
Kind regards,
Frans
Your example to calculate vertical permeability is correct as is the definition of KVA.
Thanks for your reply. We close this issue.
Kind regards,
Frans