How to simulate the top layer of a multi-aquifer system as aquitard in modelmuse?

[Smaranika Mahapatra]

Dear all,

Greetings! I have a doubt regarding model conceptualization and setup. My area has 4 layers: 1st and 3rd ones are aquitards and 2nd and 4th ones are confined aquifers.

In model muse, the aquitards are treated as non-simulated having only vertical leakage. However, while doing so, it's showing the error "The top layer group must be simulated".  Then, how to set the top aquitard layer in modelmuse? The top aquitard thickness varies from 2 to 35 m having silty-clay or clay type materials. 

I had tried an alternative way by assigning the top aquitard as a convertible layer having very less Kx. But, I am getting very high hydraulic head values for the observation wells. One example is attached for a representative well. I have rechecked the recharge and pumping values as well. Kindly, suggest on this problem.

With best regards,

Smaranika

[Richard B. Winston]

If there is no flow at all through the top layer, you don't need to include it in the model at all.

[Smaranika Mahapatra]

Hi Richard,

There is flow through the layer. Past researchers in that area have also included the top aquitard in their model. 

How to consider this in modelmuse and let the model know that the top layer is an aquitard?

Smaranika

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[Richard B. Winston]

Non-simulated layers were originally included in MODFLOW as a way of reducing the memory requirements when computers  had much less memory than they do now. The option was eliminated from MODFLOW 6 because it is no longer needed.

If you have a low hydraulic conductivity layer at the surface and apply recharge to it, the added water may not go anywhere because the hydraulic conductivity is too low. That might explain the high simulated heads in your model if the observation point was in the recharge layer.

On Apr 25, 2022, at 10:48 PM, Smaranika Mahapatra <smahap...@gmail.com> wrote:

[Smaranika Mahapatra]

Dear Richard,

Thanks a lot. Yes, you were right. I did not really think of the observation points lying within the recharge layer. The hydraulic heads substantially got reduced after I corrected the observation well depths.

With best regards,

Smaranika

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Smaranika Mahapatra
Research Scholar (Land and Water Resources Engineering)
Agricultural and Food Engineering Department
Indian Institute of Technology Kharagpur
West Bengal, 721302