Re: What is the acceptable range of mean of residuals, standard error and variance for a regional scale model?

[Ishita Bhatnagar]

Dear All

Just so you know, I do not intend to predict groundwater flow using this model. Thus, in such a case, do you think these statistical measures are acceptable?

Thanks and Regards

ISHITA BHATNAGAR
Research Scholar (Water Resources Engineering)
Department of Civil Engineering
Indian Institute of Technology (IIT)  Delhi
Alternate Email: cez1...@civil.iitd.ac.in
Ph no.: +91 8394834109

On Mon, 27 May 2024 at 15:13, Ishita Bhatnagar <ishitabha...@gmail.com> wrote:

Dear All

I am setting up a regional-scale steady and transient groundwater flow model over an area of 0.4 million sqkm area in Modflow with a grid size is 2km by 3km. I have limited observation points (just 500-600 points); thus, it is difficult to provide distributed parametrization and opt for pilot point calibration. Therefore, I am targeting minimizing the average head residuals for each zone. However, this, too, is very challenging. For instance, for my steady-state model, I could boil down to an overall mean residual of 2.99m after extensive manual and steady-state PEST calibration. Still, the standard error is 24.03 m, and the variance of residuals is 577.6. Are these figures acceptable if I only want a zone-wise, well-calibrated model?   

Thanks and Regards

ISHITA BHATNAGAR
Research Scholar (Water Resources Engineering)
Department of Civil Engineering
Indian Institute of Technology (IIT)  Delhi
Alternate Email: cez1...@civil.iitd.ac.in
Ph no.: +91 8394834109

[Ishita Bhatnagar]

[Philip Margarit]

Hi Ishita,

I would really try to employ pilot points here. The number of observations you have should not limit this as the parameters you can’t estimate are almost as important as the ones you can. I would suggest looking into PEST_HP ENSI as that method might be the best suited for your problem and make sure you have realistic upper and lower bounds for your pilot point sets. That should hopefully give you a better calibration. The main thing you need to think about here is how good your model matches the calibration data that matters for the objective of your model and not the general error statistics for the model as a whole. If you aren’t comfortable working from the command line for PEST_HP ENSI, just make sure you use regularization on your pilot points if you are worried PEST won’t behave due to lack of calibration data in areas of your model. 

Philip Margarit

Water Resources Science PhD Candidate

College of Food, Agriculture, and Natural Resources Science 

University of Minnesota, Twin Cities

651-262-3561

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[Ishita Bhatnagar]

Dear Philip,

Thanks for the detailed suggestion. I will definitely look into it. I have one doubt, for pilot point calibration I need to have measured data points for say conductivity (if I am calibrating K), but the problem is that I do not have any such information for my basin. It's a blind fold. Whatever district or state level lumped information I had I used it to generate initial conductivity zones. So that's why I had dropped the idea of pilot points. Let me know if I understood correctly. 

Thanks and Regards
Ishita Bhatnagar
Research Scholar (Water Resources )
Department of Civil Engineering
Indian Institute of Technology Delhi

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[Jakab Andras - Gmail]

See my comments in another thread of this topic.

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