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Michal

Export native modflow files with Pilot Points

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Hello,

I have encountered a problem with exporting native modflow files from GMS. Some of the model parameters are defined using Pilot points. Lets say that I would like to use different version of MODFLOW to calibrate the model. I have succesfully exported the MODFLOW native files and I was able to start USGS version of modflow. The input data are read correctly, first stress period is solved, however during the second period MODFLOW stops. Here is the end of the output file:

 

PERCENT DISCREPANCY =          -0.03     PERCENT DISCREPANCY =          -0.03






         TIME SUMMARY AT END OF TIME STEP    1 IN STRESS PERIOD    1
                    SECONDS     MINUTES      HOURS       DAYS        YEARS
                    -----------------------------------------------------------
   TIME STEP LENGTH 2.67840E+06  44640.      744.00      31.000     8.48734E-02
 STRESS PERIOD TIME 2.67840E+06  44640.      744.00      31.000     8.48734E-02
         TOTAL TIME 2.67840E+06  44640.      744.00      31.000     8.48734E-02
1
1
                            STRESS PERIOD NO.    2, LENGTH =   29.00000    
                            -----------------------------------------------

                              NUMBER OF TIME STEPS =     1

                               MULTIPLIER FOR DELT =     1.000

                            INITIAL TIME STEP SIZE =   29.00000    

 PARAMETER "sc1v1     " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

 PARAMETER "sc1v2     " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

 PARAMETER "sc1v3     " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

 PARAMETER "sc1v4     " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION
 
....

 PARAMETER "GHB_3405  " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

 PARAMETER "GHB_3409  " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

 PARAMETER "GHB_3406  " IN PARAMETER INPUT FILE HAS NOT BEEN DEFINED
 -- STOP EXECUTION

When modflow starts no interpolation is performed for the pilot points. I assume there is some custom routine in the GMS version that handles the interpolation from PP to the MF grid array. Please advice how this is supposed to be handled or what am I doing wrong.

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Hi Michal -- I've had this same problem. What I've done is interpolate the pilot point values to a 2-D grid (hopefully, the same as the model 3-D grid) and then import the interpolated values into the corresponding model layer input. For example, horizontal hydraulic conductivity pilot points for the models surficial layer are interpolated to the 2-D grid then in your MODFLOW package, use the "2D Dataset -> Layer" command to place the interpolated horizontal hydraulic conductivity values into layer 1 of the model. Do this for all of your pilot point sets. Remove all other PEST variables, set up the GMS files for a forward run and try the export to native text again. From what I've seen, GMS does not export files with PEST inputs.   

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Thank you for your answer. Unfortunately this is not a solution to the problem, because you lose model parameterization. In my opinion it would be best if, when exporting native modflow files with parameters defined using pilot points, GMS writes also PEST "pilot point file" and "structure file". It could then write model BAT file with appropriate PEST utility programs involved prior modflow run, like  PPK2FAC, FAC2REAL and REPARRAY. Such approach would allow parameter estimation using PEST.

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Hi Michal -- I do all of my pest work outside of GMS. I set up the pilot points and other variables in GMS, save and run the files - up to the point where the *.PST file is written. I stop the execution in GMS and do all of the PEST work in DOS prompt windows. The *.PST file usually requires extensive edits but when I get in all back together, PEST works fine.

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Yes, this is my a workflow too. There are useful utility programs in PEST to use with pilot points, like PPKREG1 and VERTREG. The native PEST approach to pilot points is necessary to use with these programs.

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