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Hello, For a very long time, I have been trying to create a numerical model of an aquifer with complex hydrogeology (by using borehole-to-Ugrid option). I had several layers of 4 different materials. But all my efforts were trash. Because, I have never obtain a successful Modflow-usg run. They never converged. Although wetting option was on, the aquifer had so many dry cells. And these dry cells were always at same locations (not near/at the location of wells). It was meaningless. I couldn't run the PEST. So I decided to make my system more basic and created a one-layer model with HK zones. It worked well without the wetting. I have applied pilot points approach for the calibration. And pest is working because the forward run has a successful result. However, this time the calculated residual is too high. I have done many things to decrease the error. But the best result until now is about 7000 (Sum of Squared Weighted Residual Head+Flow) and for Root mean squared residual it is 16. These values are so big. Interestingly, the computed vs. observed head plot (attached) looks not so bad that there should be a way to fit them to the line. I only have head observations in my hand and I don't have any flow observations data. May this be the problem? Or what may be the problem? Could you please help me on this? I would be so happy to hear your recommendations to lower my calibration error to an acceptable value. Note: The computed heads are higher than the measured heads. The boundary conditions are ; specified head along the coast and GHB condition was assigned to some part of the boundary. The model is steady-state. Thank you! Best, Cansu