Because the groundwater vistas outputs cbb file in binary format. I tried to extract the data using flopy, but I only obtained empty txt file. So I want to use MODFLOWwin32 to run the model. In MODFLOWwin32, I modified the format of output file in Output option, I changed the format of cbb from binary to Ascii and ran the model. But it gave out run-time error F31:WRITE(Unit 50) -. I tried to find the details about this error in MODFLOW manual or in groundwater vistas manual, but I found nothing.
I am thinking that the problem may be caused by the unit number both in nam file and in MODFLOWwin32, but I don't know how to make it correct. Or maybe there is other methods for it.
The error you're receiving suggests that there may be an issue with the file I/O during the simulation run.
Here are a few troubleshooting steps you can take to try to resolve the problem:
Check file permissions: Make sure that the directory where the model files are located is writable. If MODFLOW cannot write to the directory, it might throw this error.
Check unit number: In MODFLOW, unit numbers are used to reference different files. If two files are trying to use the same unit number, it could result in conflicts. Make sure all unit numbers in your .nam file and your MODFLOW configuration are unique and consistent.
Review model size: Sometimes, the model might be too large for the program to handle, particularly when generating ASCII files which can be much larger than binary files. Make sure your computer has enough memory and disk space to accommodate the model output.