There are three main log files (where the xx refers to your document file name). All three of these files are found in the default results directory along with the other result files.
xx_PP_Print.log - This is the main output file from the pre-processor.
xx_WM_Print.log - This is the main output from the water movement engine.
xx_WQ_Print.log - This is the main output from the water quality engine.