User's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model

A number of changes have been made to the U.S. Geological Survey modular finite-difference ground-water flow model, which is commonly known as MODFLOW. Existing MODFLOW input files will work with the revised model. Also, the basic structure and computational methods of the model have been maintained. Those familiar with the original model should have no difficulty adapting to the revised model. Some of the most significant changes are: