https://www.usgs.gov/publications/modflow-2000-us-geological-survey-modular-ground-water-model-user-guide-lmt6-package
MODFLOW-2000, the U.S. Geological Survey modular ground-water model: User guide to the LMT6...
MODFLOW-2000, the newest version of MODFLOW, is a computer program that numerically solves the three-dimensional ground-water flow equation for a porous medium...