The modular finite-difference groundwater
flow model (MODFLOW) developed
by the U.S. Geological Survey (USGS) is
a computer program for simulating common
features in ground-water systems
(McDonald and Harbaugh, 1988;
Harbaugh and McDonald, 1996). The
program was constructed in the early
1980’s and has continually evolved since
then with development of many new
packages and related programs for groundwater
studies. Currently, MODFLOW is the
most widely used program in the world for
simulating ground-water flow. The
popularity of the program is attributed
to the following factors