Procedures and computer programs for telescopic mesh refinement using MODFLOW

Ground-water models are commonly used to evaluate flow systems in areas that are small
relative to entire aquifer systems. In many of these analyses, simulation of the entire flow system
is not desirable or will not allow sufficient detail in the area of interest. The procedure of telescopic
mesh refinement allows use of a small, detailed model in the area of interest by taking boundary
conditions from a larger model that encompasses the model in the area of interest. Some previous
studies have used telescopic mesh refinement; however, better procedures are needed in carrying
out telescopic mesh refinement using the U.S. Geological Survey ground-water flow model,
referred to as MODFLOW. This report presents general procedures and three computer programs
for use in telescopic mesh refinement with MODFLOW. The first computer program, MODTMR,
constructs MODFLOW data sets for a local or embedded model using MODFLOW data sets and
simulation results from a regional or encompassing model. The second computer program,
TMRDIFF, provides a means of comparing head or drawdown in the local model with head or
drawdown in the corresponding area of the regional model. The third program, RIVGRID,
provides a means of constructing data sets for the River Package, Drain Package, General-Head
Boundary Package, and Stream Package for regional and local models using grid-independent data
specifying locations of these features. RIVGRID may be needed in some applications of telescopic
mesh refinement because regional-model data sets do not contain enough information on locations
of head-dependent flow features to properly locate the features in local models. The program is a
general utility program that can be used in constructing data sets for head-dependent flow packages
for any MODFLOW model under construction.