Computer Programs for Telescopic Mesh Refinement using MODFLOW-96: MODTMR, TMRDIFF, and RIVGRID

Documentation

Leake, S.A., and Claar, D.V., 1999, Procedures and computer programs for telescopic mesh refinement using MODFLOW: U.S. Geological Survey Open-File Report 99-238, 53 p.

MODTMR

• ABSTRACT — The purpose of MODTMR is to construct data sets for local models embedded within regional models constructed with MODFLOW-96 (Harbaugh and McDonald, 1996). MODTMR allows construction of local-model data sets that specify perimeter boundary conditions of embedded models, and local-model data sets for most MODFLOW packages. Major features of the program are as follows: (1) MODTMR is self contained and will run on a variety of computer types and operating systems. (2) Combinations of flow and head boundary conditions can be specified on the perimeters of local models. (3) Local-model grids can be at any angle to regional-model grids. (4) Local models can include a subset of layers in regional models. (5) Some regional-model layers can be subdivided into multiple layers in local models.

• METHOD — MODTMR carries out construction of local model data sets in two steps. The first step is to construct local-model perimeter boundary condition data sets, and the second step is to construct all other local-model MODFLOW data sets. Values of parameters and boundary conditions for local models are computed using a variety of interpolation techniques. For details, see the Documentation report (Leake and Claar, 1999).

• HISTORY — Version 1.0 99/11/01 - Original published version Version 1.1 2001/05/16 - Corrected several errors, redimensioned main array. See file Revisions.txt in distribution for details.

• DATA REQUIREMENTS — The user is must construct An input data set that includes information on the regional and local models and specification of how the local model is to be constructed. Other requirements are as follows: (1) Regional-model input data sets compatible with MODFLOW-96 with no Fortran unit numbers in the range of 90-99 and including a regional-model Output Control data set that specifies 'COMPACT BUDGET FILES'. (2) Unformatted flow and head terms from steady-state or steady- state and transient regional-model simulations, (3) An executable version of TMRDIFF that was compiled with the a FORTRAN compiler compatible with that used to compile the executable version of MODFLOW-96 used to run the regional model.

• OUTPUT OPTIONS — The output is one or more MODFLOW data sets for a local model.

• SYSTEM REQUIREMENTS — MODTMR is written in Fortran 77. The code has been used on Windows/ MS-DOS- and UNIX-based computers.

TMRDIFF

• ABSTRACT — The purpose of program TMRDIFF is to provide a means of comparing head and drawdown in a local model with head and drawdown in the corresponding area of the regional model. Because local- and regional-model grid spacing is different, head and drawdown are not computed at the same locations in the two models. The program provides output for the two models with head and drawdown calculated at the same points.

• METHOD — Program TMRDIFF reads computed output from local and regional simulations and writes information on head and drawdown for selected cells in the local model grid and selected time steps and stress periods. Interpolation methods used by program MODTMR are used to compute the head or drawdown values. For details, see the Documentation report (Leake and Claar, 1999).

• HISTORY — Version 1.0 99/11/01 - Original published version Version 1.1 2000/05/04 - Corrected an error. See file Revisions.txt in distribution for details.

• DATA REQUIREMENTS — Use of TMRDIFF requires a regional model and a local model created program MODTMR, the corresponding MODTMR input data set, and files with appropriate head or drawdown arrays saved from the regional- and local-model simulations. All other input to TMRDIFF is interactive.

• OUTPUT OPTIONS — The information written can be (1) arrays of head or drawdown for a specified model layer, stress period, and time step, or (2) time series of head or drawdown for selected local-model layer, row, and column locations for all simulation times at which information was saved from simulations of the local and regional models. For either (1) or (2), output consists of (A) head or drawdown in the local model, (B) head or drawdown in the regional model, and (C) difference between local-model and regional-model head or drawdown.

• SYSTEM REQUIREMENTS — TMRDIFF is written in Fortran 77. The code has been used on Windows/ MS-DOS- and UNIX-based computers.

RIVGRID

• ABSTRACT — The purpose of RIVGRID is to construct MODFLOW data sets for any or all of the River Package, the Drain Package, the General-Head Boundary Package, and the Stream Package. The programs uses coordinates of traces of features such as rivers, streams, and drains; properties at selected locations along the features; and infomation on model grid location and spacing to construct the data sets. RIVGRID can be used in applications of telescopic mesh refinement or separately to construct data sets for any MODFLOW model.

• METHOD — For program RIVGRID, rivers, drains, general-head boundaries, and streams are assumed to be groups of continuous surface-water features. Within each group, part or all of a continuous feature is represented by series of vertices that define the trace of the feature projected onto a horizontal surface. A series of vertices that represents a single continuous surface-water feature is called a segment. Although only the MODFLOW Stream Package requires data input by segment, program RIVGRID also applies the concept of segments in defining locations of rivers, drains, and general-head boundaries. With information on vertices of features and on the location, angle, and spacing of the grid, RIVGRID carries out the following steps: (1) Rotate, translate, and scale coordinates of all vertices of all segments to a local coordinate system with the origin at the intersection of the outer edges of model row NROW and column 1 (fig. 29). (2) Add vertices to segments where grid lines (row and column boundaries) cross the segments. (3) For model cells traversed by segments, compute and store row and column location, length of the segment within the cell, and the distance along the segment from the start of the segment to the midpoint of the piece of the segment within a cell. Within each segment, properties and conditions needed in constructing MODFLOW data sets are entered at control points. Properties needed for MODFLOW packages for cells along traces of segments are interpolated or extrapolated using values of properties at control points.

• HISTORY — Version 1.0 99/11/01 - Original published version Version 1.1 2000/07/21 - Corrected an errors. Added a statement to write to screen number of segments that were found. See file Revisions.txt in distribution for details.

• DATA REQUIREMENTS — Input to program RIVGRID requires a Main Input Data Set that describes the model grid and specifies which MODFLOW Packages are to be constructed. Upon running program RIVGRID, the user must enter the name of the file containing the Main Input Data Set. For each MODFLOW input package to be constructed, two additional data sets are required, each in a separate file. The first is the Location Data Set. This data set consists of lists of coordinates pairs that define horizontal traces of features to be included in the output MODFLOW data set. Lists of coordinates are grouped by segment and for the Stream Package, the coordinates must start at the upstream location and be listed in downstream order. Coordinates for all segments for a package must be included in the Location Data Set. The second data set required for each package is the Control Data Set. This data set lists information at selected control points along each segment.

• OUTPUT OPTIONS — The output is one or more MODFLOW data sets for a local model.

• SYSTEM REQUIREMENTS — RIVGRID is written in Fortran 77. The code has been used on Windows/ MS-DOS- and UNIX-based computers.