Main Data File

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The main data file is used by MODPATH and MODPATH-PLOT to define most of the basic elements of the MODPATH simulation. Although most of the data in this file is used by both MODPATH and MODPATH-PLOT, some data is specific to one program or the other. MODPATH and MODPATH-PLOT are designed to read data from a single main data file. Each of the programs ignores those data items that are specific to the other program. The MODPATH main data file is opened in the Name file as type MAIN.

The main data file consists of 6 data items:

•Item 1 -- Specifications

•Item 2 -- Options

•Item 3 -- Confining Bed Codes

•Item 4 -- Boundary Array

•Item 5 -- Porosity

•Item 6 -- Stress Period and Time Step Data

Data item 6 is omitted for steady-state simulations. Detailed instructions for these data items follow.

 

Data Set

Description

1

MAXSIZ HNOFLO  HDRY  NPART  IRCHTP  IEVTTP

MAXSIZ-- is the maximum allowed size (in bytes) of the Composite Budget File.

If MAXSIZ = 0, the program uses a default value that is set in the MODPATH main program. The default value can be changed by resetting the MAXSIZ value in the MODPATH main program and then recompiling the source code. If a transient MODPATH run will generate a composite budget file larger than MAXSIZ, a warning message is issued and an option is provided to either quit or proceed.

The default value of MAXSIZ is 15,000,000.

HNOFLO-- is the value specified in MODFLOW to represent head in inactive cells.

HDRY-- is the head assigned by MODFLOW to cells that have gone dry. If the original version of MODFLOW was used with the BCF1 package, HDRY should be set to "1.0E+30". If the BCF2 package was used in the MODFLOW simulation, HDRY must equal the value specified in the MODFLOW simulation.

NPART-- is the maximum number of particles allowed for a MODPATH run. The value of NPART has no effect in MODPATH-PLOT. If NPART is omitted or set equal to 0, MODPATH  automatically resets NPART to a default value that is defined in the MODPATH main program. For the standard version of the MODPATH source code, there is no advantage to setting NPART to a value other than 0 because array memory is not allocated dynamically. However, providing the variable NPART makes it relatively easy to take advantage of FORTRAN compilers that allow arrays to be dimensioned dynamically at runtime. The use of dynamic memory allocation requires that MODPATH’s main source program be modified as appropriate for each specific FORTRAN compiler.

The default value is 500,000.

IRCHTP indicates where recharge (if used in the model) is applied

•0 - recharge is treated as an internal source.

•not 0 - recharge is assigned as a vertical component of flow to the top face.

IEVTTP indicates where evapotranspiration (if used in the model) is applied

•0 - ET is treated as an internal sink.

•not 0 - ET is assigned as a vertical component of flow to the top face.

2

Options-- is a 1-line character record that may contain one or more keyword codes that control options in MODPATH and MODPATH-PLOT. A blank line must be included for this data item even if none of the keyword options is used. Keywords that only affect MODPATHPLOT are ignored by MODPATH.

XSECTION indicates that the model is a 1-row cross section for which IBOUND and the Grid Unit Array (GUA) should each be read as a single, 2-dimensional array with dimensions of NCOL and NLAY.

COMPACT indicates that MODPATH should generate endpoint, pathline, and time series files as text files using the global node number to indicate cell location. If COMPACT is omitted, the cell location is designated using the row-column-layer grid indices (as in previous versions of MODPATH).

BINARY indicates that the endpoint, pathline, and time series files will be generated by MODPATH in binary form. This keyword also is required by MODPATH-PLOT in order to correctly read binary versions of these files.

METERS indicates to MODPATH-PLOT that distances are in meters. The METERS parameter only affects the label on the distance scale produced by MODPATH-PLOT. It has no affect on computations produced by MODPATH. If the option METERS is not specified, MODPATH assumes that length units are in feet. If a length unit other than feet or meters is used in MODFLOW, the scaling performed by MODPATH-PLOT will not be correct.

WT(OFF) indicates that the water table profile will not be drawn on true cross section plots. If none of the three "WT" options is specified, MODPATH-PLOT draws the water-table profile as a solid line with the same color used for drawing contour lines.

WT(DOTTED) indicates that the water-table profile will be drawn as a dotted line on true cross section plots.

WT(DASHED) indicates that the water-table profile will be drawn as a dashed line on true cross section plots.

3

•0 indicates confined

•not 0 indicates convertible or water table

4

Read one array for each layer

In the current version of MODFLOW, the IBOUND array is read one layer at a time by specifying a 2-D array of data for each layer in the grid. In this version of MODPATH, if the model is a 1-row cross section and the keyword XSECTION is specified in the options data record (Main data file item 2), the IBOUND array will be read as a single 2-D array for the entire cross section. Future versions of MODFLOW may support the XSECTION option for IBOUND data in cross sectional models.

If this IS NOT a 1-row cross section, read a 2-D array of data for each layer by repeating the following data sequence for each layer:

3. IBOUND(NCOL,NROW)

FORMAT: 2-D integer array reader (U2DINT)

Or, if this IS a 1-row cross section with XSECTION specified, read a single 2-D array for the cross section:

3. IBOUND(NCOL,NLAY)

FORMAT: 2-D integer array reader (U2DINT)

IBOUND-- is the boundary array containing cell type codes.

•IBOUND < 0 : specified head cell

•IBOUND = 0 : inactive cell

•IBOUND > 0 : active cell

The absolute value of IBOUND is the zone code, which is used by MODPATH-PLOT to determine the color of pathlines and particle points. MODPATH requires that the absolute value of IBOUND be less than 1000.

5

Read one array for each layer

REPEAT THE FOLLOWING DATA IN SEQUENCE FOR EACH LAYER:

5A. POR(NCOL,NROW)

FORMAT: 2-D real array reader (U2DREL)

If the model layer has a quasi-3d confining layer, then

5B. PorCB(NCOL,NROW)

FORMAT: 2-D real array reader (U2DREL)

POR-- is the array containing porosity values for a model layer.

PorCB-- is the array containing porosity values for a quasi-3D confining layer associated with the model layer. If a model layer includes a quasi-3d confining layer, the PorCB array immediately follows the POR array for that model layer.

Items 6A and 6B are required only for transient simulations:

6a

TBEGIN-- is the time value assigned to the beginning of the MODFLOW simulation. Any convenient value may be specified, including values less than zero.

6b

BeginPeriod  BeginStep  EndPeriod  EndStep

Data item 6b marks the range of time steps that will be processed from the MODFLOW cell-bycell budget file and used to generate the MODPATH composite budget file. The MODFLOW cell-by-cell budget file must contain data for all of the time steps within the range specified in data item 6b. The MODFLOW cell-by-cell budget file also may contain data for time steps that are outside of the specified range.

BeginPeriod, BeginStep-- the stress period and time step of the first time step in the block of time steps that will be processed. If any stress period in the model is a steady-state stress period, BeginPeriod and BeginStep must both be 1.

EndPeriod, EndStep-- the stress period and time step of the last time step in the block of time steps that will be processed.

Item 6b is not read if the MODPATH analysis uses an existing composite budget file.