Online Guide to MODFLOW-LGR

The Boundary Flow and Head (BFH) Package reads input data from the file indicated in the Name file as described by Harbaugh and others (2000, p. 7, 43) using the File Type BFH. Input for the BFH Package is created by LGR and requires that the coupling boundary conditions calculated by LGR be saved using variable IUCBHSV and (or) IUPBFSV of the LGR input file. For an independent child model simulation, IUCBHSV needs to be nonzero; for an independent parent model simulation, IUPBFSV needs to be nonzero.

The BFH Package and LGR cannot be used simultaneously. Thus, when using LGR, the Name file specified in the LGR control file cannot use file type BFH.

The procedure needed to run independent child or parent models with LGR boundary conditions is as follows:

1.Use LGR to calculate and save the coupling boundary conditions.

2.Activate the BFH Package in the Name file with a file name that corresponds to the file saved on IUCBHSV or IUPBFSV for child and parent simulations, respectively.

As discussed in the Running the Parent and Child Model Independently Using the Boundary Flow and Head (BFH) Package section, the BFH package can be used to evaluate the effects of model changes on the boundary conditions. In this case, the complementary boundary conditions also need to be saved when running LGR. For the child model, IUPBFSV needs be nonzero; for the parent model, IUCBHSV needs to be nonzero. If the file containing the complementary boundary conditions for the child or parent models is opened in the Name file on the unit number corresponding to IUPBFSV or IUCBHSV, respectively, then the BFH package will evaluate the discrepancies in the complementary boundary conditions.

Each of these files contains a header record and a list of the child and parent cells involved in the coupling, indicated by the layer, row, and column. For the child models, the corresponding adjoining parent cells and a node index is listed with each child cell. This is followed by a listing of the boundary head or flux values, corresponding to these cells, for each time step.

Example BFH Inputs

The options for the BFH Package can be controlled through inputs to LGR and the Name files. Using the three-dimensional example 3 in Appendix 1, a simulation using LGR is performed first. For an independent simulation of the child grid, the coupling boundary condition (specified head) is saved on unit 80 and the complementary boundary condition (boundary flux) is saved on unit 81.

The Name file for the child grid for the LGR simulation is:

LIST 26 ex3_child.out

BAS6 2 ex3_child.ba6

BCF6 21 ex3_child.bc6

DIS 29 ex3_child.dis

OC 20 ex3_child.oc

DATA(BINARY) 31 ex3_child.hed

DATA(BINARY) 41 ex3_child.flw

PCG 22 ex3_child_3.pcg

RIV 25 ex3_child.riv

DATA 80 ex3_child_bfh.hed

DATA 81 ex3_child_bfh.flw

DATA 51 ex3_child.bot

After successful completion of an LGR simulation, the child model can be simulated independently using the BFH Package. Only the Name file of the child grid needs to be modified. Activate BFH with a file name corresponding to the file where the coupling boundary conditions were saved. Although not required, in the example above, the complimentary boundary conditions were saved. If this file is opened in the Name file on the same unit number on which it was saved, the BFH Package will report any changes in the boundary fluxes of the child model. This is done in the example below. Use of # in the first column results in the line being ignored. This example is for MODFLOW-LGR1. For MODFLOW-LGR2, The file type BFH would be replaces with BFH2.

LIST 26 ex3_child.out

BAS6 2 ex3_child.ba6

BCF6 21 ex3_child.bc6

DIS 29 ex3_child.dis

OC 20 ex3_child.oc

DATA(BINARY) 31 ex3_child.hed

DATA(BINARY) 41 ex3_child.flw

PCG 22 ex3_child_3.pcg

RIV 25 ex3_child.riv

BFH 80 ex3_child_bfh.hed

#DATA 80 ex3_child_bfh.hed

DATA 81 ex3_child_bfh.flw

DATA 51 ex3_child.bot