"Modifications and corrections to the finite-difference model for simulation of three-dimensional ground-water flow"




             UNITED STATES DEPARTMENT OF THE INTERIOR
                        GEOLOGICAL SURVEY
                        RESTON, VA. 22092

In Reply Refer To:                            November 18, 1982
Mail Stop 411


GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 83.02

Subject:  PUBLICATIONS--"Modifications and corrections to the
                         finite-difference model for simulation of
                         three-dimensional ground-water flow" by
                         Lynn J. Torak

The report accompanying this memorandum describes modifications
that have been incorporated into the finite-difference model for
simulation of three-dimensional ground-water flow by Trescott
(1975) and Trescott and Larson (1976).  These changes extend the
application of this model to problems involving head-dependent
sources and sinks (i.e., rivers, evapotranspiration, and springs
or drains).  Changes were also made which may enhance convergence
of an iterative solution by the Strongly Implicit Procedure (SIP).
This report contains other corrections to the model which
eliminate errors in (a) formulating coefficients for water-table
simulations using the Basic 3-D approach (Equation 3); (b)
formulating coefficients in the vertical direction when the Quasi
3-D approach is taken (Equation 4, Trescott, 1975, with TK values
read in); (c) the computation of vertical flow; and (d) punched
output format of the PHI matrix.

The report first describes the nature of the modifications that
Lynn made to the 3-D model, his personal experiences with their
implementation, and additional data-input instructions.  This is
followed by a description of errors inherent to the 3-D model and
corrections that were made.

This report describes two versions of the 3-D model.  One version
contains the corrections and modifications described in this
report; the other version contains only the corrections to the
standard 3-D model as it is described in Trescott (1975) and
Trescott and Larson (1976).  Both versions reside on the ADMAHL
computer in Reston.  The modified and corrected version of the 3-D
model may be accessed as


DSN=VG4E91L.HEDDDEP.FORTGI.FORT/,UNIT=3330-
1,VOL=SER=SYS312,DISP=SHR

The corrected version of the 3-D model may be accessed as

DSN=VG4E91L.STANDTD.FORTGI.FORT/,UNIT=3330-
1,VOL=SER=SYS010,DISP=SHR


All program statements of modifications and corrections are
identified in these versions by an asterisk (*) or a digit (0-9)
in column 80.  The original program sequence numbers appearing in
columns 73-79 were preserved whenever possible so that a
comparison of the modified and/or corrected version with the
original model can easily be made.

Additional copies of this report are available from the Ground
Water Branch.



                              (s) Eugene P. Patten
                              Acting Chief, Ground Water Branch

Attachment

WRD Distribution:
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FO (with attachment)