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SOR - Slice-Successive Overrelaxation Package

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SOR - Slice-Successive Overrelaxation Package

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SOR - Slice-Successive Overrelaxation Package

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Abbreviation in Name file



The Slice-Successive Overrelaxation package is used to solve the finite difference equations in each step of a MODFLOW stress period.


Harbaugh, A.W., Banta, E.R., Hill, M.C., and McDonald, M.G., 2000, MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- User guide to modularization concepts and the Ground-Water Flow Process: U.S. Geological Survey Open-File Report 00-92, 121 p.

Related Packages


Supported in


Other Notes

The SOR solver doesn't work well with the wetting capability.
If the Lake package is used, more iterations may be required.

Input Instructions

Input to the Slice-Successive Overrelaxation (SOR) Package is read from the file that is type "SOR" in the name file. All numeric variables are free format if the option “FREE” is specified in the Basic Package input file; otherwise, all the variables have 10-character fields.


Data Set 0


Item 0 is optional—“#” must be in column 1. Item 0 can be repeated multiple times.

Text—is a character variable (199 characters) that starts in column 2. Any characters can be included in Text. The “#” character must be in column 1. Except for the name file, lines beginning with # are restricted to these first lines of the file. Text is printed when the file is read.

Data Set 1

MXITER—is the maximum number of iterations allowed in a time step.

Data Set 2


ACCL—is the acceleration variable, usually between 1.0 and 2.0.

HCLOSE—is the head change criterion for convergence. When the maximum absolute value of head change from all nodes during an iteration is less than or equal to HCLOSE, iteration stops.

IPRSOR—is the printout interval for SOR. IF IPRSOR is equal to zero, it is changed to 999. The maximum head change (positive or negative) is printed for each iteration of a time step whenever the time step is an even multiple of IPRSOR. This printout also occurs at the end of each stress period regardless of the value of IPRSOR.