GROUND WATER -- Distribution of Open-File Report 92-477, "Documentation of a Computer Program to Simulate Horizontal-Flow Barriers Using the U.S. Geological Survey's Modular Three-DimensionalFinite-Difference Ground-Water Flow Model" by Paul A. Hsieh and John R. Freckleton


In Reply Refer To:                          January 10, 1994
Mail Stop 411


OFFICE OF GROUND WATER TECHNICAL MEMORANDUM 94.01

Subject:  GROUND WATER -- Distribution of Open-File
          Report 92-477, "Documentation of a Computer Program
          to Simulate Horizontal-Flow Barriers Using the
          U.S. Geological Survey's Modular Three-Dimensional
          Finite-Difference Ground-Water Flow Model" by
          Paul A. Hsieh and John R. Freckleton

The subject report describes the addition of the Horizontal Flow
Barrier (HFB) Package to the U.S. Geological Survey modular
model, MODFLOW.  The HFB Package makes it possible to easily
simulate low-permeability features that impede horizontal flow
of ground water such as vertical faults and slurry walls.  It is
possible to simulate such features without using the HFB Package
by using model cells with reduced hydraulic conductivity;
however, by using the HFB Package, the features can generally be
represented using a coarser grid, and the specification of input
data will be easier.  We recommend that this report be brought
to the attention of technical and management personnel concerned
with ground-water modeling studies.

A version of MODFLOW has been created that incorporates the HFB
Package along with most of the other published additions; this
version of MODFLOW will be distributed by the Hydrologic
Analysis Support Section on their next tape of computer
applications for the Data General computers.  Until that tape is
released, anyone in Water Resources Division can contact Steve
Regan by EDOC (RSREGAN) or phone (703 648-5896) to obtain the
updated version of MODFLOW.

Additional copies of the report are available from the authors.



                                  William M. Alley
                                  Chief, Office of
                                  Ground Water

Distribution:  A and B (memo only)
               S, FO, and PO (memo and report)