PUBLICATIONS--Release of reports, "A modular finite- element model (MODFE) for areal and axisymmetric ground-water flow problems,"


In Reply Refer To:                             January 4, 1992
Mail Stop 411


OFFICE OF GROUND WATER TECHNICAL MEMORANDUM NO. 93.02

Subject:  PUBLICATIONS--Release of reports, "A modular finite-
          element model (MODFE) for areal and axisymmetric
          ground-water flow problems,"

          Part 1:  Model description and user's manual, Open-File
                   Report 90-194, by Lynn J. Torak;

          Part 2:  Derivation of finite-element equations and
                   comparisons with analytical solutions,
                   Techniques of Water-Resources Investigations
                   (TWRI), Book 6, Chapter A4, by Richard L.
                   Cooley;

          Part 3:  Design philosophy and programming details,
                   Open-File Report 91-471, by Lynn J. Torak.

The subject reports (attached) document a new program, MODFE, a
MODular Finite Element model for simulating steady- or unsteady-
state, areal and axisymmetric flow of ground water in a
heterogeneous anisotropic aquifer.  Parts 1 and 3 are being
processed to be published in the future as TWRI's.

Physical processes that can be represented by MODFE include
(1) confined flow, unconfined flow (using the Dupuit
approximation), or a combination of both; (2) leakage through
either rigid or elastic confining units (the latter case gives
rise to what is referred to as transient leakage); (3) specified
recharge or discharge at points, along lines, or areally; (4) flow
across specified-flow, specified-head, or head-dependent
boundaries; (5) decrease of aquifer thickness to zero under
extreme water-table decline and increase of aquifer thickness
from zero as the water table rises; and (6) head-dependent fluxes
from springs, drainage wells, leakage across riverbeds or
confining units combined with aquifer dewatering, and
evapotranspiration.

The finite-element method involves subdividing the two-
dimensional spatial region into a network of subregions, called
elements.  The spatial element shapes used in this model are
triangles and the elements are assumed to have been selected small
enough that at any instant of time the true variation of head
within each element is approximately linear.

The source code for MODFE can be obtained from the hydrologic
applications tape that was distributed to all WRD computer site
managers this past summer.  This tape was created by the
Hydrologic Analysis Support Section (HASS).  If you cannot locate
this tape or have questions about its contents, contact Alan Lumb
(EDOC AMLUMB), Kate Flynn (EDOC KMFLYNN), or Steven Regan (EDOC
RSREGAN).

We recommend that these reports be brought to the attention of
technical and management personnel concerned with ground-water
modeling studies.




                          Acting Chief, Office
                            of Ground Water

Attachments

Distribution:  A and B (memo only)
               S (NR (20), CR (35), WR (5)), FO, and PO
               (memo and reports)