GEOLOGICAL SURVEY
                      RESTON, VIRGINIA  22092

                                                  June 23, 1977


Subject:   PUBLICATIONS--Report, "Simulation procedure for
                         modeling transient water-table and
                         artesian stress and response," by
                         J. E. Reed, M. S. Bedinger, and
                         J. E. Terry.

The subject report, published as U.S. Geological Survey open-file
report 76-792, describes a computer program, SUPERMOCK, that was
developed to model a ground-water system affected by surface
hydrology; i.e., stream stage, evapotranspiration, etc.  The
prototype flow system is an alluvial aquifer overlain by a
relatively thin confining bed.

The model consists of three components--a soil-moisture accounting
component, a vertical flow component, and a horizontal ground-
water flow component.  The soil-moisture accounting component is a
parametric rainfall-accretion model that is used to compute
changes in soil-moisture storage, and recharge and discharge from
the zone of aeration to the water table.  Infiltration to soil
moisture is computed as a function of precipitation in excess of
evapotranspiration, the amount of soil moisture already in
storage, and parameters describing the hydraulic properties of the

The vertical-flow component is used to compute the altitude of the
water table in the fine-grained material above the aquifer.
Water-table altitude is computed as a function of transient flow
through the fine-grained material above the aquifer and transient
altitude of head in the aquifer.

The horizontal-flow component computes accretion to the aquifer
and the transient altitude of the potentiometric surface in the
aquifer.  Stresses simulated on the aquifer include changes in
stream stage, withdrawal by wells, and accretion (infiltration and
evapotranspiration through the fine-grained material above the

The level of discretization can be different in the three
components of SUPERMOCK.  Generally, parameters are constant over
the modeled area in the soil-moisture accounting component.  The
exceptions to this are root depth, which varies from node to node,
and the hydraulic conductivity from the base of the root zone down
to the water table, which is constant over user-defined areas.  In
the vertical-flow component, parameters are discretized as
constant over user-specified areas.  In the horizontal-flow
component, parameters can be discretized node by node.  However,
the results of the interaction of model parameters and model
stress in the three components--soil moisture storage, water-table
head, and potentiometric head--all vary from node to node.

The approaches used in SUPERMOCK should be of interest to others
concerned with modeling ground-water systems.  Please bring this
report to the attention of personnel concerned with modeling
ground-water systems.  Additional copies of the report are
available on request.

                              (s) Charles A. Appel
                              Charles A. Appel
                              (for) Chief, Ground Water Branch
                              Water Resources Division

WRD Distribution:   A (w/o attach.), B (limited), FO-LS, SL
(Subdistrict Offices, w/o
attach.), S (w/o attach.)