EQUIPMENT AND SUPPLIES - Electric analog plotter

                           UNITED STATES
                    DEPARTMENT OF THE INTERIOR
                         GEOLOGICAL SURVEY
                     Water Resources Division
                        Washington 25, D.C.

In reply refer to:                                August 1, 1958
                                                  Code 4052 0001


To:       District Chiefs and staff Officials (GW)

From:     Chief, Ground Water Branch, Washington, D.C.

Subject:  EQUIPMENT AND SUPPLIES - Electric analog plotter

Because of the value of analog methods for analyzing some ground-
water flow problems a few field offices have purchased an electric
analog field plotter, initially made and sold by the General
Electric Company but now sold by the Sunshine Scientific
Instrument Company, 1810 Grant Avenue, Philadelphia 15,
Pennsylvania.  The price of the plotter is $265.

This plotter, which determines lines of equal potential or voltage
on a semi-conductive paper, has proved to be very useful in
studying steady-state flow problems in 2 dimensional system having
irregular or complex boundaries.  It is simple to operate and in
addition to its use in solving problems it provides an excellent
means of obtaining an understanding of flow nets.

The above plotter presumably was designed for general use (i.e.
problems in optics, heat flow, electricity, etc.) and accordingly
has some limitations when applied to ground-water problems.  One
of the chief limitations, so far as its use in ground-water
studies is concerned, is the inconvenient method of establishing
voltage or current differences (simulating differences in head and
discharge or recharge) required in many problems.

In order to have a similar unit but better suited to studying
ground-water problems a plotter was designed and constructed by
the Research Section of the Ground Water Branch as a part of the
Branch's analog research project.  This plotter contains twelve
adjustable current or voltage sources, a fixed voltage source, and
a ground.  Current in or out of these sources can be conveniently
measured by depressing a switch and reading a meter.  The meter
serves also as a null-point indicator for determining potentials.
The unit, which is contained in a metal box 8 x by 8 by 16 inches,
also includes the necessary power supplies and voltage and current
measuring circuits.

The following are a few examples of the types of problems in which
the analog field plotter is useful.

     1.  Aquifers having irregular external boundaries (area
     2.  Partially-penetrating wells.
     3.  Aquifers containing lenticular impervious beds.
     4.  Flow from stream to a well.
     5.  Effect of faults, dikes, and other partial barriers.
     6.  Problems involving the image theory.
     7.  Salt-fresh water interface position under static
     8.  Water-table profile near discharging well or drainage
     9.  Aquifer intersected by non-parallel or parallel streams.
    10.  Effect on flow patterns of artificial discharge or
         recharge on regional hydraulic gradient.
    11.  Refraction of stream lines and piezometric contours in
         anisotropic aquifers.
    12.  Flow patterns around radial collector wells and
         infiltration galleries.
    13.  Subsurface flow patterns around dams.
    14.  Flow patterns adjacent to lakes.
    15.  Velocity distribution in aquifers.
    16.  Effect of nonhomogeneity.
    17.  Flow from ditches and canals of various shaped cross

Inasmuch as this plotter seems to be well suited for use in many
ground-water studies it has been suggested that the Branch field
offices might be interested in having one or more available for
their personnel.  Thus the purpose of this memorandum is to
determine how many of the specially designed units would the field
offices purchase if they were available.

If the indicated demand is twenty or more it is likely they can be
constructed by a private contractor at a cost of about $300 each.

Would you please complete the attached form and return it to this
office (Code 4052 0001).  If it turns out that the cost will
substantially exceed $300 you will be so advised and you can then
cancel or reconfirm your purchase request.

Although the analog plotter is simple in principle and easy to
operate, an operational manual would be furnished with each unit.

                              (s) A. N. Sayre


Distribution:  A, B, S 3, FO 3