WATER, GROUND - Revised definitions.

                          GEOLOGICAL SURVEY
                      WATER RESOURCES DIVISION
                      WASHINGTON, D. C.  20242

In reply refer to:                            September 23, 1968
                                                       4037 0001


To:       Regional Hydrologists and District Chiefs, WRD

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

Subject:  WATER, GROUND - Revised definitions.

About three years ago the Chief Hydrologist appointed a Committee
on Redefinition of Hydrologic Terms under the chairmanship of
A. M. Piper (now, under S. W. Lohman).  The committee was formed
to deal with a number of ground-water terms that were giving
trouble in one way or another, and to date it has considered only
such terms.

The committee has not yet made a report, but it has reached
agreement on the first ten of a number of terms which are proposed
for revision.  Not all the definitions for even these ten have
been worked out completely, but it is appropriate to list the new
and superseded terms now because of various bibliographic and
indexing jobs which are in progress and in which it is desirable
that the new terms be used in place of the old.  Following are
the ten terms, their length-mass-time dimensions, as applicable,
and the terms that are replaced.

Term and symbol      Dimensions    units(1)       Term replaced

Hydraulic                                        Coefficient of
conductivity, K         ***see note               permeability

Transmissivity, T                                Coefficient of

permeability, k                                  No previous term

Storage              [Dimension-                 Coefficient of
coefficient, S         less]                        storage

Specific yield,  S(2)    [do.]

Potentiometric                                   Piezometric

Saturated zone                                   Zone of

Unsaturated zone                                 Zone of

Gaining stream                                   Effluent stream

Losing stream                                    Influent stream

The new terms may be used immediately in places where the general
concept rather than an exact definition is involved.  As soon as
possible, definitions will be completed and a list issued for
these ten, and additional ones if possible.

Adoption of consistent units for K and T in equations will
eliminate further use of conversion factors containing hidden
units, such as 527.7, 114.6, and 264.  Instead, such equations
will contain only the pure, dimensionless numbers that results
from their mathematical derivation, such as 2, 4, [**see
original], 2.30, and 0.577216.
(1) For comparison or machine handling of data. For other
    purposes, other units may be used as appropriate.

(2) To avoid confusion, the symbol for specific yield may be
    differentiated from that for storage coefficient by some
    means; a decision has not yet been reached.

***Please see original memorandum for equation information.

The committee report will of course, explain the reasoning behind
changes in terminology.  Copies of the committee report will be
distributed to recipients of this preliminary release.

                                   (s) C. L. McGuinness

WRD Distribution:  A, B, S, FO, PO