UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY WATER RESOURCES DIVISION WASHINGTON, D. C. 20242 In reply refer to: September 23, 1968 4037 0001 GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 69.3 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 Not all the definitions for even these ten have been worked out completely, but it is appropriate to list the new and superseded terms now because of various bibliographic and indexing jobs which are in progress and in which it is desirable that the new terms be used in place of the old.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. Suggested standard Term and symbol Dimensions units(1) Term replaced Hydraulic Coefficient of conductivity, K ***see note permeability Transmissivity, T Coefficient of transmissibility Intrinsic permeability, k No previous term Storage [Dimension- Coefficient of coefficient, S less] storage Specific yield, S(2) [do.] Potentiometric Piezometric Saturated zone Zone of saturation Unsaturated zone Zone of saturation 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, POWATER, GROUND - Revised definitions.