year, rainfall--See year, climatic.
year, water--See year, climatic.
yield--(1) The quantity of water expressed either as a con-
tinuous rate of flow (cubic feet per second, etc.) or as
a volume per unit of time (acre-feet per year, etc.)
which can be collected for a given use, or uses, from
surface or ground-water sources on a watershed. The
yield may vary with the use proposed, with the plan
of development, and also with economic considerations.
The term is more or less synonymous with water
crop. (2) Total runoff. (3) The stream flow in a given
interval of time derived from aunit area or watershed.
It is usually expressed in cubic feet per second per
square mile, determined by dividing the observed
stream flow at a given location by the drainage area
above that location. (4) To give way.
yield, dependable, n-years--The minimum supply of a
given water development that is available on demand,
with the understanding that lower yields will occur
once in n years, on the average.
yield, ground-water, economic--The maximum rate at
which water can be artificially withdrawn from an
aquifer throughout the foreseeable future without
depleting the supply or altering the chemical charac-
ter of the water to such an extent that withdrawal at
this rate is no longer economically possible. The
economic yield varies with economic conditions and
other factors such as recharge, natural discharge,
pumping head, etc. The term may be applied with re-
spect to the economic feasibility of withdrawal from
the standpoint only of those who artificially withdraw
water or from the standpoint of the economy of a river
valley or other larger area to which the aquifer con-
yield, ground-water, potential--The greatest rate of arti-
ficial withdrawal from an aquifer which can be
maintained throughout the foreseeable future without
regard to cost of recovery. The physical yield limit is,
therefore, equal to the present recharge, or that
anticipated in the foreseeable future, less the recover-
able natural discharge.
yield, safe--The maximum dependable draft which can be
1---------- 111-~ 1- 1 I III -
made continuously upon a source of water supply
(surface or ground water) during a period of years
during which the probable driest period or period of
greatest deficiency in water supply is likely to occur.
Dependability is relative and is a function of storage
provided and drought probability.
yield, specific--The quantity of water that a unit volume
of permeable rock or soil, after being saturated, will
yield when drained by gravity. It may be expressed as
a ratio or as a percentage by volume. The sum of
specific retention and specific yield equals the porosity
of the material drained.
yield, water--The total outflow from a drainage basin
through either surface channels or subsurface
yield, well, specific--See capacity, well.
young--Being in the stage of increasing vigor and efficiency
of action; said of some streams; also, being in the
stage of accentuation of and a tendency toward com-
plexity of form; said of some topography resulting
from land sculpture. Contrasted with mature and old.
zeolite--A chemical compound so imperfectly bound to-
Sgether that its composition will change in accordance
with the concentration of chemicals in solution in its
presence. Zeolites are used in water-softening
zero, absolute--That point on the absolute temperature
scale at which the linear velocities of the random
molecular motions of an ideal gas become zero,
i. e., at which the molecules are at rest. This occurs,
according to recent experimental determinations, at
-273.18 degrees C 0.03 degrees Cor-461 degrees F.
zone--In geology, used in the same sense as horizon to
indicate a certain geological level or chronological
position, without reference to the local attitude or dip
of the rock.
zone, aeration--That portion of the lithosphere in which the
functional interstices of permeable rock or earth are
not (except temporarily) filled with water under hydro-
static pressure; that is, the interstices either are not