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OCR for page 113
APPEND 8 A
Glossary
alluvial Pertaining to processes or materials
associated with transportation or deposition by
running water.
aguiclude A formation that may contain ground
water but is incapable of transmitting it in
significant quantities. Aquicludes often form
confining layers for aquifers.
aquifer A sufficiently permeable formation
storing, transmitting, and yielding ground water
in useable quantities.
aquitard A layer of low permeability that may
contain and transmit water from one aquifer to
another but cannot itself serve as an aquifer.
An aquitard is a leaky, semiconfining layer.
argillaceous Containing appreciable clay.
artesian aquifer See confined aquifer.
bulk density The weight of a dry porous medium
per unit volume of the material in its natural
conditions (including pores and voids).
calcareous Containing sufficient free carbonate
to effervesce visibly when treated with cold 0.1
M HC1.
carbonaceous Pertaining to, or rich in, carbon.
elastic Consisting of fragments of rocks or of
organic structures that have been moved
individually from their places of origin.
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coastal plain Any plain that has its margin on
the shore of a large body of water, particularly
the sea.
colluvium A general term applied to deposits on
a slope or at the foot of a sloppier cliff that
were moved there chiefly by gravity.
confined aquifer An aquifer with an upper
boundary that is a confining layer and having a
pressure potential at this boundary in excess of
atmospheric. The potentiometric surface of a
confined aquifer is above the top of the
aquifer. Also known as an artesian aquifer.
confining layer A layer of material having a
permeability lower than that of the associated
aquifer. If the permeability is essentially
zero, the confining layer is impermeable and may
be an aquifuge or an aquiclude. If the
permeability is small relative to that of the
adjoining aquifer, the layer is said to be leaky
and is called an aquitard.
Darcy's equation A formula stating that the flow
rate of water through a porous medium is
proportional to the hydraulic gradient. The
factor of proportionality is the hydraulic
conductivity.
fluvial Of, or pertaining to, rivers; produced
by river action. ,
fracture A crack in a rock formation usually
formed by stresses imposed on or released from
the formation. Fractures may be interconnected
or isolated.
fragipan A natural subsurface soil horizon with
high bulk density and/or high mechanical strength
relative to the soil horizons above, seemingly
cemented when dry, but when moist showing a
moderate to weak brittleness.
ground water Subsurface water under a pressure
greater than atmospheric.
hysteretic function The difference between water
content and water pressure relations in
unsaturated porous media due to antecedent
conditions, i.e., wetting or drying.
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hydraulic conductivity The factor of
proportionality in Darcy's equation relating flow
velocity to hydraulic gradient having units of
length per unit of time. A property of the
porous medium and the water content of the
medium. ,
hydraulic head The energy per unit weight of
water made up of the sum of the pressure
potential (head), velocity potential (head), and
elevation potential (head). The velocity head is
often negligible and taken as zero for subsurface
flow. Also called water potential.
illuvial (clay) Clay that has moved into a soil
horizon from the soil horizons above.
intrinsic permeability A quantitative measure of
water-transmitting ability of a porous medium
that is related to the size and
interconnectedness of the void openings.
lenticular Shaped approximately like a double
convex lens.
Ethology The physical character of a rock,
generally as determined megascopically or with
the aid of a low-power magnifier.
loess A sediment, commonly nonstratified and
commonly unconsolidated, composed dominantly of
silt-size particles, ordinarily with accessory
clay and sand, deposited primarily by the wind.
perched aquifer A localized unconfined aquifer
formed above a relatively impermeable layer. May
be seasonal due to recharge patterns and leakage
through and flow around the restricting layer.
permeability A description of the ease with
which a fluid may move through a porous medium;
abbreviation of intrinsic permeability.
phreatic surface Same as water table.
piezometric surface The surface defined by a
pressure potential and position. For an
unconfined aquifer it is equal to the elevation
of the water table. For a confined aquifer it is
equal to the elevation to which water would rise
in a well penetrating and open to the aquifer.
porosity A measure of the total void space
present in a volume of formation. The percentage
of any volume of material occupied by voids.
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Voids may be filled with water or air. If all of
the voids are filled with water, saturation
exists. Porosity consists of primary and
secondary porosity.
potential gradient or hydraulic gradient The
change in hydraulic head per unit distance.
primary porosity Porosity composed of voids
between individual particles such as grains of
sand and gravel or clay or silt particles.
residuum Unconsolidated and partly weathered
mineral materials accumulated by disintegration
of consolidated rock in place.
saline (soil) A soil containing sufficient
soluble salt to adversely affect the growth of
most crop plants.
saturation The condition that exists when all
voids are filled with water.
secondary porosity Porosity due to fractures,
solution channels, root channels, and animal
burrows.
sodic (soils A nonsaline soil containing
sufficient exchangeable sodium to adversely
affect crop production and soil structure under
most soil and plant type conditions.
solution channels Channels formed within soluble
rocks (such as limestones by the action of water
and chemicals in dissolving rock material.
specific capacity The Yield of a well per unit
crop or the water ~eve' In the we'' (volume per
unit time per unit lengthy.
~ ~ ,
specific retention The volume of water retained
per unit volume of material when the material is
allowed to drain due to gravity. Similar to
field capacity in an agricultural setting.
Specific retention plus specific yield equals
porosity.
specific Yield The volume of water drained per
material is
Specific yield
_ the same for an
unconfined aquifer. Specific yield plus specific
retention equals porosity.
unit volume of material when the
allowed to drain due to gravity
and the storage coefficient are
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storage coefficient The volume of water released
per unit area of aquifer and per unit drop in
head.
till (glacial) Nonsorted, nonstratified sediment
carried or deposited by a glacier.
unconfined aquifer An aquifer with a water table
as an upper surface. Also known as a water table
aqua: :er.
vadose zone The zone between the surface and the
aquifer containing water at pressures less than
atmospheric. It includes the capillary fringe.
water table The surface defining the location
where the pressure potential is atmospheric for
an unconfined aquifer. Equivalent to the
phreatic surface. The water table is the top of
an unconfined aquifer
.
Representative terms from entire chapter:
unconfined aquifer
