is a definition of terms frequently used in the instrumentation, industrial
automation and test & measurement communities. Click on the first
letter of the term you wish to look up.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
- abandoned water right
- a water right which was not put to beneficial
use for a number of years, generally five to seven years.
- abandoned well
- a well which is no longer used. In many
places, abandoned wells must be filled with cement or concrete grout
to prevent pollution of ground water bodies.
- to take in.
- a gradual increase in land area adjacent
to a river.
- acid rain
- the acidic rainfall which results when
rain combines with sulfur oxides emissions from combustion of fossil
- the amount of water required to cover
one acre to a depth of one foot. An acre-foot equals 325,851 gallons,
or 43,560 cubic feet. A flow of 1 cubic feet per second produce 1.98 acre-feet per day.
- activated carbon adsorption
- the process of pollutants moving out of
water and attaching on to activated carbon.
- the molecular attraction asserted between
the surfaces of bodies in contact. Compare cohesion.
- a court proceeding to determine all rights
to the use of water on a particular stream system or ground water basin.
- the adhesion of a substance to the surface
of a solid or liquid. Adsorption is often used to extract pollutants
by causing them to be attached to such adsorbents as activated carbon
or silica gel. Hydrophobic, or water-repulsing adsorbents, are used
to extract oil from waterways in oil spills.
- the mixing or turbulent exposure of water
to air and oxgen to dissipate volatile contaminants and other pollutants
into the air.
- aggressive water
- water which is soft and acidic and can
corrode plumbing, piping, and appliances.
- the measurement of constituents in a water
supply which determine alkaline conditions. The alkalinity of water
is a measure of its capacity to neutralize acids. See pH.
- algal bloom
- a phenomenon whereby excessive nutrients
within a river, stream or lake cause an explosion of plant life which
results in the depletion of the oxygen in the water needed by fish and
other aquatic life. Algae bloom is usually the result of urban runoff
(of lawn fertilizers, etc.). The potential tragedy is that of a "fish
kill," where the stream life dies in one mass extinction.
- sediments deposited by erosional processes,
usually by streams.
- a sudden or perceptible change in a river's
margin, such as a change in course or loss of banks due to flooding.
- annular space
- the space between two concentric cylindrical
objects, one of which surrounds the other, such as the space between
the walls of a drilled hole and a casing.
- growing in, living in, or frequenting
- a formation which, although porous and
capable of absorbing water slowly, will not transmit water fast enough
to furnish an appreciable supply for a well or a spring.
- sediments deposited by erosional processes,
usually by streams .
- the raising or fattening of fish in enclosed
ponds. Compare mariculture.
- a geologic formation that will yield water
to a well in sufficient quantities to make the production of water from
this formation feasible for beneficial use; permeable layers of underground
rock or sand that hold or transmit groundwater below the water table.
- a geologic formation in which water is
under sufficient hydrostatic pressure to be discharged to the surface
- artesian well
- a water well drilled into a confined aquifer
where enough hydraulic pressure exists for the water to flow to the
surface without pumping.
- artesian zone
- a zone where water is confined in an aquifer
under pressure so that the water will rise in the well casing or drilled
hole above the bottom of the confining layer overlying the aquifer.
- average annual
- amount of water entering the aquifer on
an average annual basis. Averages mean very little for the Edwards because
the climate of the region and structure of the aquifer produce a situation
in which the area is usually water rich or water poor.
- reverse seepage of water in a distribution
- reversing the flow of water through a
home treatment device filter or membrane to clean and remove deposits.
- any artificial obstruction placed in water
to increase water level or divert it. Usually the idea is to control
peak flow for later release.
- the amount of water necessary when reasonable
intelligence and diligence are used for a stated purpose; Texas law
recognizes the following uses as beneficial: (1) domestic and municipal
uses, (2) industrial uses, (3) irrigation, (4) mining, (5) hydroelectric
power, (6) navigation, (7) recreation, (8) stock raising, (9) public
parks, and (10) game preserves.
- uptake and retention of substances by
an organism from its surrounding medium (usually water) and from food.
- a test used to evaluate the relative potency
of a chemical by comparing its effect on a living organism with the
effect of a standard population on the same type of organism.
- a process that uses living organisms to
- a nutrient-rich organic material resulting
from the treatment of wastewater. Biosolids contain nitrogen and phosphorus
along with other supplementary nutrients in smaller doses, such as potassium,
sulfur, magnesium, calcium, copper and zinc. Soil that is lacking in
these substances can be reclaimed with biosolids use. The application
of biosolids to land improves soil properties and plant productivity,
and reduces dependence on inorganic fertilizers.
- the earth and all its ecosystems
- wastewater from toilet, latrine, and agua
privy flushing and sinks used for food preparation or disposal of chemical
or chemical-biological ingredients.
- water samples containing a chemical of
known concentration given a fictitious company name and slipped into
the sample flow of the lab to test the impartiality of the lab staff.
- the water drawn from boiler systems and
cold water basins of cooling towers to prevent the buildup of solids.
- a type of wetland that accumulates appreciable
peat deposits. They depend primarily on precipitation for their water
source, and are usually acidic and rich in plant matter with a conspicuous
mat or living green moss.
- boiling point
- the temperature at which a liquid boils.
It is the temperature at which the vapor pressure of a liquid equals
the pressure on its surface. If the pressure of the liquid varies, the
actual boiling point varies. For water it is 212 degrees Fahrenheit
or 100 degrees Celsius.
- Biochemical Oxygen Demand. A measure of
the amount of oxygen required to neutralize organic wastes.
- highly salty and heavily mineralized water
containing heavy metal and organic contaminants.
- the tendency of a body to float or rise
when immersed in a fluid; the power of a fluid to exert an upward force
on a body placed in it.
- CACO3 - a white precipitate that forms
in water lines, water heaters and boilers in hard water areas; also
known as scale.
- amount of energy required to raise the
temperature of 1 gram of water 1 degree Celsius.
- capillary zone
- soil area above the water table where
water can rise up slightly through the cohesive force of capillary action.
- a class of new-age pesticides that attack
the nervous system of organisms.
- the collective term for the natural inorganic
chemical compounds related to carbon dioxide that exist in natural waterways.
- a tubular structure intended to be watertight
installed in the excavated or drilled hole to maintain the well opening
and, along with cementing, to confine the ground waters to their zones
of origin and prevent the entrance of surface pollutants.
- a large underground opening in rock (usually
limestone) which occurred when some of the rock was dissolved by water.
In some igneous rocks, caverns can be formed by large gas bubbles.
- cement grout
- a mixture of water and cement in the ratio
of not more than 5-6 gallons of water to a 94 pound sack of portland
cement which is fluid enough to be pumped through a small diameter pipe.
- Comprehensive Environment Response, Compensation
and Liability Act. Also known as SUPERFUND. The Act gave EPA the authority
to clean up abandoned, leaky hazardous waste sites.
- certificate of water right
- an official document which serves as court
evidence of a perfected water right.
- colony forming units.
- check dam
- a small dam constructed in a gully or
other small water course to decrease the streamflow velocity, minimize
channel erosion, promote deposition of sediment and to divert water
from a channel.
- attack and dissolving of parent rock by
exposure to rainwater, surface water, oxygen, and other gases in the
atmosphere, and compounds secreted by organisms. Contrast physical
- the adding of chlorine to water or sewage
for the purpose of disinfection or other biological or chemical results.
- chlorine demand
- the difference between the amount of chlorine
added to water, sewage, or industrial wastes and the amount of residual
chlorine remaining at the end of a specific contact period. Compare residual chlorine.
- chute spillway
- the overall structure which allows water
to drop rapidly through an open channel without causing erosion. Usually
constructed near the edge of dams.
- to move in a circle, circuit or orbit;
to flow without obstruction; to follow a course that returns to the
- a tank used to collect rainwater runoff
from the roof of a house or building.
- climatic cycle
- the periodic changes climate displays,
such as a series of dry years following a series of years with heavy
- climatic year
- a period used in meteorological measurements.
The climatic year in the U.S. begins on October 1.
- generalized weather at a given place on
earth over a fairly long period; a long term average of weather. Compare weather.
- a torrential downpour of rain, which by
it spottiness and relatively high intensity suggests the bursting and
discharge of water from a cloud all at once.
- in water treatment, the use of chemicals
to make suspended solids gather or group together into small flocs.
- a molecular attraction by which the particles
of a body are united throughout the mass whether like or unlike. Compare adhesion.
- cold vapor
- method to test water for the presence
- coliform bacteria
- non-pathogenic microorganisms used in
testing water to indicate the presence of pathogenic bacteria.
- collector well
- a well located near a surface water supply
used to lower the water table and thereby induce infiltration of surface
water through the bed of the water body to the well..
- finely divided solids which will not settle
but which may be removed by coagulation or biochemical action.
- combined sewer
- a sewer system that carries both sanitary
sewage and stormwater runoff. When sewers are constructed this way,
wastewater treatment plants have to be sized to deal with stormwater
flows and oftentimes some of the water receives little or no treatment.
Compare separate sewer.
- sealing off access of undesireable water
to the well bore by proper casing and/or cementing procedures.
- a sample composed of two or more portions
collected at specific times and added together in volumes related to
the flow at time of collection. Compare grab sample.
- amount of a chemical or pollutant in a
particular volume or weight of air, water, soil, or other medium.
- the change of state from a gas to a liquid.
Compare evaporation, sublimation.
- a natural or artificial channel through
which fluids may be conveyed.
- cone of depression
- natural depression in the water table
around a well during pumping.
- confined aquifer
- an aquifer that lies between two relatively
impermeable rock layers.
- confining bed
- a body of impermeable or distinctly less
permeable material stratigraphically adjacent to one or more aquifers.
- confluent growth
- in coliform testing, abundant or overflowing
bacterial growth which makes accurate measurement difficult or impossible.
- conjunctive management
- integrated management and use of two or
more water resources, such as an aquifer and a surface water body.
- connate growth
- water trapped in the pore spaces of a
sedimentary rock at the time it was deposited. It is usually highly
- to protect from loss and waste. Conservation
of water may mean to save or store water for later use.
- consolidated formation
- naturally occurring geologic formations
that have been lithified (turned to stone). The term is sometimes used
interchangeably with the term "bedrock." Commonly, these formations
will stand at the edges of a bore hole without caving.
- consumptive use
- the quantity of water not available for
reuse. Evapotranspiration, evaporation, incorporation into plant tissue,
and infiltration into groundwater are some of the reasons water may
not be available for reuse. Compare nonconsumptive
- contact recreation
- activities involving a significant risk
of ingestion of water, such as wading by children, swimming, water skiing,
diving and surfing. Compare noncontact recreation..
- the introduction into water of sewage
or other foreign matter that will render the water unfit for its intended
- cooling tower
- large tower used to transfer the heat
in cooling water from a power or industrial plant to the atmosphere
either by direct evaporation or by convection and conduction.
- correlative rights
- rights that are coequal or that relate
to one another, so that any one owner cannot take more than his share.
- a small stream of water which serves as
the natural drainage course for a drainage basin. The term is relative
according to size. Some creeks in a humid region would be called rivers
if they occurred in an arid area.
- the top of a dam, dike, or spillway, which
water must reach before passing over the structure; the summit or highest
point of a wave; the highest elevation reached by flood waters flowing
in a channel.
- critical low flow
- low flow conditions below which some standards
do not apply. The impacts of permitted discharges are analyzed at critical
- cubic foot per second
- the rate of discharge representing a volume
of one cubic foot passing a given point during 1 second. This rate is
equivalent to approximately 7.48 gallons per second, or 1.98 acre-feet per day.
- the portion of a stream or body of water
which is moving with a velocity much greater than the average of the
rest of the water. The progress of the water is principally concentrated
in the current. See thalweg.
- a structure of earth, rock, or concrete
designed to form a basin and hold water back to make a pond, lake, or
- deionized water
- water free of inorganic chemicals.
- an alluvial deposit made of rock particles
(sediment, and debris) dropped by a stream as it enters a body of water.
- the number of units of something that
will be purchased at various prices at a point in time. Compare supply.
- dental fluorosis
- disorder caused by excessive absorption
of fluorine and characterized by brown staining of teeth.
- something dropped or left behind by moving
water, as sand or mud.
- the process of salt removal from sea or
- detection limit
- the lowest level that can be determined
by a specific analytical procedure or test method.
- consisting of or abounding in diatoms,
a class of unicellular or colonial algae having a silicified cell wall
that persists as a skeleton after death.
- diluting water
- distilled water that has been stabilized,
buffered, and aerated. Used in the BOD test.
- the volume of water that passes a given
point within a given period of time. It is an all-inclusive outflow
term, describing a variety of flows such as from a pipe to a stream,
or from a stream to a lake or ocean.
- discharge permit
- a permit issued by a state or the federal
government to discharge effluent into waters of the state or the United
States. In many states both State and federal permits are required.
- the killing of the larger portion of the
harmful and objectionable bacteria in the sewage. Usually accomplished
by introduction of chlorine, but more and more facilities are using
exposure to ultraviolet radiation, which renders the bacteria sterile.
- disinfection byproducts
- halogenated organic chemicals formed when
water is disinfected.
- the movement and spreading of contaminants
out and down in an aquifer.
- distance by which portions of the same
geological layer are offset from each other by a fault.
- the process by which solid particles mix
molecule by molecule with a liquid and appear to become part of the
- dissolved oxygen (DO)
- amount of oxygen gas dissolved in a given
quantity of water at a given temperature and atmospheric pressure. It
is usually expressed as a concentration in parts per million or as a
percentage of saturation.
- dissolved solids
- inorganic material contained in water
or wastes. Excessive dissolved solids make water unsuitable for drinking
or industrial uses. See TDS.
- water treatment method where water is
boiled to steam and condensd in a separate reservoir. Contaminants with
higher boiling points than water do not vaporize and remain in the boiling
- distilled water
- water that has been treated by boiling
and condensation to remove solids, inorganics, and some organic chemicals.
- to remove water from a water body. Diversions
may be used to protect bottomland from hillside runoff, divert water
away from active gullies, or protect buildings from runoff.
- drainage area
- of a stream at a specified location is
that area, measured in a horizontal plane, enclosed by a topographic
divide from which direct surface runoff from precipitation normally
drains by gravity into the stream above the specified location.
- driller's well log
- a log kept at the time of drilling showing
the depth, thickness, character of the different strata penetrated,
location of water-bearing strata, depth, size, and character of casing
- deposits of calcium carbonate that include
stalactites, stalagmites, columns, and cave pearls.
- although there is no universally accepted
definition of drought, it is generally the term applied to periods of
less than average precipitation over a certain period of time. In south
Texas ranchers say drought begins as soon as it stops raining.
- two separate samples with separate containers
taken at the same time at the same place.
- total of all the ecosystems on the planet,
along with their interactions; the sphere of air, water, and land in
which all life is found.
- Edwards Aquifer
- an arch-shaped belt of porous, water bearing
limestones composed of the Comanche Peak, Edwards, and Georgetown formations
trending from west to east to northeast through Kinney, Uvalde, Medina,
Bexar, Comal, Hays, Travis, and Williamson counties.
- Edwards outcrop
- where the Edwards and associated limestone
formations are found at the surface. This area is also referred to as
the Recharge Zone.
- effective porosity
- the portion of pore space in saturated
permeable material where the movement of water takes place.
- effective precipitation
- the part of precipitation which produces
runoff; a weighted average of current and antecedent precipitation "effective"
in correlating with runoff. It is also that part of the precipitation
falling on an irrigated area which is effective in meeting the requirements
of consumptive use.
- any substance, particularly a liquid,
that enters the environment from a point source. Generally refers to
wastewater from a sewage treatment or industrial plant.
- a process which uses an electrical current
and an arrangement of permeable membranes to separate soluble minerals
from water. It is often used to desalinate salt or brackish water.
- one having so few individual survivors
that the species could soon become extinct in all or part of its region.
- enteric viruses
- a category of viruses related to human
excreta found in waterways.
- aggregate of external conditions that
influence the life of an individual organism or population.
- Environmental Protection Agency
- warm, less dense top layer in a stratified
lake. Compare hypolimnion.
- the wearing away of the land surface by
wind, water, ice or other geologic agents. Erosion occurs naturally
from weather or runoff but is often intensified by human land use practices.
- the topographic expression of a fault.
- estuarine waters
- deepwater tidal habitats and tidal wetlands
that are usually enclosed by land but have access to the ocean and are
at least occasionally diluted by freshwater runoff from the land (such
as bays, mouths of rivers, salt marshes, lagoons).
- estuarine zone
- area near the coastline that consists
of estuaries and coastal saltwater wetlands.
- thin zone along a coastline where freshwater
system(s) and river(s) meet and mix with a salty ocean (such as a bay,
mouth of a river, salt marsh, lagoon).
- euphotic zone
- surface layer of an ocean, lake, or other
body of water through which light can penetrate. Also known as the zone
- having a large or excessive supply of
plant nutrients (nitrates and phosphates). Compare oligotrophic.
- eutrophication (natural)
- an excess of plant nutrients from natural
erosion and runoff from the land in an aquatic ecosystem supporting
a large amount of aquatic life that can deplete the oxygen supply.
- the change by which any substance is converted
from a liquid state and carried of in vapor. Compare condensation, sublimation.
- combination of evaporation and transpiration
of water into the atmosphere from living plants and soil. Distinguish transpiration.
- external cost
- cost of production or consumption that
must be borne by society; not by the producer.
- complete disappearance of a species because
of failure to adapt to environmental change.
- fecal coliform
- the portion of the coliform bacteria group
which is present in the intestinal tracts and feces of warm-blooded
animals. A common pollutant in water.
- a type of wetland that accumulates peat
deposits, but not as much as a bog. Fens are less
acidic than bogs, deriving most of their water from groundwater rich
in calcium and magnesium.
- fermentation, anaerobic
- process in which carbohydrates are converted
in the absence of oxygen to hydrocarbons (such as methane).
- field capacity
- the amount of water held in soil against
the pull of gravity.
- a device used to remove solids from a
mixture or to separate materials. Materials are frequently separated
from water using filters.
- the mechanical process which removes particulate
matter by separating water from solid material, usually by passing it
- "first in time, first
- phrase indicating that older water rights
have priority over more recent rights if there is not enough water to
satisfy all rights.
- fixed ground water
- water held in saturated material that
it is not available as a source of water for pumping.
- large scale treatment process involving
gentle stirring whereby small particles in flocs are collected into
larger particles so their weight causes them to settle to the bottom
of the treatment tank.
- an overflow or inundation that comes from
a river or other body of water and causes or threatens damage. It can
be any relatively high streamflow overtopping the natural or artificial
banks in any reach of a stream. It is also a relatively high flow as
measured by either gage height or discharge quantity.
- land next to a river that becomes covered
by water when the river overflows its banks .
- plant population of a region.
- the rate of water discharged from a source
expressed in volume with respect to time.
- flow augmentation
- the addition of water to meet flow needs.
- the water behind a dam.
- forfeited water right
- a water right canceled because of several
consecutive years of nonuse.
- free ground water
- water in interconnected pore spaces in
the zone of saturation down to the first impervious barrier, moving
under the control of the water table slope.
- the change of a liquid into a solid as
temperature decreases. For water, the freezing point is 32 F or 0 C.
- fresh water
- water containing less than 1,000 parts
per million (ppm) of dissolved solids of any type. Compare saline
- fresh:salt water interface
- the region where fresh water and salt
water meet. In the Edwards region, it is commonly referred to as the
"bad water line", although it is zone and not a line.
- a covering of minute ice crystals on a
- gaging station
- the site on a stream, lake or canal where
hydrologic data is collected.
- A unit of volume. A U.S. gallon contains
231 cubic inches, 0.133 cubic feet, or 3.785 liters. One U.S. gallon
of water weighs 8.3 lbs.
- a term which denotes the branch of hydrology
relating to subsurface or subterranean waters; that is, to all waters
below the surface.
- geologic erosion
- normal or natural erosion caused by geological
processes acting over long geologic periods and resulting in the wearing
away of mountains, the building up of floodplains, coastal plains, etc.
- geopressured reservoir
- a geothermal reservoir consisting of porous
sands containing water or brine at high temperature or pressure.
- a periodic thermal spring that results
from the expansive force of super heated steam..
- a huge mass of land ice that consists
of recrystallized snow and moves slowly downslope or outward.
- grab sample
- a sample taken at a given place and time.
Compare composite sample.
- granular activated carbon
- pure carbon heated to promote "active"
sites which can adsorb pollutants. Used in some home water treatment
systems to remove certain organic chemicals and radon.
- wastewater from clothes washing machines,
showers, bathtubs, handwashing, lavatories and sinks that are not used
for disposal of chemical or chemical-biological ingredients.
- water within the earth that supplies wells
and springs; water in the zone of saturation where all openings in rocks
and soil are filled, the upper surface of which forms the water table.
- groundwater hydrology
- the branch of hydrology that deals with
groundwater; its occurrence and movements, its replenishment and depletion,
the properties of rocks that control groundwater movement and storage,
and the methods of investigation and utilization of ground water.
- groundwater law
- the common law doctrine of riparian rights
and the doctrine of prior appropriation as applied to ground water.
- groundwater recharge
- the inflow to a ground water reservoir.
- groundwater reservoir
- an aquifer or aquifer system in which
ground water is stored. The water may be placed in the aquifer by artificial
or natural means.
- groundwater runoff
- the portion of runoff which has passed
into the ground, has become ground water, and has been discharged into
a stream channel as spring or seepage water.
- groundwater storage
- the storage of water in groundwater reservoirs.
- a deeply eroded channel caused by the
concentrated flow of water.
- gully reclamation
- use of small dams of manure and straw;
earth, stone,or concrete to collect silt and gradually fill in channels
of eroded soil.
- a form of precipitation which forms into
balls or lumps of ice over 0.2 inch in diameter. Hail is formed by alternate
freezing and melting as precipitation is carried up and down in highly
turbulent air currents.
- a shallow layer of earth material which
has become relatively hard and impermeable, usually through the deposition
of minerals. In the Edwards region hardpans of clay are common.
- hard water
- water containing a high level of calcium,
magnesium, and other minerals. Hard water reduces the cleansing power
of soap and produces scale in hot water lines and appliances.
- hardness (water)
- condition caused by dissolved salts of
calcium, magnesium, and iron, such as bicarbonates, carbonates, sulfates,
- the pressure of a fluid owing to its elevation,
usually expressed in feet of head or in pounds per square inch, since
a measure of fluid pressure is the height of a fluid column above a
given or known point.
- the gate that controls water flow into
irrigation canals and ditches. A watermaster regulates the headgates
during water distribution and posts headgate notices declaring official
- heat of vaporization
- the amount of heat necessary to convert
a liquid (water) into vapor.
- heavy water
- water in which all the hydrogen atoms
have been replaced by deuterium.
- holding pond
- a small basin or pond designed to hold
sediment laden or contaminated water until it can be treated to meet
water quality standards or be used in some other way.
- hydroelectric plant
- electric power plant in which the energy
of falling water is used to spin a turbine generator to produce electricity.
- a chart that measures the amount of water
flowing past a point as a function of time.
- hydrologic cycle
- natural pathway water follows as it changes
between liquid, solid, and gaseous states; biogeochemical cycle that
moves and recycles water in various forms through the ecosphere. Also
called the water cycle.
- hydrologic unit
- is a geographic area representing part
or all of a surface drainage basin or distinct hydrologic feature.
- an instrument used to measure the density
of a liquid.
- electrical energy produced by falling
- hygroscopic nuclei
- piece of dust or other particle around
which water condenses in the atmophere. These tiny droplets then collide
and coalesce, with as many as 10,000 nuclei contributing to formation
of a raindrop.
- region that includes all the earth's liquid
water, frozen water, floating ice, frozen upper layer of soil, and the
small amounts of water vapor in the Earth's atmosphere.
- hydrostatic head
- a measure of pressure at a given point
in a liquid in terms of the vertical height of a column of the same
liquid which would produce the same pressure.
- hydrostatic pressure
- pressure exerted by or existing within
a liquid at rest with respect to adjacent bodies.
- bottom layer of cold water in a lake.
- a solid form of water.
- material that does not permit fluids to
- the quality or state of being impermeable;
resisting penetration by water or plant roots. Impervious ground cover
like concrete and asphalt affects quantity and quality of runoff.
- a body of water such as a pond, confined
by a dam, dike, floodgate or other barrier. It is used to collect and
store water for future use.
- inchoate water right
- an unperfected water right.
- indicator organisms
- microorganisms, such as coliforms, whose
presence is indicative of pollution or of more harmful microorganism.
- indicator tests
- tests for a specific contaminant, group
of contaminants, or constituent which signals the presence of something
else (ex., coliforms indicate the presence of pathogenic bacteria).
- inland freshwater wetlands
- swamps, marshes, and bogs found inland
beyond the coastal saltwater wetlands.
- instream use
- use of water that does not require withdrawal
or diversion from its natural watercourse; for example, the use of water
for navigation, recreation, and support of fish and wildlife.
- interbasin transfer
- the physical transfer of water from one
watershed to another; regulated by the Texas Water Code.
- one that flows periodically. Compare perennial stream.
- interstate water
- according to law, interstate waters are
defined as (1) rivers, lakes and other waters that flow across or form
a part of state or international boundaries; (2) waters of the Great
Lakes; (3) coastal waters whose scope has been defined to include ocean
waters seaward to the territorial limits and waters along the coastline
(including inland streams) influenced by the tide.
- the void or empty portion of rock or soil
occupied by air or water.
- irrigation efficiency
- the percentage of water applied, and which
can be accounted for, in the soil moisture increase for consumptive
- irrigation return flow
- water which is not consumptively used
by plants and returns to a surface or ground water supply. Under conditions
of water right litigation, the definition may be restricted to measurable
water returning to the stream from which it was diverted.
- irrigation water
- water which is applied to assist crops
in areas or during times where rainfall is inadequate.
- line that connects points of equal temperature.
- line that connects points of equal rainfall.
- jet stream
- a long narrow meandering current of high-speed
winds near the tropopause blowing from a generally westerly direction
and often exceeding a speed of 250 miles per hour.
- a jet of water.
- one (as a geyser) that sends out a jet.
- a structure (as a pier or mole of wood
or stone) extending into a sea, lake, or river to influence the current
or tide or to protect a harbor.
- a violent surf that occurs on the coast
of the Guinea region, West Africa.
- a short ridge, hill, or mound of stratified
drift deposited by glacial meltwater.
- kame terrace
- a terrace of stratified sand and and gravel
deposited by streams between a glacier and an adjacent valley wall.
- laboratory water
- purified water used in the laboratory
as a basis for making up solutions or making dilutions. Water devoid
of interfering substances.
- lag time
- the time from the center of a unit storm
to the peak discharge or center of volume of the corresponding unit
- a shallow pond where sunlight, bacterial
action, and oxygen work to purify wastewater. Lagoons are typically
used for the storage of wastewaters, sludges, liquid wastes, or spent
- an inland body of water, usually fresh
water, formed by glaciers, river drainage etc. Usually larger than a
pool or pond.
- landscape impoundment
- body of reclaimed water which is used
for aesthetic enjoyment or which otherwise serves a function not intended
to include contact recreation.
- water containing contaminants which leaks
from a disposal site such as a landfill or dump.
- extraction or flushing out of dissolved
or suspended materials from the soil, solid waste, or another medium
by water or other liquids as they percolate down through the medium
- lentic system
- a nonflowing or standing body of fresh
water, such as a lake or pond. Compare lotic system.
- a natural or man-made earthen obstruction
along the edge of a stream, lake, or river. Usually used to restrain
the flow of water out of a river bank.
- rock that consists mainly of calcium carbonate
and is chiefly formed by accumulation of organic remains.
- limiting factor
- factor such as temperature, light, water,
or a chemical that limits the existence, growth, abundance, or distribution
of an organism.
- scientific study of physical, chemical,
and biological conditions in lakes, ponds, and streams.
- a state of matter, neither gas nor solid,
that flows and takes the shape of its container.
- littoral zone
- area on or near the shore of a body of
- lotic system
- a flowing body of fresh water, such as
a river or stream. Compare lentic system.
- cultivation of fish and shellfish in estuarine
and coastal areas. Compare aquiculture.
- an area periodically inundated and treeless
and often characterized by grasses, cattails, and other monocotyledons
- MCL - Maximum Contaminant Level
- the maximum level of a contaminant allowed
in water by federal law. Based on health effects and currently available
- median streamflow
- the rate of discharge of a stream for
which there are equal numbers of greater and lesser flow occurrences
during a specified period.
- the changing of a solid into a liquid.
- water that comes from the melting ice
of a glacier or a snowbank.
- meteoric water
- new water derived from the atmosphere.
- a fabled marine creature usually represented
as having the head, trunk, and arms of a woman and a lower part like
the tail of a fish.
- method blank
- laboratory grade water taken through the
entire analytical procedure to determine if samples are being accidentally
contaminated by chemicals in the lab
- micrograms per liter
- micrograms per liter of water. One thousands
micrograms per liter is equivalent to 1 milligram per liter. This measure
is equivalent to parts per billion (ppb)
- the movement of oil, gas, contaminants,
water, or other liquids through porous and permeable rock.
- milligrams per liter
- milligrams per liter of water. This measure
is equivalent to parts per million (ppm).
- minimum streamflow
- the specific amount of water reserved
to support aquatic life, to minimize pollution, or for recreation. It
is subject to the priority system and does not affect water rights established
prior to its institution.
- municipal sewage
- sewage from a community which may be composed
of domestic sewage, industrial wastes or both.
- natural flow
- the rate of water movement past a specified
point on a natural stream. The flow comes from a drainage area in which
there has been no stream diversion caused by storage, import, export,
return flow, or change in consumptive use caused by man-controlled modifications
to land use. Natural flow rarely occurs in a developed country.
- natural resource
- any form of matter or energy obtained
from the environment that meets human needs.
- National Interim Primary Drinking Water
- a plant nutrient that can cause an overabundance of bacteria and algae when high amounts
are present, leading to a depletion of oxygen and fish kills. Several
forms occur in water, including ammonia, nitrate, nitrite or elemental
nitrogen. High levels of nitrogen in water are usually caused by agricultural
runoff or improperly operating wastewater treatment plants. Also see phosphorous.
- using water in a way that does not reduce
the supply. Examples include hunting, fishing, boating, water-skiing,
swimming, and some power production. Compare consumptive
- noncontact recreation
- recreational pursuits not involving a
significant risk of water ingestion, including fishing, commercial and
recreational boating, and limited body contact incidental to shoreline
activity. Compare contact recreation.
- something which does not allow water to
pass through it. Compare porous.
- nonpoint source
- source of pollution in which wastes are
not released at one specific, identifiable point but from a number of
points that are spread out and difficult to identify and control. Compare point source.
- not suitable for drinking. Compare potable.
- nonthreshold pollutant
- substance or condition harmful to a particular
organism at any level or concentration.
- NPDES permit
- permit issued under the National Pollutant
Discharge Elimination System for companies discharging pollutants directly
into the waters of the United States.
- nephlometric turbidity units.
- as a pollutant, any element or compound,
such as phosphorous or nitrogen,
that fuels abnormally high organic growth in aquatic ecosystems. Also
- having a low supply of plant nutrients.
- open system
- system in which energy and matter are
exchanged between the system and its environment, for example, a living
- organic chemicals
- chemicals containing carbon.
- period of mountain-building.
- orographic precipitation
- rainfall that occurs as a result of warm,
humid air being forced to rise by topographic features such as mountains.
Precipitation on the Edwards Plateau is slightly higher because of the
orographic effect of the escarpment and hills.
- exposed at the surface. The Edwards limestone
outcrops in its recharge zone.
- the place where a wastewater treatment
plant discharges treated water into the environment.
- a deposit of sand and gravel formed by
streams of meltwater flowing from a glacier.
- oxygen demanding waste
- organic water pollutants that are usually
degraded by bacteria if there is sufficient dissolved oxygen (DO) in
- microorganisms which can cause disease.
- peak flow
- in a wastewater treatment plant, the highest
flow expected to be encoutered under any operational conditions, including
periods of high rainfall and prolonged periods of wet weather.
- perched water table
- groundwater standing unprotected over
a confined zone.
- the movement of water through the subsurface
soil layers, usually continuing downward to the groundwater or water
- percolating waters
- waters passing through the ground beneath
the Earth's surface without a definite channel.
- perfected water right
- a water right which indicates that the
uses anticipated by an applicant, and made under permit, were made for
beneficial use. Usually it is irrevocable unless voluntarily canceled
or forfeited due to several consecutive years of nonuse.
- perennial stream
- one that flows all year round. Compare intermittent stream.
- the ability of a water bearing material
to transmit water. It is measured by the quantity of water passing through
a unit cross section, in a unit time, under 100 percent hydraulic gradient.
- numeric value that describes the intensity
of the acid or basic (alkaline) conditions of a solution. The pH scale
is from 0 to 14, with the neutral point at 7.0. Values lower than 7
indicate the presence of acids and greater than 7.0 the presence of
alkalis (bases). Technically speaking, pH is the logarithm of the reciprocal
(negative log) of the hydrogen ion concentration (hydrogen ion activity)
in moles per liter.
- a plant nutrient that can cause an overabundance of bacteria and algae when high amounts
are present, leading to a depletion of oxygen and fish kills. High levels
of phosphorous in water are usually caused by agricultural runoff or
improperly operating wastewater treatment plants. Also see nitrogen.
- plants that send their roots into or below
the capillary zone to use ground water.
- breaking down of parent rock into bits
and pieces by exposure to temperature and changes and the physical action
of moving ice and water, growing roots, and human activities such as
farming and construction. Compare chemical
- free-floating, mostly microscopic aquatic
- piezometroc surface
- the imaginary surface to which groundwater
rises under hydrostatic pressure in wells or springs.
- microscopic floating plant and animal
organisms of lakes, rivers, and oceans.
- plate tectonics
- refers to the folding and faulting of
rock and flow of molten lava involving lithospheric plates in the earth's
crust and upper mantle.
- cement, grout, or other material used
to fill and seal a hole drilled for a water well.
- the area taken up by contaminant(s) in
- pertaining to precipitation.
- point source
- source of pollution that involves discharge
of wastes from an identifiable point, such as a smokestack or sewage
treatment plant. Compare nonpoint source.
- undesireable change in the physical, chemical,
or biological characteristics of the air, water, or land that can harmfully
affect the health, survival, or activities of human or other living
- a body of water usually smaller than a
lake and larger than a pool either naturally or artificially confined.
- something which allows water to pass through
it. Compare nonporous.
- suitable, safe, or prepared for drinking.
- ppb - parts per billion
- number of parts of a chemical found in
one billion parts of a solid, liquid, or gaseous mixture. Equivalent
to micrograms per liter (Ug/L).
- ppm - parts per million
- number of parts of a chemical found in
one million parts of a solid, liquid, or gaseous mixture. Equivalent
to milligrams per liter (mg/L).
- a solid which has come out of an aqueous
solution. (ex., iron from groundwater precipitates to a rust colored
solid when exposed to air).
- a chemical added to a water sample to
keep it stable and prevent compounds in it from changing to other forms
or to prevent microorganism densities from changing prior to analysis.
- price at equilibrium
- where supply and demand curves intersect.
The price at equilibrium is what allocates resources.
- mechanical treatment in which large solids
are screened out and suspended solids in the sewage settle out as sludge.
Compare secondary treatment, tertiary treatment.
- priority date
- the date of establishment of a water right.
It is determined by adjudication of rights established before the passage
of the Water Code. The rights established by application have the application
date as the date of priority.
- profundal zone
- a lake's deep-water region that is not
penetrated by sunlight.
- a small pool of water, usually a few inches
in depth and from several inches to several feet in its greatest dimension.
- a device which moves, compresses, or alters
the pressure of a fluid, such as water or air, being conveyed through
a natural or artificial channel.
- pumped hydroelectric storage
- storing water for future use in generating
electricity. Excess electrical energy produced during a period of low
demand is used to pump water up to a reservoir. When demand is high,
the water is released to operate a hydroelectric generator.
- to force a gas through a water sample
to liberate volatile chemicals or other gases from the water so their
level can be measured.
- purgeable organics
- volatile organic chemicals which can be
forced out of the water sample with relative ease through purging.
- quarry water
- the moisture content of freshly quarried
stone, esp. if porous.
- quicksilver water
- a solution of mercury nitrate used in
- the part of a stream that has a strong
current; an artificial current or bubbling patch of water just astern
of a moving boat.
- water drops which fall to the earth from
- rain gage
- any instrument used for recording and
measuring time, distribution, and the amount of rainfall.
- Resource Conservation and Recovery Act
- federal legislation requiring that hazardous waste be tracked from
"cradle" (generation) to "grave" (disposal).
- receiving waters
- a river, ocean, stream, or other watercourse
into which wastewater or treated effluent is discharged.
- refers to water entering an underground
aquifer through faults, fractures, or direct absorption.
- recharge zone
- the area where a formation allows available
water to enter the aquifer. Generally, that area where the Edwards Aquifer
and associated limestones crop out in Kinney, Uvalde, Medina, Bexar,
Comal, Hays, Travis, and Williamson counties and the outcrops of other
formations in proximity to the Edwards limestone, where faulting and
fracturing may allow recharge of the surface waters to the Edwards Aquifer.
- reclaimed water
- domestic wastewater that is under the
direct control of a treatment plant owner/operator which has been treated
to a quality suitable for a beneficial use.
- recurrence interval
- average amount of time between events
of a given magnitude. For example, there is a 1% chance that a 100-year
flood will occur in any given year.
- amount of a particular resource in known
locations that can be extracted at a profit with present technology
- a pond, lake, tank, or basin (natural
or human made) where water is collected and used for storage. Large
bodies of groundwater are called groundwater reservoirs; water behind
a dam is also called a reservoir of water.
- the available chlorine which remains in
solution after the demand has been satisfied. Compare chlorine demand.
- reverse osmosis
- a water treatment method whereby water
is forced through a semipermeable membrane which filters out impurities.
- right of free
- the idea that the water under a person's
land belongs to that person and they are free to capture and use as
much as they want. Also called the "law of the biggest pump".
- riparian water right
- the legal right held by an owner of land
contiguous to or bordering on a natural stream or lake, to take water
from the source for use on the contiguous land.
- riparian zone
- a stream and all the vegetation on its
- a natural stream of water of considerable
- river basin
- the area drained by a river and its tributaries.
- surface water entering rivers, freshwater
lakes, or reservoirs.
- saline water
- water containing more than 1,000 parts
per million (ppm) of dissolved solids of any type. Compare fresh
- amount of dissolved salts in a given volume
- landfill that is lined with plastic or
concrete or located in clay-rich soils to prevent hazardous substances
from leaking into the environment.
- the condition of a liquid when it has
taken into solution the maximum possible quantity of a given substance
at a given temperature and pressure.
- the impermeable material, such as cement
grout bentonite, or puddling clay placed in the annular space between
the borehole wall and the casing of a water well to prevent the downhole
movement of surface water or the vertical mixing of artestian waters.
- second step in most waste treatment systems,
in which bacteria break down the organic parts of sewage wastes; usually
accomplished by bringing the sewage and bacteria together in trickling
filters or in the activated sludge process. Compare primary treatment,
tertiary treatment. Compare primary treatment, tertiary treatment.
- soil particles, sand, and minerals washed
from the land into aquatic systems as a result of natural and human
- sedimentary cycle
- biogeochemical cycle in which materials
primarily are moved from land to sea and back again.
- a large scale water treatment process
where heavy solids settle out to the bottom of the treatment tank after
- a spot where water contained in the ground
oozes slowly to the surface and often forms a pool; a small spring.
- separate sewer
- a sewer system that carries only sanitary
sewage, not stormwater runoff. When a sewer is constructed this way,
wastewater treatment plants can be sized to treat sanitary wastes only
and all of the water entering the plant receives complete treatment
at all times. Compare combined sewer.
- septic tank
- underground receptacle for wastewater
from a home. The bacteria in the sewage decopose the organic wastes,
and the sludge settles to the bottom of the tank. The effluent flows
out of the tank into the ground through drains.
- settleable solids
- in sewage, suspended solids that will
settle when the sewage is brought to a quiet state for a reasonable
length of time, usually two hours.
- the deposition of finely divided soil
and rock particles upon the bottom of stream and river beds and reservoirs.
- precipitation which is a mixture of rain
- a smooth striated polished surface produced
on rock by movement along a fault.
- solid matter that settles to the bottom
of sedimentation tanks in a sewage treatment plant and must be disposed
of by digestion or other methods or recycled to the land.
- precipitation in the form of branched
hexagonal crystals, often mixed with simple ice crystals, which fall
more or less continuously from a solid cloud sheet. These crystals may
fall either separately or in cohesive clusters forming snowflakes.
- any substance derived from the atmosphere,
vegetation, soil, or rock that is dissolved in water.
- soil erosion
- the processes by which soil is removed
from one place by forces such as wind, water, waves, glaciers, and construction
activity and eventually deposited at some new place.
- a measure of the ability of a water to
conduct an electrical current. Specific conductance is related to the
type and concentration of ions in solution and can be used for approximating
the dissolved solids concentration in water. In general, for the San
Antonio River basin, conductivity * .6 approximates TDS. People monitoring
water quality can measure electrical conductivity quickly in the field
and estimate TDS without doing any lab tests at all. See TDS.
- specific heat
- the amount of heat required to raise the
temperature of a kilogram of a substance (water) by 1 degree Celsius.
- the channel or passageway around or over
a dam through which excess water is diverted.
- spray irrigation
- application of finely divided water droplets
to crops using artificial means.
- an issue of water from the earth; a natural
fountain; a source of a body or reservoir of water.
- standard solution
- any solution in which the concentration
- stormwater discharge
- precipitation that does not infiltrate
into the ground or evaporate due to impervious land surfaces but instead
flows onto adjacent land or water areas and is routed into drain/sewer
- a general term for a body of flowing water.
- stream segment
- refers to the surface waters of an approved
planning area exhibiting common biological, chemical, hydrological,
natural, and physical characteristics and processes. Segments will normally
exhibit common reactions to external stress such as discharge or pollutants.
- the discharge that occurs in a natural
- the transition of water directly from
the solid state to the gaseous state, without passing through the liquid
state; or vice versa. Compare condensation, evaporation.
- sinking down of part of the earth's crust
due to underground excavation, such as removal groundwater.
- a schedule that shows the various quantities
of things offered for sale at various prices at a point in time. Compare demand.
- surface impoundment
- an indented area in the land's surface,
such a pit, pond, or lagoon.
- surface irrigation
- application of water by means other than
spraying such that contact between the edible portion of any food crop
and the irrigation water is prevented.
- surface water
- water that flows in streams and rivers
and in natural lakes, in wetlands, and in reservoirs constructed by
- sustainable management
- method of exploiting a resource that can
be carried on indefinitely. Removal of water from an aquifer in excess
of recharge is, in the long term, not a sustainable management method.
- long term withdrawal from the aquifer
of more water than is being recharged.
- technology-based treatment requirements
- NPDES permit requirements based on the
application of pollution treatment or control technologies including
BTP (best practicable technology), BCT (best conventional technology),
BAT (best available technology economically achievable), and NSPS (new
source performance standards).
- removal from wastewater of traces or organic
chemicals and dissolved solids that remain after primary treatment and secondary treatment.
- the line of maximum depth in a stream.
The thalweg is the part that has the maximum velocity and causes cutbanks
and channel migration.
- thermal gradient
- temperature difference between two areas.
- thermal pollution
- an increase in air or water temperature
that disturbs the climate or ecology of an area.
- fairly thin zone in a lake that separates
an upper warmer zone (epilimnion) from a lower colder zone (hypolimnion).
- threshold pollutant
- substance that is harmful to a particular
organism only above a certain concentration, or threshold level.
- TDS - total dissolved
- the sum or all inorganic and organic particulate
material. TDS is an indicator test used for wastewater analysis and
is also a measure of the mineral content of bottled water and groundwater.
There is a relationship between TDS and conductivity. In general, for
the San Antonio River basin, TDS/.6 approximates conductivity. Or, conductivity
* .6 approximates TDS. People monitoring water quality can measure electrical
conductivity quickly in the field and estimate TDS without doing any
lab tests at all. See specific conductance.
- Toxicity Reduction Evaluation (TRE)
- a study conducted to determine the source(s)
of toxicity in a discharge effluent so that these sources can be controlled
sufficiently to allow a discharger to comply with their permit limits.
- toxicity test
- the means to determine the toxicity of
a chemical or an effluent using living organisms. A toxicity test measures
the degree of response of an exposed test organism to a specified chemical
- Tragedy of the Commons
- the idea that no one takes responsibility
for things that everybody owns.
- refers to the rate at which limestone
allows the transmission of water. Limestone can be highly porous, but
not very transmissive if the pores are not connected to each other.
Technically speaking, it is the rate at which water is transmitted through
a unit width of aquifer under unit hydraulic gradient. Transmissivity
is directly proportional to aquifer thickness, thus it is high where
the Edwards is thick and low where it is thin, given the same hydraulic
- direct transfer of water from the leaves
of living plants to the atmosphere. Distinguish evapotranspiration.
- a stream that contributes its water to
another stream or body of water.
- thick or opaque with matter in suspension.
Rivers and lakes may become turbid after a rainfall.
- the layer of atmosphere closest to the
Earth, extending seven to ten miles above the surface, containing most
of the clouds and moisture.
- United States Geological Survey
- unclassified waters
- those waters for which no classification
has been assigned and which have not been identified in Appendix A of
31 Texas Administrative Code, Chapter 307.10 of Title 31 (relating to
- unconsolidated formations
- naturally occurring earth formations that
have not been lithified. Alluvium, soil, gravel, clay, and overburden
are some of the terms used to describe this type of formation.
- a current below the upper currents or
surface of a fluid body.
- a concealed drain with openings through
which the water enters when the water table reaches the level of the
- movement of water through subsurface material.
- the current beneath the surface that sets
seaward or along the beach when waves are breaking on the shore.
- under the surface of the water; lying,
growing, performed, worn, or operating below the surface of the water,
as underwater caverns, underwater operation of a submarine.
- an upward flow.
- vested water right
- the right granted by a state water agency
to use either surface or ground water.
- virgin flow
- the streamflow which exists or would exist
if man had not modified the conditions on or along the stream or in
the drainage basin.
- the pore space or other openings in rock.
The openings can be very small to cave size and are filled with water
below the water table.
- water containing waste including greywater,
blackwater or water contaminated by waste contact, including process-generated
and contaminated rainfall runoff.
- the liquid that descends from the clouds
as rain; forms streams, lakes, and seas, and is a major constituent
of all living matter. It is an odorless, tasteless, colorless, very
slightly compressible liquid.
- water cycle
- natural pathway water follows as it changes
between liquid, solid, and gaseous states; biogeochemical cycle that
moves and recycles water in various forms through the ecosphere. Also
called the hydrologic cycle.
- water pollution
- degradation of a body of water by a substance
or condition to such a degree that the water fails to meet specified
standards or cannot be used for a specific purpose.
- water quality-based toxics control
- an integrated strategy used in NPDES permitting
to assess and control the discharge of toxic pollutants to surface waters.
There are two approaches: the whole-effluent approach involves the use
of toxicity tests to measure discharge toxicity; the chemical specific
approach involves the use of water quality criteria or State standards
to limit specific toxic pollutants directly.
- water quality criteria
- scientifically derived ambient limits
developed and updated by EPA, under section 304(a)(1) of the Clean Water
Act, for specific pollutants of concern. Criteria are recommended concentrations,
levels, or narrative statements that should not be exceeded in a waterbody
in order to protect aquatic life or human health.
- water quality standards
- laws or regulations, promulgated under
Section 303 of the Clean Water Act, that consist of the designated use
or uses of a waterbody or a segment of a waterbody and the water quality
criteria that are necessary to protect the use or uses of that particular
waterbody. Water quality standards also contain an antidegradation statement.
Every State is required to develop water quality criteria standards
applicable to the various waterbodies within the State and revise them
every 3 yeaars.
- water table
- level below the earth's surface at which
the ground becomes saturated with water. The surface of an unconfined
aquifer which fluctuates due to seasonal precipitation.
- water table aquifer
- an aquifer confined only by atmospheric
pressure (water levels will not rise in the well above the confining
- water well
- any artificial excavation constructed
for the purpose of exploring for or producing ground water.
- water year
- The 12-month period, usually October 1
through September 30. The water year is designated by the calendar year
in which it ends and which includes 9 of the 12 months. Thus, the year
ending September 30, 1998 is called the1998 Water Year.
- A sudden, nearly vertical drop in a stream,
as it flows over rock.
- saturation of soil with irrigation water
so the water table rises close to the surface.
- An employee of a water department who
distributes available water supply at the request of water right holders
and collects hydrographic data.
- land area from which water drains toward
a common watercourse in a natural basin.
- day to day variation in atmospheric conditions.
- area that is regularly wet or flooded
and has a water table that stands at or above the land surface for at
least part of the year, such as a bog, pond, fen, estuary, or marsh.
- whole-effluent toxicity
- the aggregate toxic effect of an effluent
measured directly by a toxicity test.
- creative landscaping for water and energy
efficiency and lower maintenance. The seven xeriscape principles are:
good planning and design; practical lawn areas; efficient irrigation;
soil improvement; use of mulches; low water demand plants; good maintenance.
- the quantity of water expressed either
as a continuous rate of flow (cubic feet per second, etc.) or as a volume
per unit of time. It can be collected for a given use, or uses, from
surface or groundwater sources on a watershed.
- zone of aeration
- a region in the Earth above the water
table. Water in the zone of aeration is under atmospheric pressure and
will not flow into a well.
- zone of saturation
- the space below the water table in which
all the interstices (pore spaces) are filled with water. Water in the
zone of saturation is called groundwater.
- tiny aquatic animals eaten by fish.