Glossary of Geologic & Water Terminology
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Index
|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|
A
Ablation:
The process by which ice and snow waste away owing to melting and evaporation.
Absorption:
The entrance of water into the soil or rocks by all natural processes.
Acre-Foot:
A unit for measuring the volume of water, is equal to the quantity of water required to cover 1 acre to a depth of 1 foot and is equal to 43,560 cubic feet or 325,851 gallons. The term is commonly used in measuring volumes of water used or stored.
Aeration zone:
(also known as the unsaturated zone) The zone above the water table is known as the aeration zone.
Anabranch:
A diverging branch of a river which reenters the mainstream.
Anchor Ice:
Ice in the bed of a stream or upon a submerged body or structure.
Annual Flood:
The highest peak discharge in a water year.
Antecedent Precipitation Index:
An index of moisture stored within a drainage basin before a storm.
Area-Capacity Curve:
A graph showing the relation between the surface area of the water in a reservoir and the corresponding volume.
Artesian aquifer:
See confined aquifer
Aquifer:
An underground geological formation able to store and yield water.
Average Discharge:
In the annual series of the Geological Survey's reports on surface-water supply--the arithmetic average of all complete water years of record whether or not they are consecutive. Average discharge is not published for less than 5 years of record.
The term "average" is generally reserved for average of record and "mean" is used for averages of shorter periods, namely, daily mean discharge.
B
Backwater:
Water backed up or retarded in its course as compared with its normal or natural condition of flow. In stream gaging, a rise in stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below.
The difference between the observed stage and that indicated by the stage-discharge relation, is reported as backwater.
Bank:
The margins of a channel. Banks are called right or left as viewed facing in the direction of the flow.
Bankfull Stage:
Stage at which a stream first overflows its natural banks. Bankfull stage is a hydraulic term, whereas flood stage implies damage.
Base Discharge:
In the Geological Survey's annual reports on surface-water supply, the discharge above which peak discharge data are published. The base discharge at each station is selected so
that an average of about three peaks a year will be presented.
Base flow: or Base Runoff:
Sustained or fair weather runoff. In most streams, base runoff is composed largely of groundwater effluent. (Langbein and others, 1947, p. 6.) The term base flow is often used in the same sense as base runoff. However, the
distinction is the same as that between streamflow and runoff. When the concept in the terms base flow and base runoff is that of the natural flow in a stream, base runoff is the logical term.
Basic Hydrologic Data:
Includes inventories of features of land and water that vary only from place to place (topographic and geologic maps are examples), and records of processes that vary with both place and time. (Records of precipitation,
streamflow, ground-water, and quality-of-water analyses are examples.)
Braiding of River Channels:
Successive division and rejoining (of riverflow) with accompanying islands is the important characteristic denoted by the synonymous terms, braided or anastomosing stream. A braided stream is composed of anabranches.
C
Capillary water:
Just above the water table, in the aeration zone, is capillary water that moves upward from the water table by capillary action. This water can move slowly
and in any direction. While most plants rely upon moisture from precipitation that is present in the unsaturated zone, their roots may also tap into capillary water or into the underlying
saturated zone.
Collection site:
A stream, lake, reservoir, or other body of water fed by water drained from a watershed.
Condensation:
The process in the hydrologic cycle by which a vapor becomes a liquid; the opposite of evaporation.
Confined Aquifer:
(also known as artesian or pressure aquifers) exist where the groundwater is bounded between layers of impermeable substances like clay or dense rock. When
tapped by a well, water in confined aquifers is forced up, sometimes above the soil surface. This is how a flowing artesian well is formed.
Conservation:
The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming, and industry, and thus increasing water supplies for optimum
long-term economic and social benefits.
Consumptive Use:
The use of a resource that reduces the supply (removing water from a source like a river or lake without returning an equal amount). Examples include the
intake of water by plants, humans, and other animals and the incorporation of water into the products of industrial or food processing.
Contaminant:
Any substance that when added to water (or another substance) makes it impure and unfit for consumption or use.
D
Depletion:
The loss of water from surface water reservoirs or groundwater aquifers at a rate greater than that of recharge.
Diffusion:
The movement of a substance from an area of high concentration to an area of low concentration.
Discharge:
An outflow of water from a stream, pipe, groundwater aquifer, or watershed; the opposite of recharge.
Drought:
An extended period with little or no precipitation; often affects crop production and availability of water supplies.
E
Erosion:
The wearing down or washing away of the soil and land surface by the action of water, wind, or ice.
Evaporation:
The conversion of a liquid (water) into a vapor (a gaseous state) usually through the application of heat energy during the hydrologic cycle; the opposite of condensation.
Evapotranspiration:
The loss water from the soil through both evaporation and transpiration from plants.
F
Fresh water:
Water with less than 0.5 parts per thousand dissolved salts.
G
Gas (gaseous):
See vapor.
Groundwater:
Water found in the spaces between soil particles and cracks in rocks underground (located in the saturation zone). Groundwater is a natural resource that is used for drinking, recreation, industry, and growing crops.
H
Hydrologic cycle:
(also known as the water cycle) The paths water takes through its various states--vapor, liquid, solid--as it moves throughout the ocean, atmosphere, groundwater, streams, etc.
I
Impermeable Layer:
A layer of material (clay) in an aquifer through which water does not pass.
Irrigation:
The controlled application of water to cropland, hay fields, and/or pasture to supplement that supplied by nature.
J
K
L
Liquid:
The part of the hydrologic cycle in which molecules move freely among themselves but do not separate like those in a vapor/gaseous state.
M
Municipal Water System:
A network of pipes, pumps, and storage and treatment facilities designed to deliver potable water to homes, schools, businesses, and other users in a city or town and to remove and treat waste materials.
N
Non-point Source Pollution:
Wide-spread overland runoff containing pollutants; the contamination does not originate from one specific location, and pollution discharges over a wide land area.
O
Permeable:
Capable of transmitting water (porous rock, sediment, or soil).
P
Permeable Layer:
A layer of porous material (rock, soil, unconsolidated sediment); in an aquifer, the layer through which water freely passes as it moves through the ground.
Plume:
A continuous emission from a point source of contamination that has a starting point and a noticeable pathway.
Point Source Pollution:
Pollutants discharged from any identifiable point, including pipes, ditches, channels, sewers, tunnels, and containers of various types.
Pollution:
An alteration in the character or quality of the environment, or any of its components, that renders it less suited for certain uses. The alteration of the physical,
chemical, or biological properties of water by the introduction of any substance that renders the water harmful to use.
Precipitation:
The part of the hydrologic cycle when water falls, in a liquid or solid state, from the atmosphere to Earth (rain, snow, sleet).
Q
R
Recharge:
Groundwater supplies are replenished, or recharged, when water enters the saturation zone by actions like rain or snow melt.
Ridge lines:
Points of higher ground that separate two adjacent streams or watersheds; also known as divides.
Runoff:
Precipitation that flows over land to surface streams, rivers, and lakes.
S
Salinization:
The condition in which the salt content of soil accumulates over time to above normal levels; occurs in some parts of the world where water containing high salt
concentration evaporates from fields irrigated with standing water.
Salt marsh:
A low coastal grassland frequently inundated by the tide.
Salt Water:
Water that contains a relatively high percentage (over 0.5 parts per thousand) of salt minerals.
Saturation Zone:
The portion below the earth's surface that is saturated with water is called the zone of saturation. The upper surface of this zone, open to atmospheric pressure,
is known as the water table.
Soil:
The top layer of the Earth's surface, containing unconsolidated rock and mineral particles mixed with organic material.
Storm drain:
Constructed opening in a road system through which runoff from the road surface flows into an underground system.
Sublimation:
The transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase.
Substrate:
A layer of material beneath the surface soil.
Surface water:
Water above the surface of the land, including lakes, rivers, streams, ponds, floodwater, and runoff.
T
Temporary Wetland:
A type of wetland in which water is present for only part of the year, usually during the wet or rainy seasons; also known as vernal pools.
Transpiration:
The process by which water absorbed by plants (usually through the roots) is evaporated into the atmosphere from the plant surface (principally from the leaves).
U
Unconfined Aquifers:
An aquifer in which the upper boundary is the water table.
V
Vapor:
The state of water in the hydrologic cycle in which individual molecules are highly energized and move about freely; also known as gas/gaseous.
W
Wastewater:
Water that contains unwanted materials from homes, businesses, and industries; a mixture of water and dissolved or suspended substances.
Wastewater Treatment:
Any of the mechanical or chemical processes used to modify the quality of wastewater in order to make it more compatible or acceptable to humans and the environment.
Water (H2O):
An odorless, tasteless, colorless liquid made up of a combination of hydrogen and oxygen. Water forms streams, lakes, and seas, and is a major constituent of all living matter.
Water-Bearing Rocks:
Several types of rocks can hold water, including: sedimentary deposits (sand and gravel), channels in carbonate rocks (limestone), lava tubes or cooling
fractures in igneous rocks, and fractures in hard rocks.
Water Cycle:
See Hydrologic Cycle.
Water Quality:
The chemical, physical, and biological characteristics of water with respect to its suitability for a particular use.
Water Quality Standard:
Recommended or enforceable maximum contaminant levels of chemicals or materials (such as chlorobenzene, nitrate, iron, arsenic) in water. These levels are established
for water used by municipalities, industries, agriculture, and recreationists.
Watershed:
The land area from which surface runoff drains into a stream, channel, lake, reservoir, or other body of water; also called a drainage basin.
Water Table:
The top of an unconfined aquifer; indicates the level below which soil and rock are saturated with water.
Water Treatment Plants:
Facilities that treat water to remove contaminants so that it can be safely used.
Well Field:
An area in which productive wells are drilled (similar to an oil field).
Wetlands:
Lands where water saturation is the dominant factor in determining the nature of soil development and the types of plant and animal communities. Other common names for
wetlands are sloughs, ponds, and marshes.
X
Xeriscaping:
An environmentally friendly form of landscaping that uses a variety of indigenous and drought-tolerant plants, shrubs, and ground cover.
Y
Z
"Parts of this material was reproduced from groundwater.org with the permission of The Groundwater Foundation.
Copyright ©2002 The Groundwater Foundation. All Rights Reserved."
Catchment Area:
See Drainage Basin.
CFS:
Abbreviation for Cubic Feet per Second.
CFS-Day
The volume of water represented by a flow of 1 cubic foot per second for 24 hours. It equals 86,400 cubic feet, 1.983471 acre-feet, or 646,317 gallons.
CFSM:
(Cubic Feet per Second per square Mile). The average number of cubic feet of water per second flowing from each square mile of area drained by a stream, assuming that the runoff is distributed uniformly in time and area.
A unit expressing rates of discharge. One cubic foot per second is equal to the discharge of a stream of rectangular cross section, 1 foot wide and 1 foot deep, flowing water an average velocity of 1 foot per second./dd>
Channel:
An open conduit either naturally or artificially created which periodically or continuously contains moving water, or which forms a connecting link between two bodies of water. River, creek, run, branch, anabranch, and tributary are
some of the terms used to describe natural channels. Natural channels may be single or braided.
Channel Storage:
The volume of water at a given time in the channel or over the flood plain of the streams in a drainage basin or river reach. Channel storage is great during the progress of a flood event.
Climate:
The sum total of the meteorological elements that characterize the average and extreme condition of the atmosphere over a long period of time at any one place or region of the earth's surface. The collective state of the atmosphere at a
given place or over a given area within a specified period of time.
Climatic Year:
A continuous 12-month period during which a complete annual cycle occurs, arbitrarily selected for the presentation of data relative to hydrologic or meteorologic phenomena. The climatic year is usually designated by the calendar
year during which most of the 12 months occur.
Cloudburst:
A torrential downpour of rain, which by its spottiness and relatively high intensity suggests the bursting and discharge of a whole cloud at once.
Concentration time: or Time of Concentration:
The time required for water to flow from the farthest point on the watershed to the gaging station.
Concordant Flows:
Flows at different points in a river system that have the same recurrence interval, or the same frequency of occurrence. It is most often applied to floodflows.
Condensation:
The process by which water changes from the vapor state into the liquid or solid state. It is the reverse of evaporation.
Conservation Storage:
Storage of water for later release for useful purposes such as municipal water supply, power, or irrigation in contrast with storage capacity used for flood control.
Consumptive Use:
The quantity of water absorbed by the crop and transpired or used directly in the building of plant tissue together with that evaporated from the cropped area.
Consumptive Waste:
The water that returns to the atmosphere without benefiting man.
Contents:
The volume of water in a reservoir. Unless otherwise indicated reservoir content is computed on the basis of a level pool and does not include bank storage.
Control:
A natural constriction of the channel, a long reach of the channel, a stretch of rapids, or an artificial structure downstream from a gaging station that determines the stage-discharge relation at the gage. A control may be
complete or partial. A complete control exists where the stage-discharge relation at a gaging station is entirely independent of fluctuations in stage downstream from the control. A partial control exists
where downstream fluctuations have some effect upon the stage-discharge relation at a gaging station. A control, either partial or complete, may also be shifting. Most natural controls are shifting to a
degree, but a shifting control exists where the stagedischarge relation experiences frequent changes owing to impermanent bed or banks.
Correlation:
The process of establishing a relation between a variable and one or more related variables. Correlation is simple if there is only one independent variable; multiple, if there is more than one independent variable.
For gaging station records, the usual variables are the short-term gaging-station record and one or more long-term gaging-station records.
Correlative Estimate:
A discharge determined by correlation. A correlative estimate represents a likely value of the discharge for any particular period--commonly a month--according to a specified method of analysis.
Cryology:
Science of ice and snow.
Current Meter:
An instrument for measuring the speed of flowing water. The Geological Survey uses a rotating cup meter.
Cusec:
This abbreviation for cubic foot per second, common in the British Commonwealth countries (except Canada), is not used by the U.S. Geological Survey; instead, CFS is used.
Cycle:
A regularly recurring succession of events such as the cycle of the seasons. Use of cycle to describe a group of wet years followed or preceded by a group of dry years is to be avoided.
Dead Storage:
The volume in a reservoir below the lowest controllable level.
Dependable Yield:
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.
Depletion:
The progressive withdrawal of water from surface- or ground-water reservoirs at a rate greater than that of replenishment.
Depression Storage:
The volume of water contained in natural depressions in the land surface, such as puddles.
Direct Runoff:
The runoff entering stream channels promptly after rainfall or snowmelt. Superposed on base runoff, it forms the bulk of the hydrograph of a flood.
Discharge:
In its simplest concept discharge means outflow; therefore, the use of this term is not restricted as to course or location, and it can be applied to describe the flow of water from a pipe or from a drainage basin.
If the discharge occurs in some course or channel, it is correct to speak of the discharge of a canal or of a river. It is also correct to speak of the discharge of a canal or stream into a lake, a stream, or an ocean.
Diversion:
The taking of water from a stream or other body of water into a canal, pipe, or other conduit.
Double-Mass Curve:
A plot on arithmetic cross-section paper of the cumulated values of one variable against the cumulated values of another or against the computed values of the same variable for a concurrent period of time.
Drainage Area:
The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is enclosed by a drainage divide.
Drainage Basin:
A part of the surface of the earth that is occupied by a drainage system, which consists of a surface stream or a body of impounded surface water together with all tributary surface streams and bodies of impounded surface water.
Drainage Density:
Length of all channels above those of a specified stream order per unit of drainage area.
Drainage Divide:
The rim of a drainage basin.
Drought:
A period of deficient precipitation or runoff extending over an indefinite number of days, but with no set standard by which to determine the amount of deficiency needed to constitute a drought. Thus, there is no
universally accepted quantitative definition of drought; generally, each investigator establishes his own definition. The following paragraph discusses the problem of defining a drought:
When in an area that is ordinarily classed as humid, natural vegetation becomes desiccated or defoliates unseasonably and crops fail to mature owing to lack of precipitation, or when precipitation
is insufficient to meet the needs of established human activities, drought conditions may be said to prevail. Although water for irrigation or other uses in arid areas is always limited, special
shortages in such areas are also regarded as droughts. Unsatisfactory distribution of precipitation throughout the year may be as effective a factor in causing a drought as a shortage in the
total amount. Temperature and wind may also play an important part, especially in relation to the damage done.
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Glossary of Geologic & Water Terminology