HYDROLOGIC TERMS

8/10/2019 HYDROLOGIC TERMS

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1. Ablation- The process by which ice and snow dissipate owing to melting and evaporation.

2. Absorption- The process by which substances in gaseous, liquid or solid form dissolve or

mix with other substances.

3. Acre-foot- The amount of water required to cover one acre to a depth of one foot. n acre-

foot equals 32!,"#1 gallons, or $3,#!% cubic feet.

$. Adhesion& molecular attraction between the surfaces of two bodies in contact.

#. Adsorption- dherence of gas molecules, ions, or molecules in solution to the surface of

solids.

!. Adsorption isotherm- graphical representation of the relationship between the bul'

activity of adsorbate and the amount adsorbed at constant temperature.

(. Advection- The process whereby solutes are transported by the bul' mass of flowing fluid.

". Aggressive )water* & water that corrodes manmade and+or geological materials.

. Air-space-ratio- The ratio of )a* the volume of water that can be drained from a saturated

soil or roc' under the action of force of gravity to )b* the total volume of voids.

1%. Albedo- The measure of how much solar radiation is reflected from arths surface. The

balance between the amount of solar radiation reflected and absorbed by arths surface plays

an important role in regulating global temperature.

11. Anhydrous& destitute of water.

12. Anisotropy- The condition of having different properties in different directions.


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13. Anisotropic mass- mass having different properties in different directions at any given

point.

1$. Aquiclude- hydrogeologic unit which, although porous and capable of storing water, does

not transmit it at rates sufficient to furnish an appreciable supply for a well or spring.

1#. Aquifer- formation, group of formations, or part of a formation that contains sufficient

saturated permeable material to yield significant quantities of water to wells and springs.

1!. Aquifer system- body of permeable and poorly permeable material that functions

regionally as a water-yielding unit/ it comprises two or more permeable beds separated at

least locally by confining beds that impede groundwater movement but do not greatly affect

the regional hydraulic continuity of the system/ includes both saturated and unsaturated parts

of permeable material.

1(. Aquifer test- test to determine hydrologic properties of the aquifer involving the

withdrawal of measured quantities of water from or addition of water to a well and the

measurement of resulting changes in head in the aquifer both during and after the period of

discharge or additions.

1". Aquifuge- hydrogeologic unit which has no interconnected openings and, hence cannot

store or transmit water.

1. Aquitard- confining bed that retards but does not prevent the flow of water to or from an

ad0acent aquifer/ a lea'y confining bed. t does not readily yield water to wells or springs, but

may serve as a storage unit for ground water.


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2%. Area of influence of a well - The area surrounding a pumping or recharging well within

which the potentiometric surface has been changed.

21. Artesian well- well deriving its water from an artesian or confined aquifer.

22. Artificial recharge - echarge at a rate greater than natural, resulting from deliberate or

incidental human activities.

23. Attenuation- The process where the flood crest is reduced as it progresses downstream.

2$. Bail test& a test of media hydraulic properties )typically permeability and storativity* in

which a volume of water is withdrawn instantaneously )bailed* from a well or pieometer

and its response measured and analyed. 4ee also slug test.

2#. Bailer& a )usually cylindrical* device for withdrawing or collecting water from a well or

borehole.

2!. Bank storage - water in an alluvial system that was recharged by the ad0acent stream during

the rising limb of a streamflow hydrograph.

2(. Base flow - That part of the stream discharge that is not attributable to direct runoff from

precipitation or melting snow/ it is usually sustained by groundwater discharge.

2". Baseline monitoring- The establishment and operation of a designed surveillance system

for continuous or periodic measurements and recording of existing and changing conditions

that will be compared with future observations.

2. Basin Boundary- The topographic dividing line around the perimeter of a basin, beyond

which overland flow )i.e. runoff* drains away into another basin.


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3%. Basin Recharge- ainfall that adds to the residual moisture of the basin in order to help

recharge the water deficit, i.e. water absorbed into the soil that does not ta'e the form of

direct runoff.

31. Breakthrough curve - plot of relative concentration versus time, where relative

concentration is defined as 5+5o with 5 as the concentration at a point in the groundwater

flow domain, and 5o as the source concentration.

32. Buildup- The vertical distance the water table or potentiometric surface is raised, or the

increase of the pressure head due to the addition of water.

33. Capillary action- The movement of water in the interstices of a porous medium due to

capillary forces.

3$. Capillary conductivity - The property of an unsaturated porous medium to transmit liquid.

3#. Capillary fringe- The lower subdivision of the unsaturated one immediately above the

water table in which the interstices are filled with water under pressure less than that of the

atmosphere, being continuous with the water below the water table but held above it by

capillary forces.

3!. Capillary head- The potential, expressed in head of water that causes the water to flow by

capillary action.

3(. Capillary potential- The scalar quantity that represents the wor' required to move a unit

mass of water from the soil to a chosen reference location and energy state.


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3". Capillary pressure- The difference in pressure across the interface between two immiscible

fluid phases 0ointly occupying the interstices of a porous medium caused by interfacial

tension between the two phases.

3. Capillary rise- The height above a free water surface to which water will rise by capillary

action.

$%. Capillary water- 6ater held in the soil above the phreatic surface by capillary forces.

$1. Cascading water- n reference to wells, groundwater that tric'les or pours through crac's or

perforations down the casing or uncased borehole above the water level in the well.

$2. Cation exchange capacity - The sum total of exchangeable cations that a porous medium

can absorb. xpressed in moles of ion charge per 'ilogram of soil .

$3. CF !Cubic Feet per econd" - The flow rate or discharge equal to one cubic foot of water

per second. This rate is equivalent to approximately (.$" gallons per second.

$$.

$#. Concentration gradient- The change in solute concentration per unit distance in solute.

5oncentration gradients cause 7ic'ian diffusion )spreading* of solutes from regions of

highest to regions of lowest concentrations. n slow moving groundwater, this is the

dominant mixing process.

#$% Cone of depression - depression of the potentiometric surface in the shape of an inverted

cone that develops around a well which is being pumped.


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$(. Cone of impression - rise of the potentiometric surface in the shape of a cone that

develops around an in0ection well.

$". Confined- modifier which describes a condition in which the potentiometric surface is

above the top of the aquifer.

$. Connate water - 6ater entrapped in the interstices of a sedimentary or extrusive igneous

roc' at the time of its deposition.

#%. Contaminant- n undesirable substance not normally present or an unusually high

concentration of a naturally occurring substance in water or soil.

#1. Contamination- The addition to water of any substance or property preventing the use or

reducing the usability of the water. 4ometimes considered synonymous with

pollution. 5ontaminant plume - n elongated body of groundwater containing contaminants,

emanating and migrating from a point source within a hydrogeologic unit)s*.

#2. Convective transport - The component of movement of heat or mass induced by thermal

gradients in groundwater.

#3. Convection- The process whereby heat is carried along with the flowing groundwater.

#$. &arcy's law - n empirical law which states that the velocity of flow through d porous

medium is directly proportional to the hydraulic gradient assuming that the flow is laminar

and inertia can be neglected.


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##. &ebris Flow - moving mass of loose mud, sand, soil, roc', water and air that travels

downslope )often rapidly*. To be considered a debris flow, more than half of the solids in the

mass must be larger than sand grains. 8ud flows are the finer-grained, more watery

counterparts of debris flows.

#!.

#(. &eep percolation - The drainage of soil water downward by gravity below the maximum

effective depth of the root one toward storage in subsurface strata.

#". &esorption - The reverse process of sorption.

#. &ischarge area - n area in which groundwater is discharged to the land surface, surface

water, or atmosphere.

!%. &ifferential water capacity - The absolute value of the rate of change of water content with

soil water pressure. The water capacity at a given water content will depend on the particular

desorption or adsorption curve employed. 9istinction should be made between volumetric

and specific water capacity.

!1. &iffusion- :rocess whereby ionic or molecular constituents move under the influence of

their 'inetic activity in the direction of their concentration gradient.

!2. &irect Runoff- The runoff entering stream channels promptly after rainfall or snow melt.

4uperposed on base runoff, it forms the bul' of the hydrograph of a flood.


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!3. &ispersivity- geometric property of a porous medium which determines the dispersion

characteristics of the medium by relating the components of pore velocity to the dispersion

coefficient.

!$. &ispersion coefficient - measure of the spreading of a flowing substance due to the nature

of the porous medium, with its interconnected channels distributed at random in all

directions.

!#. &ispersivity- geometric property of a porous medium which determines the dispersion

characteristics of the medium by relating the components of pore velocity to the dispersion

coefficient.

!!. &isposal well - well used for the disposal of waste into a subsurface stratum.

!(. &istribution coefficient- The quantity of the solute, chemical or radionuclide absorbed by

the solid per unit weight of solid divided by the quantity dissolved in the water per unit

volume of water.

!". &rainage &ivide- The boundary line, along a topographic ridge or along a subsurface

formation, separating two ad0acent drainage basins.

!.

(%. &rainage well- well installed to drain surface water, storm water, or treated waste water

into underground strata. water well-constructed to remove subsurface water or to reduce a

hydrogeologic units potentiometric surface.


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(1. &rawdown- The vertical distance the water elevation is lowered or the reduction of the

pressure head due to the removal of water. The decline in potentiometric surface at a point

caused by the withdrawal of water from a hydrogeologic unit.

(2. (ffective )recipitation )ainfall* - That part of the precipitation that produces runoff.

(3. (lectrical conductivity- 8easure of the ability of material to conduct an electrical current.

7or water samples, it depends on the concentration and type of ionic constituents in the water

and temperature of the water/ and it is expressed in siemens per meter.

($. (quipotential line)or surface* - ;ine )or surface* along which the potential is constant.

(#. (vapotranspiration- The combined loss of water from a given area by evaporation from the

land and transpiration from plants.

(!. (xchange capacity-The amount of exchangeable ions measured in moles of ion change per

'ilogram of solid material at a given p


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"%. Flow net- graphical representation of flow lines and equipotential lines for two-

dimensional, steady-state groundwater flow.

"1. Flow path- The subsurface course a water molecule or solute would follow in a given

groundwater velocity field.

"2. Fluid potential- The mechanical energy per unit mass of a fluid at any given point in space

and time with regard to an arbitrary state and datum.

"3. Fresh water- 6ater that contains less than 1,%%% milligrams per liter )mg+;* of dissolved

solids/ generally more than #%% mg+; is undesirable for drin'ing and many industrial uses.

"$. *aining stream- stream or reach of a stream whose flow is being increased by inflow of

groundwater.

"#. *ravitational head- The component of total hydraulic head related to the position of a

given mass of water relative to an arbitrary datum.

"!. *ravitational water- 6ater which moves into, through, or out of the soil or roc' mass

under the influence of gravity.

"(. *roundwater- That part of the subsurface water that is in the saturated one. ;oosely, all

subsurface water as distinct from surface water. ll water which occurs below the land

surface. t includes both water within the unsaturated and saturated ones.

"". *roundwater barrier- oc' or artificial material which has a relatively low permeability

and which occurs below the land surface where it impedes the movement of ground water


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and consequently causes a pronounced difference in the potentiometric surface on opposite

sides of it.

". *roundwater basin- general term used to define a groundwater flow system that has

defined boundaries and may include permeable materials that are capable of storing or

furnishing a significant water supply, the basin includes both the surface area and the

permeable materials beneath it.

%. *roundwater flow- The movement of water in the one of saturation.

1. *roundwater flux- 4ee specific discharge. The rate of groundwater flow per unit area of

porous or fractured media measured perpendicular to the direction of flow

2. *roundwater &ivide- line on a water table where on either side of which the water table

slopes downward. t is analogous to a drainage divide between two drainage basins on a land

surface.

3. *roundwater mound- raised area in a water table or other potentiometric surface created

by groundwater recharge.

$. *roundwater Runoff- That part of the runoff which has infiltrated into the ground to

become groundwater, and is discharged into a stream channel as spring, or seepage water.

#. +eterogeneity- characteristic of a medium in which material properties vary from point to

point.

!. +omogeneity- characteristic of a medium in which material properties are identical

everywhere.


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(. +ydraulic barrier- general term referring to modifications of a groundwater flow system

to restrict or impede movement of contaminants.

". +ydraulic conductivity- proportionality constant relating hydraulic gradient to specific

discharge which for an isotropic medium and homogeneous fluid, equals the volume of water

at the existing 'inematic viscosity that will move in unit time under a unit hydraulic gradient

through a unit area measured at right angles to the direction of flow.

. +ydraulic head- The height above a datum plane )such as sea level* of the column of water

that can be supported by the hydraulic pressure at a given point in a ground water system. 7or

a well, the hydraulic head is equal to the distance between the water level in the well and the

datum plane.

1%%. +ydrochemical facies- 9istinct ones that have cation and anion concentrations of

diagnostic chemical character of water solutions in hydrologic systems which is describable

within defined composition categories.

1%1. +ydrodynamic dispersion - The spreading )at the macroscopic level* of the solute front

during transport resulting from both mechanical dispersion and molecular diffusion .

1%2. +ydrogeologic unit - ny soil or roc' unit or one which by virtue of its hydraulic

properties has a distinct influence on the storage or movement of groundwater. 8eans any

soil or roc' unit or one which by virtue of its porosity or permeability, or lac' thereof, has a

distinct influence on the storage or movement of groundwater.


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1%3. +ydrograph- graph relating stage, flow, velocity, or other characteristics of water

with respect to time.

1%$. +ydrologic properties - Those properties of a roc' that govern the entrance of water and

the capacity to hold, transmit, and deliver water, such as porosity, effective porosity, specific

retention, permeability, and the directions of maximum and minimum permeability.

1%#. +ydrologic Budget- n accounting of the inflow to, outflow from, and storage in, a

hydrologic unit, such as a drainage basin, aquifer, soil one, la'e or reservoir.

1%!. +ydrophobicity- The property of repelling, tending not to combine with, or incapable of

dissolving in water.

1%(. ,mmiscible- Two or more liquids that are not readily soluble. The chemical property of

two or more phases that, at mutual equilibrium, cannot dissolve completely in one another,

e.g. oil and water.

1%". ,mpermeable- characteristic of some geologic material that limits its ability to

transmit significant quantities of water under the head differences ordinarily found in the

subsurface.

1%. ,mpervious- The ability to repel water, or not let water infiltrate.

11%. ,nfiltration- The downward entry of water into the soil or roc'.

111. ,nfiltration capacity- The maximum rate at which a soil or roc' is capable of absorbing

water or limiting infiltration.


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112. ,nfiltration rate- The rate at which a soil or roc' under specified conditions absorbs

falling rain, melting snow, or surface water expressed in depth of water per unit time.

characteristic describing the maximum rate at which water can enter the soil or roc', under

specified conditions, including the presence of an excess of water. t has the dimensions of

velocity

113. ,nection well- 6ell used for in0ecting fluids into the subsurface. well into which

fluids are being in0ected.

11$. ,nection .one- geological =formation,= group of formations, or 9art of a formation

receiving fluids through a well.

11#. ,n-situ density- The density of water measured at its actual depth.

11!. ,nterception- The process by which precipitation is caught and held by foliage, twigs,

and branches of trees, shrubs, and other vegetation, and lost by evaporation, never reaching

the surface of the ground. nterception equals precipitation on the vegetation minus

streamflow and through fall.

11(. ,nterface- The contact one between two materials of different chemical or physical

composition.

11". ,ntermittent tream- stream that flows periodically. 5ompare perennial stream.

11. ,nterstice - n opening in a roc' or soil that is not occupied by solid matter. n opening

or space which may be occupied by air, water, or other gaseous or liquid material.


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12%. ,rrigation return flow - The part of artificially applied water that is not consumed by

evapotranspiration and that migrates to an aquifer or surface water body.

121. ,sotropic mass - mass having the same property or properties in all directions.

122. ,sotropy- The condition in which the property or properties of interest are the same in all

directions.

123. /aminar flow - 7low in which the head loss is proportional to the first power of the

velocity.

12$. /eachate- 8aterials removed by the process of leaching. liquid that has percolated

through soil, roc' or waste and has extracted dissolved or suspended materials.

12#. /eaching- The removal of materials in solution from soil, roc', or waste. 4eparation or

dissolving out of soluble constituents from a porous medium by percolation of water.

12!. /eakage- The flow of water from one hydrogeologic unit to another. The lea'age may

be natural, as through semi-impervious confining layer, or human-made, as through an

uncased well. The natural loss of water from artificial structures as a result of hydrostatic

pressure.

12(. /osing stream- stream or reach of a stream in which water flows from the stream bed

into the ground.

12". /ysimeter- device for measuring percolation and leaching losses from a column of

soil under controlled conditions.


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12. 0atric potential- The energy required to extract water from a porous medium to

overcome the capillary and adsorptive forces.

13%. 0echanical dispersion- The process whereby solutes are mechanically mixed during

advective transport caused by the velocity variations at the microscopic level.

131. 0iscible displacement- The mutual mixing and movement of two fluids that are soluble

in each other.

132. 0odel- conceptual, mathematical, or physical system obeying certain specified

conditions, whose behavior is used to understand the physical system to which it is analogous

in some way.

133. 0oisture content - The ratio, expressed as a percentage, of either )a* the weight of water

to the weight of solid particles expressed as moisture weight percentage or )b* the volume of

water to the volume of solid particles expressed as moisture volume percentage in a given

volume of porous medium.

13$. 0oisture equivalent - The percentage of water retained in a soil sample 1 cm thic' after

it has been saturated and sub0ected to a centrifugal force 1%%% times gravity for 3% minutes.

5entrifuge moisture equivalent is the water content of a soil after it has been saturated with

water and then sub0ected for 1 hour to a force equal to 1%%% times that of gravity.

13#. 0oisture tension - The equivalent negative pressure of water in an unsaturated porous

medium equal to the pressure that must be applied to the medium to bring the water to


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hydraulic equilibrium through a porous permeable material with a pool of water of the same

composition.

13!. 0oisture volume percentage - The ratio of the volume of water in a soil to the total bul'

volume of the soil.

13(. 0oisture weight percentage - The moisture content expressed as a percentage of the

oven-dry weight of a soil.

13". 0olecular diffusion - The process whereby solutes are transported at the microscopic

level due to variations in the solute concentrations within the fluid phases.

13. 1onpoint source - ny source, other than a point source, which discharges pollutants

into air or water. 4ource originating over broad areas, such as areas of fertilier and pesticide

application and lea'ing sewer systems, rather than from discrete points.1$%. 2ne +undred 3ear Flood !>ne :ercent 5hance 7lood* - 7lood magnitude that has one

chance in 1%% of being exceeded in any future 1-year period. The occurrence of floods is

assumed to be random in time, or regularity of occurrence is implied. The exceeding of a 1-

percent chance is no guarantee, therefore, that a similar sie flood will not occur next wee'.1$1. )articulate transport - The movement of particles in subsurface water.

1$2. )artitioning function - mathematical relation describing the distribution of a reactive

solute between solution and other phases.

1$3. )eclet number- relationship between the advective and diffusive components of

solute transport expressed as the ratio of the product of the average interstitial velocity, times

the characteristic length, divided by the coefficient of molecular diffusion/ small values

indicate diffusion dominance, large values indicate advection dominance.

1$$. )ercent saturation- The ratio, expressed as a percentage, of )a* the volume of water to

)b* the total volume of intergranular space )voids* in a given porous medium.


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1$#. )erched groundwater- ?roundwater separated from an underlying body of

groundwater by an unsaturated one. @nconfined groundwater separated from an underlying

body of ground water by an unsaturated one. ts water table is a perched water table.

:erched groundwater is held up by a perching bed whose permeability is so low that water

percolating downward through it is not able to bring water in the underlying unsaturated one

above atmospheric pressure.

1$!. )ellicular water- The film of water left around each grain or fracture surface of water-

bearing material after gravity drainage. 6ater that can be extracted by root absorption and

evaporation but cannot be moved by gravity or by the unbalanced film forces resulting from

localied evaporation and transpiration.

1$(. )ercolation& The downward movement of water through the unsaturated one. The

downward flow of water in saturated or nearly saturated porous medium at hydraulic

gradients of the order of 1.% or less.

1$". )erennial tream- stream that flows all year round. 5ompare intermittent stream.

1$. )ermeability- The property of a porous medium to transmit fluids under a hydraulic

gradient.

1#%. )ermeability coefficient- The rate of flow of water through a unit cross-sectional area

under a unit hydraulic gradient at the prevailing temperature )field permeability coefficient*

or ad0usted to a temperature of 1#%5.

1#1. )ie.ometer- devise used to measure groundwater pressure head at a point in the

subsurface.

1#2. )oint source- ny discernible, confined, or discrete conveyance from which pollutants

are or may be discharged, including, but not limited to, any pipe, ditch, channel, tunnel,

conduit, well, container, rolling stoc', concentrated animal feeding operation, or vessel or

other floating craft.


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1#3. )ollution- 4pecific impairment of water quality by agricultural, domestic, or industrial

wastes )including thermal and atomic wastes*, to a degree that has an adverse effect upon any

beneficial use of water.

1#$. )ore space - The total space not occupied by solid soil or roc' particles.

1##. )orosity- The ratio, usually expressed as a percentage, of the total volume of voids of a

given porous medium to the total volume of the porous medium.

1#!. )otable water - 6ater that is suitable for human consumption.

1#(. )otential- ny of several different scalar quantities, each of which involves energy as a

function of position or of condition/ e.g. the fluid potential of groundwater.

1#". )otential drop - The difference in total head between two equipotential lines.

1#. )otentiometric surface - n imaginary surface representing the static head of

groundwater and defined by the level to which water will rise in a tightly cased well.

1!%. )ressure head -


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time, because of physical and chemical interactions between the radionuclide and the

geohydrologic unit through which the radionuclide travels.

1!3. Reaction path modeling- simulation approach to studying the chemical evolution of a

)natural* system.

1!$. Recharge- The process of addition of water to the saturated one/ also the water added.

1!#. Recharge area - n area in which water reaches the one of saturation by surface

infiltration.

1!!. Recharge capacity - The ability of the soils and underlying materials to allow

precipitation and runoff to infiltrate and reach the one of saturation.

1!(. Retardation factor - The ratio of the average linear velocity of groundwater to the

velocity of the retarded constituent at 5+5oA%.#.

1!". Runoff- That part of precipitation that flows toward the streams on the surface of the

ground or within the ground. unoff is composed of baseflow and surface runoff.

1!. aline water - 6ater that generally is considered unsuitable for human consumption or

for irrigation because of its high content of dissolved solids. 5ommonly expressed as

milligrams per liter )mg+;* of dissolved solids, with 3#,%%% mg+; defined as equivalent to sea

water, slightly saline as 1,%%% - 3,%%% mg+;, moderately saline as 3,%%% - 1%,%%% mg+;, very

saline as 1%,%%% - 3#,%%% mg+;, and brine has more than 3#,%%% mg+;.

1(%. altwater intrusion - The movement of salt water into fresh water aquifers.


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1(1. aturated .one - Those parts of the earths crust in which all voids are filled with water

under pressure greater than atmospheric.

1(2. eep - n area, generally small, where water or oil percolates slowly to the land surface.

To move slowly through small openings of a porous material.

1(3. eepage- The fluid discharged at a seep. The amount of fluid discharged at a seep.

45#% eepage face - boundary between the saturated flow field and the atmosphere along

which groundwater discharges, either by evaporation or movement =downhill= along the land

surface or in a well as a thin film in response to the force of gravity.

1(#. eepage line - The uppermost level at which flowing water emerges along a seepage

face. The upper free water surface of the one of seepage.

1(!. heet Flow- 7low that occurs overland in places where there are no defined channels,

spreading out over the surface at uniform depth.

1((.

1(". ite characteri.ation - general term applied to the investigation activities at a specific

location that examines natural phenomena and human-induced conditions important to the

resolution of environmental, safety and water-resource issues.

1(. oil bulk density - The mass of dry soil per unit bul' soil.

1"%. oil moisture- 4ubsurface liquid water in the unsaturated one expressed as a fraction of

the total porous medium volume occupied by water.


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1"1. olubility- The total amount of solute species that will remain indefinitely in a solution

maintained at constant temperature and pressure in contact with the solid crystals from which

the solutes were derived.

1"2. olute transport - The net flux of solute through a hydrogeologic unit controlled by the

flow of subsurface water and transport mechanisms.

1"3. olution - homogeneous mixture of two or more components. n ideal solutions, the

movement of molecules in charged species are independent of each other. n aqueous

solutions charged species interact even at very low concentrations, decreasing the activity of

the solutes.

1"$. orption- general term used to encompass the process of absorption and adsorption.

1"#. tormwater &ischarge- :recipitation that does not infiltrate into the ground or

evaporate due to impervious land surfaces but instead flows onto ad0acent land or water areas

and is routed into drain+sewer systems.

46$% ubsurface Flow- The lateral motion of water through the upper layers of the ground

until it enters a stream channel.

1"(.

1"". ubsurface water- ll water that occurs below the land surface.

1". ubirrigation- rrigation of plants with water delivered to the roots from underneath.

6ith respect to alluvial valley floors, the supplying of water to plants from underneath or


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from a semi-saturated or saturated subsurface one where water is available for use by

vegetation.

1%. urface Runoff- The runoff that travels overland to the stream channel. ain that falls

on the stream channel is often lumped with this quantity.

11. 7ensiometer- device used to measure the moisture tension in the unsaturated one.

12. 7otal soil-water potential- The sum of the energy-related components of a soil-water

system/ i.e., the sum of the gravitational, matric, and osmotic components.

13. 7ransient- pulse dampened oscillation or other temporary phenomena occurring in a

system prior to reaching a steady-state condition.

1$. 7ransmissivity- The rate at which water of the prevailing 'inematic viscosity is

transmitted through a unit width of the aquifer under a unit hydraulic gradient. t is equal to

an integration of the hydraulic conductivities across the saturated part of the aquifer

perpendicular to the flow paths.

1#. 7ranspiration- 6ater discharged into the atmosphere from plant surfaces.

1!. 7ransport - 5onveyance of solutes and particulates in flow systems.

1(. 7urbulent flow - The flow condition in which inertial forces predominate over viscous

forces and in which head loss is not linearly related to velocity.

1". 8nconfined - condition in which the upper surface of the one of saturation forms a

water table under atmospheric pressure.


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1. 8nconfined aquifer - n aquifer which has a water table.

2%%. 8nsaturated flow - The movement of water in a porous medium in which the pore

spaces are not filled to capacity with water.

2%1. 8nsaturated .one - The one between the land surface and the water table. The one

between the land surface and the deepest water table which includes the capillary fringe.

6ater in this one is generally under less than atmospheric pressure, and some of the voids

may contain air or other gases at atmospheric pressure. Beneath flooded areas or in perched

water bodies the water pressure locally may be greater than atmospheric.

2%2. 8pconing- :rocess by which saline water underlying freshwater in an aquifer rises

upward into the freshwater one as a result of pumping water from the freshwater one.

2%3. 9oid ratio - The ratio of )a* the volume of void space to )b* the volume of solid particles

in a given soil mass.

2%$. 9olatiles- 4ubstances with relatively large vapor pressures. 8any organic substances are

almost insoluble in water so that they occur primarily in a gas phase in contact with water,

even though their vapor pressure may be very small.

2%#. :ater content - The amount of water lost from the soil after drying it to constant weight

at 1%#%5, expressed either as the weight of water per unit weight of dry soil or as the volume

of water per unit bul' volume of soil.

2%!. :atershed- The land area from which water drains toward a specific point in a natural

basin such as a watercourse or water body.


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2%(. :ater table - The upper surface of a one of saturation except where that surface is

formed by a confining unit. The upper surface of the one of saturation on which the water

pressure in the porous medium equals atmospheric pressure.

2%". :ell - bored, drilled or driven shaft, or a dug hole, whose depth is greater than the

largest surface dimension.

2%. :ell efficiency- the ratio of the drawdown in the formation ad0acent to the well divided

by the drawdown in the well.

21%. :ell inection - The subsurface emplacement of =fluids= through a bored, drilled, or

driven =well=, or through a dug well, where the depth of the dug well is greater than the

largest surface dimension.

211. :ell log& an accurately record made during or after drilling that shows the value of

various parameters )e.g., formation thic'ness, well diameter, fractures, geophysical

properties, geochemical data, or flow data* with depth in the well.212. :ell loss- the drop in hydraulic head in a well bore below that in the ad0acent aquifer or

reservoir created by turbulent flow and by frictional head losses in the well screen and in the

gravel pac'.

213. :ell point- a portion of a casing that is screened and near the bottom of the well. 4ome

actually have conical points )drive points* on the bottom that are used when driving a well by

hand. 6ell point systems are commonly used in shallow dewatering pro0ects.

21$. :ell screen- a portion of a well casing that is perforated or slotted to allow water to

pass.

21#. :ilting point- the soil moisture below which a type of plant can no longer extract water

from the soil. The plant then suffers turgor loss )it wilts*.

21!. ;erophyte- a plant that thrives in arid or semiarid conditions.


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21(. 3oung

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HYDROLOGIC TERMS