The area which the potentiometric surface is lowered by withdrawal or raised by injection, of water through a well.
A geologic unit that is saturated and sufficiently permeable to transmit significant economic quantities of water to wells and springs.
The lowest part of the zone of aeration, immediately above the water table, where water is under pressure that is less than atmospheric pressure.
An aquifer overlain by a confining layer of low permeability.
Water trapped in the pores of a sedimentary rock at the time of deposition; fossil water.
A unit of intrinsic permeability = 9.87 x 10-9cm2
The basic equation describing ground water flow put forth by Darcy: Q = KiA
An area where subsurface water is discharged to land, bodies of water, or the atmosphere.
Effective Porosity (nc)
The percentage of the total volume of a soil or rock that consists of interconnected pore space. The term is sometimes used analogously to specific yield.
The quantity of water held by the soil or rock against the pull of gravity. Field capacity is dependent on the length of time the soil or rock has been undergoing gravity drainage, while specific retention is not.
Two-dimensional representation of flow lines and equipotentials.
A measure of the potential energy of a fluid at any given point with respect to a given datum. In practice, it is the elevation to which water rises at a given point as a result of reservoir pressure.
Hydraulic Conductivity (K)
The capacity of porous medium to transmit water. The rate at which fluid can move through a permeable medium depends on the properties of the fluid (viscosity and specific weight) and properties of the medium (intrinsic permeability).
Hydraulic Gradient (i)
Rate of change in total head per unit of distance of flow in a given direction.
Intrinsic Permeability (ki)
A property of the porous medium that measures the relative ease with which a fluid can be transmitted through it under a hydraulic gradient. It is dependent upon the pore size and is measured in darcys.
Water that is derived directly from magma and is thought to have come to the earth's surface for the first time.
A unit of hydraulic conductivity in gpd/ft2. Rate of flow in gallons per day through a cross section of 1 square foot under a unit hydraulic gradient at 60 deg F.
Perched Ground Water
Unconfined ground water separated from an underlying body of ground water by an unsaturated zone.
The property of a porous rock or soil for transmitting a fluid. It measures the relative ease of flow under unequal pressure.
The percentage of the bulk volume of a rock or soil that is occupied by void space.
A surface that represents the total head of groundwater and is defined by the level to which water will rise in a well.
An area where water infiltrates downward into the saturated zone.
That part of precipitation appearing in surface streams.
Specific Retention (Sr)
Ratio of the volume of water a soil or rock can retain against gravity drainage to the total volume of the soil or rock, usually stated as a percentage.
Specific Storage (Ss)
Amount of water per unit volume of a saturated formation that is stored or expelled from storage due to compressibility of mineral skeleton and pore water per unit change in head. Units are 1/ft.
Specific Yield (Sy)
Ratio of the volume of water that drains from a saturated soil or rock due to gravity to the total volume of soil or rock, stated as a percentage.
Storativity or Storage Coefficient
Volume of water that a permeable unit releases from or takes into storage per unit surface area of the aquifer per unit change in head. In an unconfined aquifer, storage = specific yield.
The capacity of an aquifer to transmit water of the prevailing kinematic viscosity. T = Kb, where b = saturated thickness of the aquifer. Dimensions are gpd/ft or ft2/day
An aquifer having a water table.
Ground water that flows beneath the bed or alluvial plain of a surface stream, especially in arid regions.
Vadose zone or zone of aeration
A subsurface zone containing water under pressure that is less than atmospheric pressure.
The surface within unconfined groundwater at which the hydraulic pressure is equal to atmospheric pressure.
The region drained by a stream or body of water, or a drainage divide.