– a general
term for detrital deposits made by streams on river beds, flood plains, and
alluvial fans, especially a deposit of silt or silty clay laid down during a
time of flood.
Anisotropy – The
condition of having different properties in different directions.
Properties that are dependent upon direction are said to be anisotropic.
Aquifer – A 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.
Area of influence –
the area throughout which water levels decline measurably because of
discharge from a well. Theoretically, the effects of pumping extend to the
boundary of the aquifer.
– That part
of stream discharge derived from groundwater seeping into the stream.
Basin – The drainage
area of a stream, includes both surface and ground water drainage.
Clay – a detrital
mineral particle having a diameter less than 1/256 mm (4 microns).
That portion of the precipitation returned to the air through evaporation
Fluvial – of or
pertaining to rivers, produced by the action of a stream or river.
Formation – a
formation is a regionally extensive mappable geologic unit with reasonably
constant lithology; an aquifer may comprise one or more formations or may
consist of particular high-conductivity beds within a formation.
Glacial – pertaining
to the activities of glaciers, or to the features or materials produced
Gravel – rounded
fragments with diameters in the range 4.76 to 76 mm (3 in.), more loosely,
an unconsolidated natural accumulation of rounded rock fragments, mostly of
particles larger than sand (diameter greater than 2 mm), such as boulders,
cobbles, pebbles, granules, or any combination of these.
Ground water – That
part of the subsurface water that is in the zone of saturation.
Ground water divide –
a ridge in the water table, from which ground water moves away in both
– The hydraulic conductivity of a medium is the volume of water at the
existing kinematic 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.
Hydrologic cycle – The
constant circulation of water from the sea through the atmosphere, to the
land, and its eventual return to the atmosphere by way of transpiration and
evaporation from the land and evaporation fro the sea.
gradient – The slope of the potentiometric surface, which is an imaginary
surface representing the total head of ground water and defined by the level
to which water will rise in a well. The water table is a particular
Residence time – The
average length of time a substance spends in given reservoir that is at a
steady stare with respect to the processes that add and remove the substance
to and from the reservoir. Residence time is calculated as the ratio of the
reservoir size to the rate of inflow or outflow (which are equal at steady
Sand – a detrital
particle smaller than a granule and larger than a silt grain, having a
diameter in the range of 1/16 to 2 mm.
Silt – A detrital
particle finer than fine sand and coarser than clay, commonly in the range
1/16 to 1/256 mm.
Soil moisture – The
water contained in the unsaturated zone.
The rate of discharge of water from the well divided by drawdown of water
level within the well. Specific capacity decreases with duration of
ratio of volume of water yielded from water-bearing material by gravity
drainage, as occurs when the water table declines, to the volume of
glaciofluvial, glaciolacustrine, or glaciomarine drift, consisting of sorted
and layered material deposited by a meltwater stream or settled from
suspension in a body of quiet water adjoining a glacier.
Streamflow depletion –
The reduction of streamflow caused by pumping due to either induced
infiltration or the capture of ground water that would have reached the
stream if the pumping had not diverted it to the well.
Till – Unstratified
drift, deposited directly by a glacier without reworking by meltwater,
consisting of a mixture of clay, silt, sand, gravel, and boulders ranging
widely in shape and size.
Transmissivity – The
rate at which water at the prevailing kinematic viscosity is transmitted
through a unit width of the aquifer under a unit hydraulic gradient.
material – A sediment that is loosely arranged or unstratified or whose
particles are not cemented together, occurring either at the surface or at
Zone of saturation – a
subsurface zone in which all the interstices are filled with water under
pressure greater than that of the atmosphere. The water table is the top of
the zone of saturation.