Science of Water : Concepts and Applications

24 The Science of Water: Concepts and Applications
have a quality problem. If we do not have an adequate supply of quality water, we have a quantity
problem.
In this section, the focus is on surface water and groundwater hydrology and the mechanical
components associated with collection and conveyance of water from its source to the public water
supply system for treatment. Well supplies are also discussed.
KEY DEFINITIONS
Annular space The space between the casing and the wall of the hole.
Aquifer A porous, water-bearing geologic formation.
Caisson Large pipe placed in a vertical position.
Cone of depression As the water in a well is drawn down, the water near the well drains or
fl ows into it. The water will drain further back from the top of the water table into the
well as drawdown increases.
Confi ned aquifer An aquifer that is surrounded by formations of less permeable or impermeable
material.
Contamination The introduction into water of toxic materials, bacteria, or other deleterious
agents that make the water unfi t for its intended use.
Drainage basin An area from which surface runoff or groundwater recharge is carried into a
single drainage system. It is also called catchment area, watershed, and drainage area.
Drawdown The distance or difference between the static level and the pumping level. When the
drawdown for any particular capacity well and rate pump bowls is determined, the pumping
level is known for that capacity. The pump bowls are located below the pumping level
so that they will always be underwater. When the drawdown is fi xed or remains steady,
the well is then furnishing the same amount of water as is being pumped.
Groundwater Subsurface water occupying a saturated geological formation from which wells
and springs are fed.
Hydrology The applied science pertaining to properties, distribution, and behavior of water.
Impermeable A material or substance that water will not pass through.
Overland fl ow The movement of water on and just under the Earth’s surface.
Permeable A material or substance that water can pass through.
Porosity The ratio of pore space to total volume. That portion of a cubic foot of soil that is air
space and could therefore contain moisture.
Precipitation The process by which atmospheric moisture is discharged onto the Earth’s crust.
Precipitation takes the form of rain, snow, hail, and sleet.
Pumping level The level at which the water stands when the pump is operating.
Radius of infl uence The distance from the well to the edge of the cone of depression, the radius
of a circle around the well from which water fl ows into the well.
Raw water The untreated water to be used after treatment as drinking water.
Recharge area An area from which precipitation fl ows into underground water sources.
Specifi c yield The geologist’s method for determining the capacity of a given well and the production
of a given water-bearing formation. It is expressed as gal/min/ft of drawdown.
Spring A surface feature where without the help of man, water issues from rock or soil onto the
land or into a body of water, the place of issuance being relatively restricted in size.
Static level The height to which the water will rise in the well when the pump is not operating.
Surface runoff The amount of rainfall that passes over the surface of the Earth.
Surface water The water on the Earth’s surface as distinguished from water underground
(groundwater).
Unconfi ned aquifer An aquifer that sits on an impervious layer, but is open on the top to local
infi ltration. The recharge for an unconfi ned aquifer is local. It is also called a water table
aquifer.