Everything about Groundwater totally explained
Groundwater is
water located beneath the
ground surface in
soil pore spaces and in the
fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an
aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the
water table. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at
springs and
seeps, streams and can form
oases or
wetlands. Groundwater is also often withdrawn for
agricultural,
municipal and
industrial use by constructing and operating extraction
wells. The study of the distribution and movement of groundwater is
hydrogeology, also called groundwater
hydrology.
Typically, groundwater is thought of as liquid water flowing through shallow aquifers, but technically it can also include
soil moisture,
permafrost (frozen soil), immobile water in very low permeability bedrock, and deep
geothermal or
oil formation water. Groundwater is hypothesized to provide
lubrication that can possibly influence the movement of
faults. It is likely that much of the Earth's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to the Earth. The formation of some of the landforms observed on
Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of
Jupiter's moon
Europa.
Aquifers
An
aquifer is a layer of relatively porous substrate that contains and transmits groundwater. When water can flow directly between the surface and the saturated zone of an aquifer, the aquifer is unconfined. Because water tends to flow downward due to gravity, the deeper parts of unconfined aquifers are usually more saturated with groundwater.
The upper level of this saturated layer of an unconfined aquifer is called the
water table or phreatic surface. Below the
water table, where generally all pore spaces are saturated with water is the
phreatic zone.
Substrate with relatively low porosity that permits limited transmission of groundwater is known as an aquitard. An aquiclude is a substrate with porosity that's so low it's virtually impermeable to groundwater.
A confined aquifer is an aquifer that's overlain by a relatively impermeable layer of rock or substrate such as an aquiclude or aquitard. If a confined aquifer follows a downward grade from its
recharge zone, groundwater can become pressurized as it flows. This can create
artesian wells that flow freely without the need of a pump or rise to a higher elevation than the static
water table at the above, unconfined aquifer.
The characteristics of aquifers vary with the geology and structure of the substrate and topography in which they occur. Generally, the more productive and useful aquifers occur in sedimentary geologic formations. By comparison, weathered and fractured crystalline rocks yield relatively smaller quantities of groundwater in many environments. Unconsolidated to poorly cemented alluvial materials that have accumulated as valley-filling sediments in major river valleys and geologically subsiding structural basins are included among the most productive sources of groundwater.
The high
specific heat capacity of water and the insulating effect of soil and rock can mitigate the effects of climate and maintain groundwater at a relatively steady temperature. In some places where groundwater temperatures are maintained by this effect at about 50°F/10°C, groundwater can be used for controlling the temperature inside structures at the surface. For example, during hot weather relatively cool groundwater can be pumped through radiators in a home and then returned to the ground in another well. During cold seasons, because it's relatively warm, the water can be used in the same way as a source of heat for
heat pumps that's much more efficient than using air. The relatively constant temperature of groundwater can also be used for
heat pumps.
Further Information
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