An aquifer refers to any underground layers of bearing rocks or geological rocks that yield sufficient groundwater for springs and wells. According to Geological terms, an aquifer could be referred to as a body of saturated rocks or geological formation through which water can be easily moved into the wells or streams. The top of the water level in an aquifer is known as the water table.
An aquifer gets filled with water from rain or melted snow that drains into the ground. In some areas, water passes through the soil of the aquifer while in other areas it enters through joints and cracks in rocks where it moves downwards until it reaches the rocks that are less preamble.
Aquifers are generally referred to as reservoirs and can easily dry up when people drain them faster than they have refilled by nature. Aquifers must not only be preamble but also be porous and are found in rock types such as sandstone, conglomerate, fractured limestone, and unconsolidated sand, gravels, and fractured volcanic rocks.
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Types of Aquifer
There are two types of aquifers namely confined aquifer and unconfined aquifer.
Let Us Discuss Each Type of Aquifer in Detail.
Confined aquifers are defined as the preamble rock units that are usually deeper under the ground than the unconfined aquifers. They are wrapped by relatively impermeable rocks or clay that limit groundwater movements into or out of the confined aquifers. The groundwater in confined aquifers is under pressure and will rise inside a borehole drilled into an aquifer. The level to which water level rises is known as potentiometric surface. An artesian flow is where the water flows out of the borehole under natural pressure.
Confined aquifers may be replenished or recharged by rain or stream water infiltrating the rocks at some considerable distance away from the confined aquifers. The groundwater in the confined aquifers may be a thousand years old.
Semi Confined Aquifers
A semi-confined aquifer, also known as the leaky aquifer is an aquifer whose upper and lower boundaries are aquitards (an aquitard is a zone within the Earth that restricts the groundwater from one aquifer to another), or whose one boundary is aquitards and another is aquiclude ( an aquiclude is a geological formation that absorbs and hold water but does not transmit it at a sufficient rate to supply to a spring, wells, etc.)
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Unconfined Aquifer (Water Table Aquifers)
Unconfined aquifers are sometimes known as water table aquifers or phreatic aquifers because the upper boundary of an unconfined aquifer is a water table or phreatic surface. When the groundwater is in direct contact with the atmosphere through the direct pores spaces of overlying rock or soil, then the aquifer is said to be an unconfined aquifer. The depth to the water table in unconfined aquifers varies according to the topography, geology, season and tidal effects, and the quantities of water being pumped from the aquifer.
A natural aquifer is a body of saturated rock through which water can easily move. Natural aquifers may be both porous and permeable and include rock types such as sandstone, conglomerate, fractured limestone, unconsolidated sand, or gravel. Fractured aquifers such as columnar basalt make the best aquifers. The rubble zones between the volcanic flows are both permeable and porous and make excellent purifiers. In an attempt to make wells productive, they must be drilled into an aquifer. Rock such as granite and schist are considered poor aquifers because they have a low preamble. However, if these rocks are highly fractured, they make the best aquifers.
A well is a hole drilled into the ground to penetrate an aquifer. Generally, such water must be pumped to the surface. If the water in the well is pumped faster than it is replenished, the water table is lower and may also go dry. When the water is pumped from a well, the water level is lowered into the cone of depression at the well.
Did You Know?
Groundwater may flow through an aquifer at a rate of 50 feet per year or 50 inches per century, depending on the permeability.
The high plain aquifer is considered an unconfined aquifer. Although it is shallow, it supplies 30% of the groundwater used for irrigation as well as providing drinking water to 2.3 million people.
Fine-grained rocks such as sandstone make the best aquifer.
The Ogallala, also known as the High plain aquifer makes one of the largest underground freshwater resources in the world
The groundwater contained in the aquifers is one of the most important sources of water on Earth. As per the National Oceanic and Atmospheric Administration, about 30% of our liquid freshwater is groundwater.