A water well system next to a house, showing how aquifers are an important source of water. Groundwater is the word used to describe precipitation that has infiltrated the soil beyond the surface and collected in empty spaces underground. There are two general types of aquifers: confined and unconfined. Confined aquifers have a layer of impenetrable rock or clay above them, while unconfined aquifers lie below a permeable layer of soil.
Many different types of sediments and rocks can form aquifers, including gravel, sandstone, conglomerates, and fractured limestone. Aquifers are sometimes categorized according to the type of rock or sediments of which they are composed. A common misconception about aquifers is that they are underground rivers or lakes. While groundwater can seep into or out of aquifers due to their porous nature, it cannot move fast enough to flow like a river. Much of the water we use for domestic, industrial, or agricultural purposes is groundwater.
Most groundwater, including a significant amount of our drinking water, comes from aquifers. In order to access this water, a well must be created by drilling a hole that reaches the aquifer.
While wells are manmade points of discharge for aquifers, they also discharge naturally at springs and in wetlands. This infographic provides facts and illustrations to explain the process. This infographic is part of a four-part educational series on Ground Water. Search-Icon Created with Sketch. KQED is a proud member of. Always free. Sign In. KQED Inform. Save Article Save Article. How Does an Aquifer Work? An aquifer is filled with moving water and the amount of water in storage in the aquifer can vary from season to season and year to year.
Ground water may flow through an aquifer at a rate of 50 feet per year or 50 inches per century, depending on the permeability. But no matter how fast or slow, water will eventually discharge or leave an aquifer and must be replaced by new water to replenish or recharge the aquifer. Thus, every aquifer has a recharge zone or zones and a discharge zone or zones. Figure 2 is a simple cartoon showing three different types of aquifers: confined, unconfined, and perched. Recharge zones are typically at higher altitudes but can occur wherever water enters an aquifer, such as from rain, snowmelt, river and reservoir leakage, or from irrigation.
Discharge zones can occur anywhere; in the diagram, discharge occurs not only in springs near the stream and in wetlands at low altitude, and also from wells and high-altitude springs. The amount of water in storage in an aquifer is reflected in the elevation of its water table. If the rate of recharge is less than the natural discharge rate plus well production, the water table will decline and the aquifer's storage will decrease.
A perched aquifer's water table is usually highly sensitive to the amount of seasonal recharge so a perched aquifer typically can go dry in summers or during drought years. Why is Groundwater So Clean? Aquifers are natural filters that trap sediment and other particles like bacteria and provide natural purification of the ground water flowing through them. Header link June 22, Read more. Header link September 15, Header link November 3, Header link May 15, Water Education Foundation.
Aquapedia background January 30, Aquifers Overview Aquifers play an important role as a source of freshwater for urban areas and agricultural irrigation. Aquifer Challenges Surging demand for water, and such related practices as overdrafting , have burdened aquifers and connected ecosystems in recent decades. Referring Pages. Share this page. Related Links. Footer pod May 20,
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