Aquifer

Aquifer

An aquifer is an underground layer of water-bearing permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Aquifers are critically important to both the environment and human society, as they are a major source of fresh water.

Types of Aquifers

Aquifers are categorized into two main types based on their porosity and permeability: confined and unconfined.

Confined Aquifer

A confined aquifer is bounded above and below by impermeable layers of rock or clay. The pressure in a confined aquifer generally exceeds atmospheric pressure, which can cause water to rise above the top of the aquifer when penetrated by a well—a condition known as artesian pressure.

Unconfined Aquifer

An unconfined aquifer, also known as a water-table or phreatic aquifer, is only bounded at the bottom by a relatively impermeable layer. The upper surface of this type of aquifer is the water table or phreatic surface.

Recharge Areas

Aquifers receive water from precipitation that percolates downward through the soil and rock in areas known as recharge areas. The rate of recharge is influenced by factors such as permeability of the surface soil, vegetation cover, and topography.

Aquifer Depletion

Aquifer depletion is a significant issue, particularly in areas of high agricultural or urban demand. Over-extraction can lead to a decrease in water levels, reduced water flow to surface water systems, land subsidence, and a reduction in water quality.

Management

Sustainable management of aquifer resources involves monitoring and regulating the rate of extraction to balance with the rate of recharge. Techniques such as artificial recharge, where water is intentionally added to an aquifer, are employed to help maintain aquifer levels.

Legal and Social Aspects

The legal framework governing the use of aquifer resources varies by jurisdiction but generally involves rights to use groundwater and obligations to avoid contaminating it. Social aspects include the role of aquifers in supporting livelihoods, particularly in agricultural communities, and in providing potable water.

See Also

• Water cycle
• Groundwater
• Hydrology
• Water conservation