An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials. Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteristics. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology. Related terms include aquitard, which is a bed of low permeability along an aquifer, and aquiclude, which is a solid, impermeable area underlying or overlying an aquifer, the pressure of which could create a confined aquifer. The classification of aquifers is as follows: Saturated versus unsaturated; aquifers versus aquitards; confined versus unconfined; isotropic versus anisotropic; porous, karst, or fractured; transboundary aquifer.
The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated.
Water extraction is the process of taking water from any source, either temporarily or permanently, for flood control or to obtain water for, for example, irrigation. The extracted water could also be used as drinking water after suitable treatment.
Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. 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 the surface; it may discharge from the surface naturally at springs and seeps, 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 Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells.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.
Fongafale is the largest of Funafuti's islets in Tuvalu. It is a long narrow sliver of land, 12 kilometres long and between 10 and 400 metres wide, with the South Pacific Ocean and reef on the east and the protected lagoon on the west. The north part is the Tengako peninsula, and Funafuti International Airport runs from northeast to southwest on the widest part of the island, with the village and administrative centre of Vaiaku on the lagoon side.
Saltwater intrusion is the movement of saline water into freshwater aquifers, which can lead to groundwater quality degradation, including drinking water sources, and other consequences. Saltwater intrusion can naturally occur in coastal aquifers, owing to the hydraulic connection between groundwater and seawater. Because saline water has a higher mineral content than freshwater, it is denser and has a higher water pressure. As a result, saltwater can push inland beneath the freshwater. In other topologies, submarine groundwater discharge can push fresh water into saltwater.
Fossil water or paleowater is an ancient body of water that has been contained in some undisturbed space, typically groundwater in an aquifer, for millennia. Other types of fossil water can include subglacial lakes, such as Antarctica's Lake Vostok, and even ancient water on other planets.
Used in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar to that used in heat transfer to describe the flow of heat in a solid. The steady-state flow of groundwater is described by a form of the Laplace equation, which is a form of potential flow and has analogs in numerous fields.
The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer's region. Additionally, the Edwards Aquifer feeds the Comal and San Marcos springs, provides springflow for recreational and downstream uses in the Nueces, San Antonio, Guadalupe, and San Marcos river basins, and is home to several unique and endangered species.
Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and, is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally and through anthropogenic processes, where rainwater and or reclaimed water is routed to the subsurface.
Submarine groundwater discharge (SGD) is a hydrological process which commonly occurs in coastal areas. It is described as submarine inflow of fresh-, and brackish groundwater from land into the sea. Submarine Groundwater Discharge is controlled by several forcing mechanisms, which cause a hydraulic gradient between land and sea. Considering the different regional settings the discharge occurs either as (1) a focused flow along fractures in karst and rocky areas, (2) a dispersed flow in soft sediments, or (3) a recirculation of seawater within marine sediments. Submarine Groundwater Discharge plays an important role in coastal biogeochemical processes and hydrological cycles such as the formation of offshore plankton blooms, hydrological cycles, and the release of nutrients, trace elements and gases. It affects coastal ecosystems and has been used as a freshwater resource by some local communities for millennia.
Surficial aquifers are shallow aquifers typically less than 50 feet (15 m) thick, but larger surficial aquifers of about 60 feet (18 m) have been mapped. They mostly consist of unconsolidated sand enclosed by layers of limestone, sandstone or clay and the water is commonly extracted for urban use. The aquifers are replenished by streams and from precipitation and can vary in volume considerably as the water table fluctuates. Being shallow, they are susceptible to contamination by fuel spills, industrial discharge, landfills, and saltwater. Parts of southeastern United States are dependent on surficial aquifers for their water supplies.
Overdrafting is the process of extracting groundwater beyond the equilibrium yield of the aquifer. Groundwater is the fresh water that can be found underground; it is also one of the largest sources. Groundwater depletion can be comparable to "money in a bank", The primary cause of groundwater depletion is pumping or the excessive pulling up of groundwater from underground aquifers.
Groundwater models are computer models of groundwater flow systems, and are used by hydrologists and hydrogeologists. Groundwater models are used to simulate and predict aquifer conditions.
A spreading ground is a water conservation facility that retains surface water long enough for it to percolate into the soil. Spreading grounds must be located where underlying soils are permeable and connected to a target aquifer. Locating them above silt or clay would prevent the surface water from reaching formations that store water.
Seawater intrusion is either caused by groundwater extraction or increased in sea level. For every 1 foot of freshwater depression, sea-salty waters rises 40 feet as the cone of depression forms. Salinization of groundwater is one of the main water pollution ever produced by mankind or from natural processes. It degrades water quality to the point it passes acceptable drink water and irrigation standards. To this day, the State of California enforced several methodologies through technical innovation and scientific approach to combat saltwater intrusion in areas vulnerable to saltwater intrusion.
Groundwater resources and occurrence in the Comoros Islands are variable owing to geological variability. Young volcanic islands, including the active Karthala volcano on Grande Comore, host two types of aquifers; a widespread basal aquifer characterised by deep groundwater table, high hydraulic conductivity, high recharge rate and saltwater intrusion issues in coastal areas, and local perched aquifer systems. Older, weathered volcanic islands such as Mayotte are characterised by more complex groundwater occurrence through discontinuous successions of perched aquifers. The Glorioso coral islands host a shallow freshwater lens fed by rainfall infiltration where freshwater-saltwater interactions and spatial patterns are strongly influenced by topography and evapotranspiration processes.
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include non-salty mineral-rich waters such as chalybeate springs. Fresh water may encompass frozen and meltwater in ice sheets, ice caps, glaciers, snowfields and icebergs, natural precipitations such as rainfall, snowfall, hail/sleet and graupel, and surface runoffs that form inland bodies of water such as wetlands, ponds, lakes, rivers, streams, as well as groundwater contained in aquifers, subterranean rivers and lakes. Fresh water is the water resource that is of the most and immediate use to humans.
The effects of climate change on the water cycle has important knock-on effects on the availability of freshwater resources, as well as other water reservoirs such as oceans, ice sheets, atmosphere and land surface. The water cycle is essential to life on earth and plays a large role in the global climate and the ocean circulation. The warming of the earth is expected to cause changes in the water cycle for various reasons. A warmer atmosphere can contain more water vapor which has effects on evaporation and rainfall. Oceans play a large role as well, since they absorb 93% of the increase in heat since 1971. This has effects on the water cycle and on human society, since the ocean warming directly leads to sea level rise.
Oceanic freshwater fluxes are defined as the transport of non saline water between the oceans and the other components of the Earth's system. These fluxes have an impact on the local ocean properties, as well as on the large scale circulation patterns.
