A aquifer is an underground layer of permeable rock that holds water, rock cracks or un-consolidated material (gravel, sand, or silt). Groundwater can be extracted using well water. The study of the flow of water in aquifers and the characterization of aquifers is called hydrogeology. Related terms include orangitard , which is a low permeability bed along the aquifer, and aquiclude (or aquifuge ), which is a dense, watertight underlying area or lining the aquifer. If the impermeable area covers the aquifer, pressure may cause it to be a finite aquifer.
Video Aquifer
Depth
Aquifers can occur at various depths. Those closer to the surface are not only more likely to be used for water supply and irrigation, but also more likely to be filled by local rainfall. Many desert areas have limestone hills or mountains in them or close to those that can be utilized as ground water resources. Parts of the Atlas Mountains in North Africa, Lebanon and Anti-Lebanon range between Syria and Lebanon, Jebel Akhdar in Oman, part of the Sierra Nevada and adjacent ranges in the United States' Southwest, having a shallow aquifer exploited for their water. Over-exploitation can result in over-the-counter practical sustainable results; that is, more water is taken than it can be refilled. Along the coastline of certain countries, such as Libya and Israel, increased water use associated with population growth has led to a decrease in water levels and subsequent contamination of groundwater with saltwater from the sea.
The beach provides a model to help visualize the aquifer. If a hole is dug into the sand, very wet or saturated sand will be in shallow depth. This hole is a crude oil well, wet sand represents the aquifer, and the rate at which water rises in this hole represents the water table.
In 2013, large freshwater aquifers are found beneath the continental shelf off Australia, China, North America and South Africa. They contain about half a million cubic kilometers of "low salinity" water that can be economically processed into drinking water. Reserves are formed when sea levels are lower and rainwater flows to land on land that is not submerged until the ice age ended 20,000 years ago. The volume is estimated to be 100 times the amount of water extracted from other aquifers since 1900.
Maps Aquifer
Classification
This system shows two aquifers with a single (limited or impermeable) layer between them, surrounded by aquiclude rocks, which come into contact with rising currents (typical in humid areas). Water tables and unsaturated zones are also illustrated. An orangitard is a zone in the earth that limits the flow of groundwater from one aquifer to another. Aquitard sometimes, if completely watertight, is called aquiclude or aquifuge . Aquitard consists of layers of either clay or non-porous stones with low hydraulic conductivity.
Saturated compared to unsaturated
Groundwater can be found at almost any point beneath the surface of the earth that is superficial to some degree, although the aquifer does not always contain fresh water. The Earth's crust can be divided into two regions: saturated zone or phreatic zone (eg, aquifers, calculators, etc.), where all available space is filled with water, and zones unsaturated (also called vadose zone), where there is still a water bag containing water, but can be filled with more water.
Saturated means the water pressure is greater than the atmospheric pressure (has a measuring pressure & gt; 0). The definition of a water table is a surface where the pressure head is equal to the atmospheric pressure (where the measuring pressure is 0).
The unsaturated condition occurs above the water table where the pressure head is negative (absolute pressure can never be negative, but measuring pressure can) and incomplete water fills the pores of the aquifer ingredients in suction. The water content in the unsaturated zone is held in place by the strength of the surface adhesive and rises above the water table (isobar zero-measure-pressure) by capillary action to saturate the small zone above the phreatic surface (capillary fringe) less than atmospheric pressure. This is called voltage saturation and is not equal to saturation on the water base. The water content in the periphery of the capillaries decreases with increasing distance from the phreatic surface. The capillary head depends on the pore size of the soil. In sandy soil with larger pores, the head will be smaller than in clay with very small pores. The normal capillary rise in clay soil is less than 1.80 m (six feet) but can range between 0.3 and 10 m (one and 30 feet).
The increase in water capillaries in small diameter tubes involves the same physical process. The water table is the rate at which water will rise in a large diameter tube (for example, a well) that goes down into the aquifer and opens into the atmosphere.
Aquifer compared to i
Aquifers are typically saturated regions of subsurface that produce economically viable quantities of water to wells or springs (eg, sand and gravel or cracked rocks often make good aquifer materials).
Akuitar is a zone in the earth that limits the flow of ground water from one aquifer to another. The totally watertight guitar is called aquiclude or aquifuge . Aquitard consists of layers of clay or non-porous rock with low hydraulic conductivity.
In mountainous areas (or near rivers in mountain areas), the main aquifer is typically an unconsolidated alluvium, consisting mostly of horizontal layers of material stored by water processes (rivers and streams), which are cross-sectional (see a two-dimensional snippet of aquifers) appear as a coarse layer of coarse and fine material. Rough materials, because of the high energy required to move them, tend to be found nearer the source (the front or mountain stream), whereas fine-grained materials will make it farther from the source (to the flatter part of the basin or overbank area - sometimes called pressure areas ). Because there are fewer precipitate deposits near the source, this is the place where the aquifer is often unfettered (sometimes called the front), or in hydraulic communications with the soil surface.
Curbed compared indefinitely
There are two end members in the spectrum of aquifer types; limited and free (with semi-limited creatures in between). Uncontrollable aquifers are sometimes also called water surface or phreatic aquifers, because the upper limit is the water surface or the phreatic surface. (See Biscayne Aquifer.) Typically (but not always) a shallow aquifer at a particular location is unconstrained, meaning it has no limiting layer (aquitar or aquiclude) between it and the surface. The term "perch" refers to groundwater accumulating above a unit or layer with low permeability, such as a layer of clay. This term is commonly used to refer to small local groundwater areas that occur at higher altitudes of regional wide aquifer. The difference between aquifer perch and unbound is their size (smaller perch). A closed aquifer is an aquifer overlapped by a finite layer, often made of clay. The delimiter may offer some protection from surface contamination.
If the difference between finite and infinite is not geologically clear (ie, if it is unknown whether a clear boundary layer exists, or if the geology is more complex, for example, the aquifer cracked rocks), the return storativity value of the aquifer test can be used to determine it although the aquifer tests in the free aquifers must be interpreted differently from the finite ones). Closed aquifers have very low storativity values ​​(less than 0.01, and as little as 10 -5 ), meaning that aquifers store water using aquifer expansion mechanisms and water compressibility, which are usually very small. Unclassified aquifers have storativity (usually called specific results) greater than 0.01 (1% bulk volume); they release water from storage by a mechanism that completely drains the pores of the aquifer, releasing a relatively large amount of water (up to the drainage porosity of the aquifer material, or minimum volumetric water content).
Isotropic versus anisotropic
In an isotropic aquifer or aquifer layer, hydraulic conductivity (K) is the same for flow in all directions, while under anisotropic conditions it differs, especially in the horizontal (Kh) and vertical (Kv) sense.
A semi-finite aquifer with one or more acoustics works as anisotropic system, even when the separate layers are isotropic, since the values ​​of Kh and Kv compounds are different (see hydraulic transmisiveness and hydraulic resistance).
When calculating the flow into a water channel or flowing into a well in the aquifer, anisotropy must be taken into account so that the design resulting from the drainage system may be damaged.
Groundwater in rock formations
Groundwater may be in the underground river (eg caves where water flows freely underground). This may occur in eroded limestone areas known as karst topography, which forms only a small fraction of Earth's width. More common is that the pore space beneath the surface is saturated enough with water - like a kitchen sponge - that can be pumped out for agricultural, industrial or municipal use.
If rock units with low porosity are very cracked, it can also create a good aquifer (through flow gaps), provided the rock has sufficient hydraulic conductivity to facilitate the movement of water. Porosity is important, but, alone , it does not determine the ability of the stone to act as an aquifer. The area of ​​the Deccan Traps (basaltic lava) in western India is a good example of rock formations with high porosity but low permeability, which makes them a bad aquifer. Similarly, the Cretaceous Pore Group (Lime Top) of southeastern England, although having a fairly high porosity, has a low permeability of grains, with good water-yield characteristics largely due to micro-fracturing and fissuring.
Human dependence on groundwater
Most of the land area on Earth has some form of aquifers underlying them, sometimes at significant depths. In some cases, this aquifer is rapidly depleted by the human population.
Fresh water aquifers, especially those with limited infiltration by snow or rain, also known as meteoric water, can be over-exploited and dependent on local hydrogeology, may attract irreversible water or saltwater intrusion from hydraulically connected aquifers or surface water. corpses. This can be a serious problem, especially in coastal areas and other areas where the aquifer is pumping excessively. In some areas, groundwater may be contaminated by arsenic and other mineral toxins.
Aquifers are very important in human life and agriculture. The deep aquifers in dry areas have long been the source of water for irrigation (see Ogallala below). Many villages and even large cities withdraw their water supply from wells in the aquifers.
Urban water supply, irrigation, and industry are provided through large wells. Some wells for a single source of water supply are called "wellfields", which can draw water from a closed aquifer or not. Using groundwater from a deep and limited aquifer provides more protection from surface water contamination. Some wells, called "collector wells," are specifically designed to induce surface water infiltration (usually rivers).
Aquifers that provide sustainable fresh groundwater to urban areas and for agricultural irrigation are usually close to the ground (within a few hundred meters) and have some refills by fresh water. This refill is usually from rivers or meteoric water (sediment) that seeps into the aquifer through unsaturated matter.
Sometimes, sediment aquifers or "fossils" are used to provide irrigation and drinking water for urban areas. In Libya, for example, the Muammar Gaddafi Great River project has pumped large amounts of groundwater from the aquifers below the Sahara to densely populated areas near the coast. Although this has saved Libyan money over alternatives, desalination, the aquifers will dry within 60 to 100 years. The aquifer depletion has been cited as one of the causes of rising food prices in 2011.
Subsidence
In an unconsolidated aquifer, ground water is produced from the pore space between gravel particles, sand, and mud deposits. If the aquifer is limited by a low permeability layer, reduced water pressure in sand and gravel leads to slowing of water drainage from adjacent coatings. If this limited layer consists of compressed mud or clay, the loss of water to the aquifer reduces the water pressure in the finite layer, causing it to solidify from the weight of the coating geologic material. In severe cases, this compression can be observed on the soil surface as a decrease. Unfortunately, much of the decline in groundwater extraction is permanent (small elastic rebounds). Thus, the decline is not only permanent, but the compressed aquifer has a permanently reduced capacity to hold water.
Saltwater Intrusion
Aquifers near the coast have freshwater lenses near the surface and more densely populated seawater under freshwater. Sea water passes through aquifers that spread from the sea and are denser than fresh water. For porous (ie, sandy) aquifers near the coast, freshwater thickness over saltwater is about 12 meters (40 feet) for every 0.30 m (1 ft) freshwater head above sea level. This relationship is called the Ghyben-Herzberg equation. If too much ground water is pumped near the shore, salt water can infiltrate into a freshwater aquifer causing contamination of the drinkable freshwater supply. Many coastal aquifers, such as Biscayne Aquifer near Miami and the New Jersey Coastal Highlands aquifer, have problems with seawater intrusion as a result of excessive increases and sea level rise.
Copy
Aquifers in surface irrigation areas in semi-arid zones with the re-use of irrigation water losses that can not be avoided that seep underground with additional irrigation of well-risk salinity.
Surface irrigation water usually contains salt in the order of 0.5 g/l or more and the annual irrigation requirement is about 10,000 mÃ,³/ha or more so the annual salt import is about 5000 kg/ha or more.
Under the influence of continuous evaporation, the salt concentration of the aquifer water can increase continuously and ultimately lead to environmental problems.
For salinity control in such cases, each year a certain amount of drainage water will be discharged from the aquifer through a subsurface drainage system and discharged through a secure outlet. The drainage system may be horizontal (ie using pipes, tiles or trenches) or vertical (drainage by wells). To estimate drainage requirements, the use of groundwater models with agro-hydro-salinity components may be instrumental, eg SahysMod.
Example
The Great Artesian Basin located in Australia is the largest groundwater aquifer in the world (more than 1.7 million km²). It plays a big part in water supply for Queensland and the remote parts of South Australia.
The Guarani Aquifer, located beneath the surface of Argentina, Brazil, Paraguay, and Uruguay, is one of the largest aquifer systems in the world and is an important source of fresh water. Named after the Guarani people, it covers 1,200,000 km², with a volume of about 40,000 kmÃ,³, thicknesses between 50m and 800m and a maximum depth of about 1,800m.
Aquifer depletion is a problem in some areas, and very important in northern Africa, such as the Great Manmade River project in Libya. However, new methods of groundwater management such as artificial replenishment and surface water injection during the seasonal wet period have extended the life of many freshwater, especially in the United States.
Ogallala's aquifer of the central United States is one of the largest aquifers in the world, but in those places it is rapidly depleted by the growth of urban usage, and the continued use of agriculture. This enormous aquifer, which underlies parts of eight states, contains mainly fossilized water since the last glacial epoch. Annual replenishment, in the drier part of the aquifer, is estimated to account for only about 10 percent of annual withdrawals. According to a 2013 report by hydrological research Leonard F. Konikow at the US Geological Survey (USGS), depletion between 2001-2008, inclusive, is about 32 percent of cumulative depletion during the entire 20th century (Konikow 2013: 22) "In the United States , the largest water user of aquifers including agricultural irrigation and oil and coal extraction. " The total cumulative depletion of cumulative groundwater in the United States accelerated in the late 1940s and continued at an almost stable level through the end of the century. In addition to the widely recognized environmental consequences, groundwater depletion is also adversely affecting the long-term sustainability of groundwater supplies to help meet the nation's water needs. "
An example of a significant and sustained carbonate aquifer is Edwards Aquifer in central Texas. This carboniferic aquifer has historically provided high quality water to nearly 2 million people, and even today, is full of the incredible recharge of a number of streams, rivers and lakes. The main risk for this resource is human development over the catchment area.
The sand body falters at the base of the McMurray Formation in the Athabasca Oil Sands region in northeastern Alberta, Canada, commonly referred to as the Basal Air Aquifer (BWS). Saturated with water, they are limited under the saturated asphalt saturated sand that is exploited to recover the asphalt for synthetic crude production. Where they pause and recharge occurs from their underlying Devonian formation is saline, and where they are shallow and recharged by their non-saline meteoric water. BWS usually causes problems for asphalt recovery, whether by open pit or by in situ methods like steam-assisted gravity drainage (SAGD), and in some areas they target for waste- water injection.
See also
- Aquifer storage and recovery
- The aquifer property
- Aquifer artesis
- Cistern
- Groundwater model
- Ground water pollution
- Hydraulic tomography
- Over-exploit
- Seasonal thermal energy storage - aquifers can be used to store heat or cold between the opposite seasons and for ecological/cooling greenhouse, building, and district heating
- Aquifer aquifer
References
External links
- Falling Water Tables
- IGRAC International Water Resource Assessment Center
- the SahysMod aquifer model
Source of the article : Wikipedia
0 Comments