Water table

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.[1]

The water table is the surface where the water pressure head is equal to the atmospheric pressure (where gauge pressure = 0). It may be visualized as the "surface" of the subsurface materials that are saturated with groundwater in a given vicinity.[2]

The groundwater may be from precipitation or from groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths, water fills in more of the pore spaces in the soils, until a zone of saturation is reached. Below the water table, in the phreatic zone (zone of saturation), layers of permeable rock that yield groundwater are called aquifers. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define.

The water table should not be confused with the water level in a deeper well. If a deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in this aquifer may rise to a level that is greater or less than the elevation of the actual water table. The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface, not the water table.[2]

Water table
Cross section showing the water table varying with surface topography as well as a perched water table

Form

The water table may vary due to seasonal changes such as precipitation and evapotranspiration. In undeveloped regions with permeable soils that receive sufficient amounts of precipitation, the water table typically slopes toward rivers that act to drain the groundwater away and release the pressure in the aquifer. Springs, rivers, lakes and oases occur when the water table reaches the surface. Groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies.[3]

Surface topography

Within an aquifer, the water table is rarely horizontal, but reflects the surface relief due to the capillary effect[4] (capillary fringe) in soils, sediments and other porous media. In the aquifer, groundwater flows from points of higher pressure to points of lower pressure, and the direction of groundwater flow typically has both a horizontal and a vertical component. The slope of the water table is known as the hydraulic gradient, which depends on the rate at which water is added to and removed from the aquifer and the permeability of the material. The water table does not always mimic the topography due to variations in the underlying geological structure (e.g., folded, faulted, fractured bedrock).

Perched water tables

A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. This occurs when there is an impermeable layer of rock or sediment (aquiclude) or relatively impermeable layer (aquitard) above the main water table/aquifer but below the land surface. If a perched aquifer's flow intersects the surface, at a valley wall, for example, the water is discharged as a spring.

Fluctuations

Water table-season fluctuation
Seasonal fluctuations in the water table-during the dry season, river beds may dry up.

Tidal fluctuations

On low-lying oceanic islands with porous soil, freshwater tends to collect in lenticular pools on top of the denser seawater intruding from the sides of the islands. Such an island's freshwater lens, and thus the water table, rises and falls with the tides.

Seasonal fluctuations

In some regions, for example, Great Britain or California, winter precipitation is often higher than summer precipitation and so the groundwater storage is not fully recharged in summer. Consequently, the water table is lower during the summer. This disparity between the level of the winter and summer water table is known as the "zone of intermittent saturation", wherein the water table will fluctuate in response to climatic conditions.

Long-term fluctuations

Fossil water is groundwater that has remained in an aquifer for several millennia and occurs mainly in deserts. It is non-renewable by present-day rainfall due to its depth below the surface, and any extraction causes a permanent change in the water table in such regions.

Effects on sea level

Aquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise.[5]

Effects on crop yield

Rudd PartReg
Yield of sugarcane versus depth of the water table, Australia. The critical depth is 0.6 m.[6][7]

Most crops need a water table at a minimum depth because at shallower depths the crop suffers a yield decline.[8] For some important food and fiber crops a classification was made:[9]

Crop and location DWT tolerance Classification Explanation
Wheat, Nile Delta, Egypt 45 Very tolerant Resists shallow water tables
Sugar cane, Australia 60 Tolerant The water table should be deeper than 60 cm
Banana, Surinam 70 Slightly sensitive Yield declines at water tables < than 70 cm deep
Cotton, Nile Delta 90 Sensitive Cotton needs dry feet, water table should be deep
(Where DWT = depth to water table in centimetres)

See also

References

  1. ^ "What is the Water Table?". imnh.isu.edu. Retrieved 2016-11-25.
  2. ^ a b Freeze, R. Allan; Cherry, John A. (1979). Groundwater. Englewood Cliffs, NJ: Prentice-Hall. OCLC 252025686.
  3. ^ Winter, Thomas C; Harvey, Judson W (1998). "Ground Water and Surface Water A Single Resource - U.S. Geological Survey Circular 1139" (PDF). Retrieved 25 August 2018.
  4. ^ "Water table". www.tititudorancea.com. Retrieved 2018-08-24.
  5. ^ "Rising sea levels attributed to global groundwater extraction". University of Utrecht. Retrieved February 8, 2011.
  6. ^ Rudd, A.V. and C.W Chardon 1977. The effects of drainage on cane yields as measured by water table height in the Machnade Mill area. In: Proceedings of the 44th Conference of the Queensland Society of Sugar Cane Technology, Australia.
  7. ^ Software for partial regression with horizontal segment
  8. ^ K.J.Lenselink et al. Crop tolerance to shallow water tables. Online: [1]
  9. ^ Nijland, H.J. and S. El Guindy 1984. Crop yields, soil salinity and water table depth in the Nile Delta. In: ILRI Annual Report 1983, Wageningen, The Netherlands, pp. 19–29. Online: [2]
Acrotelm

The acrotelm is one of two distinct layers in undisturbed peat bogs. It overlies the catotelm. The boundary between the two layers is defined by the transition from peat containing living plants (acrotelm) to peat containing dead plant material (catotelm). This typically coincides with the lowest level of the water table. Fluctuations in water table in a peat bog occur within the acrotelm, and hence conditions may vary from aerobic to anaerobic with time.

Aquifer

An aquifer is an underground layer of water-bearing permeable rock, rock fractures or unconsolidated materials (gravel, sand, or silt). Groundwater can be extracted using a water well. 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 (or aquifuge), which is a solid, impermeable area underlying or overlying an aquifer. If the impermeable area overlies the aquifer, pressure could cause it to become a confined aquifer.

Artesian aquifer

See Great Artesian Basin for the water source in Australia.

An aquifer is a geologic layer of porous and permeable material such as sand and gravel, limestone, or sandstone, through which water flows and is stored. An artesian aquifer is a confined aquifer containing groundwater under positive pressure. An artesian aquifer is trapped water, surrounded by layers of impermeable rock or clay which apply positive pressure to the water contained within the aquifer. If a well were to be sunk into an artesian aquifer, water in the well-pipe would rise to a height corresponding to the point where hydrostatic equilibrium is reached.

A well drilled into such an aquifer is called an artesian well. If water reaches the ground surface under the natural pressure of the aquifer, the well is termed a flowing artesian well.Fossil water aquifers can also be artesian if they are under sufficient pressure from the surrounding rocks, similarly to how many newly tapped oil wells are pressurized.

From the previous statement, it can be inferred that not all aquifers are artesian (i.e. water table aquifers occur where the groundwater level at the top of the aquifer is at equilibrium with atmospheric pressure). The recharging of aquifers happens when the water table at its recharge zone is at a higher elevation than the head of the well.

Artesian wells were named after the former province of Artois in France, where many artesian wells were drilled by Carthusian monks from 1126.

Aylesbury Vale

The Aylesbury Vale (or Vale of Aylesbury) is a large area of gently rolling agricultural landscape located in the northern half of Buckinghamshire, England. Its boundary is marked by the Borough of Milton Keynes and South Northamptonshire to the north, Central Bedfordshire and the Borough of Dacorum (Hertfordshire) to the east, the Chiltern Hills and Wycombe to south, and South Oxfordshire to the west.

The vale is named after Aylesbury, the county town of Buckinghamshire. The two other towns which lie within the vale are Winslow and Buckingham.

The bed of the vale is largely made up of clay that was formed at the end of the ice age. Also at this time the vast underground reserves of water that make the water table in the Vale of Aylesbury higher than average, were created.

In the 2011 UK census the population of Aylesbury Vale was 174,900.

In the 2001 UK census the population of Aylesbury Vale was 165,748, representing an increase since 1991 of 18,600 people. About half of those live in the county town Aylesbury.

Florida swamps

Florida swamps include a variety of wetland habitats. Because of its high water table, substantial rainfall, and often flat geography, the U.S. state of Florida has a proliferation of swamp areas, some of them unique to the state.

Swamp types in Florida include:

Cypress dome - most common swamp habitat in Florida

Strand swamp

Floodplain swamp

Titi swamp

Tupelo gum swamp

Mangrove swamp

Gadilam River

The Gadilam River (sometimes pronounced Kedilam) flows through the Cuddalore and Villupuram districts of Tamil Nadu.It has a small water flow, drainage area and sand deposit.

It is generally flooded during the monsoon season and raises the water table and feed tanks on its basin.

Few famous temples like Thiruvathigai Veerataneshwar temple and Thiruvanthipuram Thevanathan perumal temple are located in its banks. It is also mentioned in the Medieval Bhakti literatures like Thevaram.

The Gadilam River flows through the town of Cuddalore and separates the Old Town from Thirupadiripuliyr.

Groundwater

Groundwater is the water present beneath Earth's surface in soil pore spaces and in the fractures of rock formations. 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 and eventually flows to the surface naturally; natural discharge often occurs 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.

Typically, groundwater is thought of as water flowing through shallow aquifers, but, in the technical sense, it can also contain soil moisture, permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of Earth's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of Jupiter's moon Europa.Groundwater is often cheaper, more convenient and less vulnerable to pollution than surface water. Therefore, it is commonly used for public water supplies. For example, groundwater provides the largest source of usable water storage in the United States, and California annually withdraws the largest amount of groundwater of all the states. Underground reservoirs contain far more water than the capacity of all surface reservoirs and lakes in the US, including the Great Lakes. Many municipal water supplies are derived solely from groundwater.Polluted groundwater is less visible and more difficult to clean up than pollution in rivers and lakes. Groundwater pollution most often results from improper disposal of wastes on land. Major sources include industrial and household chemicals and garbage landfills, excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems.

Groundwater recharge

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 (through the water cycle) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and or reclaimed water is routed to the subsurface.

Hydraulic conductivity

Hydraulic conductivity, symbolically represented as , is a property of vascular plants, soils and rocks, that describes the ease with which a fluid (usually water) can move through pore spaces or fractures. It depends on the intrinsic permeability of the material, the degree of saturation, and on the density and viscosity of the fluid. Saturated hydraulic conductivity, Ksat, describes water movement through saturated media. By definition, hydraulic conductivity is the ratio of velocity to hydraulic gradient indicating permeability of porous media.

Malachite

Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.

Mount Gambier (volcano)

Mount Gambier (also known as Ereng Balam, meaning eagle hawk) is a maar complex in South Australia associated with the Newer Volcanics Province. It contains four lake-filled maars called Blue Lake, Valley Lake, Leg of Mutton Lake, and Browns Lake. Both Brown and Leg of Mutton lakes are dry in recent years, due to the lowering of the water table.

It is one of Australia's youngest volcanoes, but estimates of the age have ranged from over 28,000 to less than 4,300.

The most recent estimate, based on radiocarbon dating of plant fibers in the main crater (Blue Lake) suggests an eruption a little before 6000 years ago.

It is believed to be dormant rather than extinct.

Mount Gambier is thought to have formed by a mantle plume centre called the East Australia hotspot which may currently lie offshore.The mountain was sighted by Lieutenant James Grant on 3 December 1800 from the survey brig HMS Lady Nelson and named for Lord James Gambier, Admiral of the Fleet.This area is part of the UNESCO-endorsed Kanawinka Geopark.

Of the original four lakes found within the maars, only two remain. The Leg of Mutton Lake (named for the outline of its shoreline) became permanently dry in the 1990s. Browns Lake suffered a similar fate during the late 1980s. Both these lakes were quite shallow; their demise is attributed to the lowering of the water table as a result of many years of land drainage to secure farmland.

The city of Mount Gambier partially surrounds the maar complex.

Pore water pressure

Pore water pressure (sometimes abbreviated to pwp) refers to the pressure of groundwater held within a soil or rock, in gaps between particles (pores). Pore water pressures below the phreatic level of the groundwater are measured with piezometers. The vertical pore water pressure distribution in aquifers can generally be assumed to be close to hydrostatic.

In the unsaturated zone, the pore pressure is determined by capillarity and is also referred to as tension, suction, or matric pressure. Pore water pressures under unsaturated conditions (vadose zone) are measured in with tensiometers. Tensiometers operate by allowing the pore water to come into equilibrium with a reference pressure indicator through a permeable ceramic cup placed in contact with the soil.

Pore water pressure is vital in calculating the stress state in the ground soil mechanics, from Terzaghi's expression for the effective stress of a soil.

Sewerage

Sewerage is the infrastructure that conveys sewage or surface runoff (stormwater, meltwater, rainwater) using sewers. It encompasses components such as receiving drains, manholes, pumping stations, storm overflows, and screening chambers of the combined sewer or sanitary sewer. Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment. It is the system of pipes, chambers, manholes, etc. that conveys the sewage or storm water.

It is also an alternate noun for the word sewage.

In American colloquial English, "sewer system" is applied more frequently to the large infrastructure of sewers that British speakers more often refer to as "sewerage".

Soil salinity control

Soil salinity control relates to controlling the problem of soil salinity and reclaiming salinized agricultural land.

The aim of soil salinity control is to prevent soil degradation by salination and reclaim already salty (saline) soils. Soil reclamation is also called soil improvement, rehabilitation, remediation, recuperation, or amelioration.

The primary man-made cause of salinization is irrigation. River water or groundwater used in irrigation contains salts, which remain behind in the soil after the water has evaporated.

The primary method of controlling soil salinity is to permit 10-20% of the irrigation water to leach the soil,that will be drained and discharged through an appropriate drainage system. The salt concentration of the drainage water is normally 5 to 10 times higher than that of the irrigation water, thus salt export matches salt import and it will not accumulate.

Sump pump

A sump pump is a pump used to remove water that has accumulated in a water-collecting sump basin, commonly found in the basements of homes. The water may enter via the perimeter drains of a basement waterproofing system, funneling into the basin or because of rain or natural ground water, if the basement is below the water table level.

Sump pumps are used where basement flooding happens regularly and to solve dampness where the water table is above the foundation of a home. Sump pumps send water away from a house to any place where it is no longer problematic, such as a municipal storm drain or a dry well.

Pumps may discharge to the sanitary sewer in older installations. Once considered acceptable, this practice may now violate the plumbing code or municipal bylaws, because it can overwhelm the municipal sewage treatment system. Municipalities urge homeowners to disconnect and reroute sump pump discharge away from sanitary sewers. Fines may be imposed for noncompliance. Many homeowners have inherited their sump pump configurations and do not realize that the pump discharges into the sewer.

Usually hardwired into a home's electrical system, sump pumps may have a battery backup. The home's pressurized water supply powers some pumps, eliminating the need for electricity at the expense of using potable water, potentially making them more expensive to operate than electrical pumps and creating an additional water disposal problem. Since a sump basin may overflow if not constantly pumped, a backup system is important for cases when the main power is out for prolonged periods of time, as during a severe storm.

There are generally two types of sump pumps—pedestal and submersible. In the case of the pedestal pump, the motor is mounted above the sump—where it is more easily serviced, but is also more conspicuous. The pump impeller is driven by a long, vertical extension shaft and the impeller is in a scroll housing in the base of the pump. The submersible pump, on the other hand, is entirely mounted inside the sump, and is specially sealed to prevent electrical short circuits. There is debate about which variety of sump pump is better. Pedestal sump pumps usually last longer (25 to 30 years) if they are installed properly and kept free of debris. They are less expensive and easier to remove. Submersible pumps will only last 5 to 15 years. They are more expensive to purchase but can take up debris without clogging.Sump pump systems are also utilized in industrial and commercial applications to control water table-related problems in surface soil. An artesian aquifer or periodic high water table situation can cause the ground to become unstable due to water saturation. As long as the pump functions, the surface soil will remain stable. These sumps are typically ten feet in depth or more; lined with corrugated metal pipe that contains perforations or drain holes throughout. They may include electronic control systems with visual and audible alarms and are usually covered to prevent debris and animals from falling in.

Table

Table may refer to:

Table (furniture), an item of furniture with a flat top and one or more legs

Table (information), a data arrangement with rows and columns

Table (database)

Calligra Tables, a spreadsheet application

Mathematical table

Table (landform)

Table (parliamentary procedure)

Tables (board game)

The Table, a volcanic tuya in British Columbia, Canada

Table, surface of the sound board (music) of a string instrument

Al-Ma'ida, the fifth sura of the Qur'an, usually translated as “The Table”

Water table

Vadose zone

The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin for "shallow"). Hence, the vadose zone extends from the top of the ground surface to the water table.

Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion (funiculary groundwater), and capillary action (capillary groundwater). If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe. Movement of water within the vadose zone is studied within soil physics and hydrology, particularly hydrogeology, and is of importance to agriculture, contaminant transport, and flood control. The Richards equation is often used to mathematically describe the flow of water, which is based partially on Darcy's law. Groundwater recharge, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation.

Water table (architecture)

A water table is a masonry architectural feature that consists of a projecting course that deflects water running down the face of a building away from lower courses or the foundation, though they are often primarily decorative. A water table may be found near the base of a wall or at a transition between materials, such as from stone to brick.

A water table is a projection of lower masonry on the outside of the wall slightly above the ground. Often a damp

course is placed at the level of the water table to prevent upward penetration of ground water.

Windover Archeological Site

The Windover Archeological Site is an Early Archaic (6000 to 5000 BC) archaeological site and National Historic Landmark in Brevard County near Titusville, Florida, USA, on the central east coast of the state. Windover is a muck pond where skeletal remains of 168 individuals were found buried in the peat at the bottom of the pond. The skeletons were well preserved because of the characteristics of peat. In addition, remarkably well-preserved brain tissue has been recovered from many skulls from the site. DNA from the brain tissue has been sequenced. The collection of human skeletal remains and artifacts recovered from Windover Pond represent among the largest finds of each type from the Archaic Period. It is considered one of the most important archeological sites ever excavated.

The Windover dig site is a small pond, about .25 acres (1,000 m2) in area, that has held water continuously since sometime between 9000 and 8000 BC. It is next to the Atlantic coastal ridge about 5 miles (8 km) from Cape Canaveral. As the sea level was considerably lower 7,000 to 8,000 years ago than it is today, the pond originally sat above the water table, and was filled only by rainfall and runoff from the surrounding land. At that time the pond had a relatively thin layer of peat under a thin layer of water. The subsequent rise in sea level raised the local water table, and in more recent times the pond has been fed by groundwater as well as rainfall. In 1984 the pond had a thick layer of peat, with five strata described by the archaeologists who excavated the pond. The peat in the center of the pond was covered by 6 feet (2 m) of water.

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