The Work of Running Water and Underground Water: Water Table, Types of Water Table, Wells, Tube wells and Artesian Wells

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Water Table

  • The water table marks the upper surface of the saturated zone of the ground water, where pores are completely full of water. The zones or horizons of permeable and porous rocks which are fully filled with water are called the zones of saturation.

  • The upper level of this zone, below which the rocks are completely saturated with water is called the underground water level or the water table. The rocks containing underground water are called aquifers.

Image of Image of Water Table

Image of Image of Water Table

Types of Water Table

The level of the ground water table always fluctuates. The level of the water table is controlled by the nature of land surface, variation in the amount of rainfall, and the character of the underlying rocks. Water table is generally higher in areas of high precipitation and in areas bordering rivers and lakes. Water table changes according to seasons. It is higher in rainy season and lower during summers. On the basis of the variability, the water table is of two types:

  • Permanent Water Table: When the water table is stable or static and never falls below a particular level, it is called the permanent water table. It is not affected by seasonal change. Wells dug up to this depth provide water in all seasons. They are perennial wells.

  • Temporary Water Table: The level at which the water table is not stable, keeps changing with season is called temporary water table. It means that during the wet season, the water table will be higher than it is during the dry season. Thus, it is also known as seasonal water table. Wells dug up to this level are not perennial. They dry up during the summer season.

Wells, Tube Wells and Artesian Wells

Wells and tube wells are man-made holes dug into the earth’s surface through which underground water is drawn for drinking purpose and for irrigation. They are either bored mechanically as in the case of tube wells or are dug by man as in the case of wells to reach a permanent water table.

A special type of well in which water rises automatically under its own pressure to the surface, either through a natural or a man-made hole is known as an artesian well. The name artesian has been derived from the province of Artois in France, where the first well of this type was dug. Certain conditions are prerequisite of an artesian well. They are:

  • Arrangement of Rocks: For an artesian well, there should be layer of permeable rock lying between two impermeable rock layers. In such case, water present in the permeable rock does not escape.

  • Structure of Rock Strata: The rock must have a synclinal or tilted structure.

  • Intake Area of the Rock: The permeable rock should be exposed at the ground surface, so that rock can soak rainwater. This intake area should be sufficiently high so that enough hydraulic pressure will be developed to force the water upward in the well.

  • Availability of Water: There should be sufficient amount of precipitation or infiltration of water in the area where the permeable rock is exposed at the surface.

Springs and Geysers

Springs are surface outflow of ground water through an opening in a rock under hydraulic pressure. In such cases the aquifer is either exposed at the surface or it underlies an impermeable rock. The amount of water in the aquifer depends upon the amount of rainfall in that area, landform characteristic and the size of the aquifer.

  • Hot Spring: Sometimes the water that flows out of the spring is hot. Such springs are called hot springs. They generally occur in areas of active or recent vulcanism. In volcanic regions the underground water gets heated up by coming in contact with hot rocks or steam. Hot springs are found in many parts of India, especially in the Himalaya in Jammu and Kashmir and Himachal Pradesh. Manikaran in Kulu Valley, Tatapani near Shimla, Jwalamukhi in Kangra, Sohna in Haryana, Rajgir and Sitakund in Jharkhand and Badrinath in Uttarakhand have hot springs.

  • Geyser: Springs emitting hot water and steam in forms of fountains or jets at regular intervals are known as geysers. In case of a geyser, hot water is ejected violently because of the pressure created by steam. The period between two emissions is sometimes regular. The best example of geysers working at a regular interval is the Old Faithful Geyser in the Yellowstone National Park of U.S.A which is situated in the Rocky Mountain region. Its regularity is so accurate that tourists correct their watches by it. Geysers are found in Iceland, and the northern part of New Zealand.

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