Classification of Wells

i. Dug Well

These are shallow wells which are usually constructed in soft ground and soils having sand and gravel. Usual dimensions are up to 4 meter in diameter and up to 20 meter depth. The walls of these wells may be constructed with preset RC blocks, bricks or stone masonry. Cost of these wells is low. Hence they are popular in rural areas and small towns. The yield of these wells is low. The yield can be increased by providing a borehole in the center of the well.

ii. Driven Well

This is also a shallow well. A casing pipe with a sharp point at the bottom is driven into a water bearing stratum. The lower portion of the casing is perforated. The perforated portion of the pipe is covered with a fine mesh to retain sand particles inside the well. The discharge of these wells is very small.

iii. Tube Well

Factories and industrial units need lot of water. Tube wells are popular in such situation because of their higher yield. These wells are constructed using blind pipes and strainer pipes to tap water from many water bearing aquifers. The depth of tube well will be in the range of 50 meter to 500 meter. Depending on geological formation of location, the maximum yield from a tube well may be about 20 liters per second.

Depending on the type of construction, the tube wells are classified as follows:

Strainer Type Tube Well: This type of tube well taps water from all water bearing formations in the well. Strainers are installed in all water bearing formations in the well to allow entry of sand free water. The strainer is nothing but fine wire mesh wrapped around a slotted pipe and soldered or welded to it. Sometimes gravel is packed around the outside of strainer pipe, if the formation contains fine sand or silt.

Slotted Type Tube Well: If the water bearing strata are very deep, then slotted type tube wells are constructed. It consists of slotted wrought iron pipe passing through the main water bearing formation. This pipe is surrounded by gravel packing.

Cavity Type Tube Well: It essentially consists of a blind pipe in its entire length.The bottom is extended up to the aquifer where sufficient water is available. The well is developed by pumping at a faster rate after construction. Loose formation material surrounding the bottom will flow with water and a cavity is formed. The size of the cavity influences the yield of a well.

Perforated Type Tube Well: This type of tube well is constructed by installing perforated pipes. Perforations are made by drilling the pipe. Then the perforated portion is covered with coir or jute rope. The purpose of the rope is to act as a strainer. These are recommended only when water is very near to the ground surface or for temporary water supply.

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