classification of wells

Classification of wells

CLASSIFICATION OF WELLS

The wells may be classified under two heads.

1. Open wells or dug well.

2. Tube wells.

1. Open Wells or Dug Wells.

  • The ancient wells were all open wells.
  • They are constructed by digging large diameter holes in the earth.
  • Although there have been some improvement in methods of digging the wells, in some areas old conventional methods are still prevalent.
  • These wells are initially used to get water for drinking purposes, but later on their use for irrigation purpose was also appreciated.
  • Open wells are generally open masonry wells having diameters varying from 2 m to as much as 7 m.
  • Their depth seldom exceeds 20 m. Their discharge is about 18 m3/hr or about 0.005 cumecs depending upon the depth of water table and nature of soil comprising the aquifer.
  • The walls of the open well may be built of precast concrete, blocks, brick, or stone masonry.
  • The wall is known as staining wall or lining wall of the well.
  • The thickness of lining or staining wall varies between 38 cm and 75 cm depending upon the depth of the well.
  • The yield of an open well is limited because such wells can be dug only to a limited depth.
  • The ground water storage is also limited in the top most aquifer.
  • Moreover open wells cannot be worked at velocity of percolation more than the critical velocity.
  • The velocity more than the critical, causes dislocation of soil grains and consequently develops hollows behind the well lining.
  • Hence, limited velocity of percolation, limited depth of well and limited ground water storage in the top most aquifers, put limit on the yield of the open well.

Open Wells

  • However yield of the open well can be increase, if open well is constructed in top aquifer but in addition 8 to 10 cm diameter hole is bored to puncture the lower layers of water bearing strata.
  • Open wells may further be classifie into two types.

1. Shallow wells and

2. Deep wells.

1. Shallow Well.

  • It is such an open well which gets its supplies from upper most aquifer.
  • If such wells penetrate for small depth under water table, they may even go dry in summer.
  • This is because water from the ground reservoir will soon be drawn out and as soon as water table goes below the bottom of the well it will go dry.
  • Hence in order to get water from such wells for more time or for the year round they should be carried deep into the ground water.
  • Quality of water obtained from shallow wells may not be good for drinking but it is quite good for irrigation purposes.
  • In fact shallow wells can hardly provide substantial irrigation as availability of water is very limited.

 

2. Deep Well.

  • The deep wells get their supplies from water bearing straws lying below an impervious stratum.
  • The theory of deep wells is based on the percolation of water into the under lying aquifers from out-crops.
  • The out-crop is the exposed area of the pervious layer or aquifer, lying below the impervious layer.
  • It is this area from where rain water enters the pervious layers lying below the impervious layer.
  • After getting entry into the layer from out-crop water starts seeping along the slope of the aquifer and reaches the well site.
  • During travel from out crop to well site, water gets thoroughly purified.
  • But during this process certain salts may get dissolved in water and make it hard.
  • Deep wells may get supplies from more than one confined aquifer.
  • Deep wells are not necessarily deeper than shallow wells. It is not the depth of the well but the criteria of getting their supplies.
  • Shallow wells get their water from top most layer but deep wells get their supplies from confined aquifers lying below the impervious layers.
  • A ‘shallow well’ might have more depth than a ‘deep well’.

Mota layer well

  • The impervious layer on which deep wells generally rest and draw their supplies from pervious formations lying below the impervious layer, through a hole is known as Mota layer.
  • The term Mota layer is also sometimes known as ‘Matbarwa’ or ‘Magasan’ layer.
  • This layer refers to a formation of clay, cemented sand, Kankar or other hard materials which are often found lying a few metres below the water table in the sub soil.
  • These names are not used for hard material layers lying above the water table.
  • The main advantage of ‘mota’ layer is that it gives structural support to the open well resting on its surface.
  • It is useful for unlined and partly lined wells and is indispensible for a heavy masonry well which would not remain stable without Mota layer support under steady use.
  • The Mota layer is found throughout the Indo-Gangetic plain.
  • The Mota layer may be present as continuous layer or may be in form of local formation.
  • It has different thicknesses at different places.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Shopping Cart
  • Your basket is empty.
%d bloggers like this: