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Digging a vertical hole in the land to obtain groundwater from the earth is called a well. Wells are also constructed for artificial recharging of water, under ground investigations and inspection, disposal of industrial waste and disposal of flowing refuse. Wells are considered as the simplest traditional method of groundwater exploitation for different uses.
During the present times, main use of wells is to get water for irrigation. According to hydrogeology experts, the well is the name of such water yielding structure through which maximum quantity of groundwater can be extracted on minimum cost according to the capacity of the aquifer. While constructing a well, depth of groundwater level, geological conditions, object of construction of well and economic factors etc. are kept in mind.
After the green revolution, hybrid seeds yielding higher production in agriculture are being used which need comparatively more water. Hence, during present times, a tendency for construction of wells and thereby exploiting water has increased, resulting in converting dark zones in many areas due to overexploitation of groundwater. It is necessary to control it for bringing the situation back to normal.
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While constructing a well, the distance between pumping wells is significant because aquifers inside the earth are located at a definite distance and of definite size. The effective area of a well is dependent on duration and rate of groundwater exploitation, permeability multiplier of aquifer, saturated thickness etc.
In case of difference in any of these factors, the effective area of a well changes. Even on economic basis, it is thought necessary to keep distance between wells. There should be also distance between irrigated areas because some areas may be repeated in the effective area of a well which may make the expenditure on well as unproductive.
For construction of a well, the following geographical conditions are essential:
1. Ground level should not be stony and hard. In stony and hard rocks, digging of a well is not only a difficult task but it is more expensive also.
2. Availability of groundwater reserves in sufficient quantity is necessary. It is useless to excavate a well without sufficient availability of groundwater.
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3. Along with saturated aquifers, there should also be percolation of surface water.
4. There should also be recharge in proportion to exploitation of groundwater.
5. Work of construction of well is also affected by economic factors.
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6. Groundwater should not be situated at great depth.
Types of Wells:
Different type of wells are constructed in different areas on the basis of structure of the ground level, quantity of groundwater and its depth, demand of water for irrigation and economic factors. The quantum of groundwater mainly depends on qualities of aquifer supplying water to the well. Hence, construction of wells should be according to qualities of aquifer. Mainly, depth and diameter are kept in mind while constructing a well.
Depth of well is decided on the basis of distance of aquifer from ground level, size of aquifer, quality of water, and groundwater level. A well can be constructed to the extent of availability of depth of water in aquifer. Similarly, diameter of the well is kept on the basis of rate of exploitation of water and duration. This radius is not affected by natural reasons but it is decided on the basis of artificial technique. Depth of well and its radius is also affected by economic reasons apart from the above factors.
Three types of wells have been constructed by the man. They are:
(1) Kachha Well:
Such wells are constructed in the ground level having hard structure. Their depth is comparatively lesser. Internal wall around all sides of the well is made of clay. Its construction is not possible in case groundwater level is deeper.
(2) Pakka Well:
Their construction is possible up to the depth of the water. Their internal walls are pakka. Their construction is possible due to deeper groundwater. They have greater capacity and their construction is possible even in weaker structure ground level.
(3) Tube well:
The construction by which digging of hole in the earth and bringing water to the ground level through pumps is done, is called a tube well. Construction of tube wells is possible in areas where groundwater is found at a depth of more than 15 metres. They are constructed at places where canal water cannot reach.
The following geological conditions are necessary for construction of tube wells:
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(i) There should be sufficient groundwater below the surface of earth.
(ii) There should be intense demand for irrigation in the area.
(iii) Cheap electricity should be available in sufficient quantity for running the pump set.
(iv) Soil should be productive so as to bear the expenditure of pump set.
(v) Water level should not be at a greater depth than the water surface.
(vi) Need for irrigation exists round the year.
Tube wells are developed when the above conditions are favourible. They are also called open wells. After the tube well revolution, overexploitation of groundwater has resulted. Open wells are deep and their depth is 6-8 metres, more than the depth of groundwater level. Their internal walls are pakka. While constructing a tube well, its size, depth and formation is kept in mind.
Their construction is made by excavating equipment’s in four ways:
1. Digging by percussion
2. Core drilling
3. Through cyclical system
4. By blasting of rocks
Thus, tube wells are constructed according to ground level forms and suitable methods.