India has vast ground water resources. The average rainfall over the country is about 110 cm as a whole and this rainfall over India's area of 328 million hectares gives a total precipitation of 3700 billion cubic metres. Only 22 per cent of this total rainfall percolates under the ground. Of this total amount about 430 billion cubic metre reaches upto the upper surface of the soil. Remaining 384 billion cubic metre reaches the pervious strata which could be obtained by dugging the well. But only 70 percent of this amount can be exploited economically.
The underground water resources are affected by the climatic conditions, relief (topography), geological structure and hydrological conditions of the area. Prof. R.L. Singh (1971) has identified 8 ground water provinces within the country
1. Pre-Cambrian Crystalline Province-this is a deficient ground water province covering about one-half of the country's area. It includes Tamil Nadu, Andhra Pradesh, and Karnataka, Maharashtra, Dandakaranya, Bundelkhand and Aravallis.
2. Pre-Cambrian Sedimentary Province-this area is also not suitable for ground water development. Here rocks belonging to the Cuddapah and Vindhyan Systems contain less amount of ground water.
3. Gond wana Sedimentary Province-Here the Gondwana sedimentary rocks of the Barakar and Godavari river basins contain good-aquifers for water.
4. Deccan Trap Province-this region is also deficient in ground water due to a 1, 2(X) metre thick covering of basalt over the surface which obstructs percolation. The only aquifers preserved arc in the fractures where secondary porosity develops in the weathered moorums, at times in the intertrappean beds sandwitched between two impermeable strata as also in the vesicles and the amygdales.
5. Cenozoic Sedimentary Province-this includes coastal areas of Andhra Pradesh, Tamil Nadu, Kerala and Gujarat where Tertiary sandstones and slates provide good aquifers.
6. Cenozoic Fault Basin-the rift zone of the Narmada, Purna and Tapi rivers provides rich resource of ground water in their 80-160 m thick alluvial cover of sand, silt and clay.
7. Ganga-Brahmaputra Alluvial Province-this forms the richest ground water province of the country. Here Bhabar, Tarai, axial belts and alluviums encourage percolation and contain good storage of ground water
8. Himalayan Province-this complex structural and geographic unit is not very significant with respect to ground water resources. It provides a number of natural springs but the dug wells arc rare feature to be seen. According to the Central Ground Water Commission about 44 per cent of the underground water resources are concentrated in the Ganga- Brahmaputra Basin. Here 100-150 cumic meters per hour water is available at the depth of 600 meters. This is also corroborated by NATMO.
Table 4 III presents a summary of the availability of ground water in different parts of the country. According to the recent findings there is possibility of per hour ground water yield of 80 cubic meters in Tamil Nadu, 50cubic meters in Karnataka, 30 cubic meters in Madhya Pradesh and 28 cubic meters in Maharashtra.
Before the commencement of the planning era (i.e. in 1948) 97 lakh hectares of water was available for irrigation. But by the year 1973 the figure rose to 184 lakh hectares. Despite the phenomenal development of ground water resources two-third of them are still undeveloped. Figure 4.9 exhibits the region-wise utilisation of ground water resources in India. In Punjab, Haryana, Delhi, Chandigarh ground water resources have been overexploited. For proper exploitation of ground water there is a need for power driven pump sets whose availability has been ensured through Rural Electrification Corporation (REC) established in 1969.
According to REC at present there are 72 lakh power driven pump sets (31 lakh by REC) under operation in different parts of the country which provide irrigation to about 14.4 million hectares of land through ground water. According to another estimate the total ground water resource potential is about 44 million ha. Whose 27 per cent is currently being exploited creating an irrigation potential of about 35 million ha.