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About 300 lakh hectare metre Groundwater is available in India at present. After complete development of surface water resources, it is expected to become 350 lakh hectare metre. Till the end of the Fourth Five-Year Plan, hardly 160 lakh hectare metre Groundwater could be utilized.
At present at least 240 lakh hectare metre underground water can be used. Unfortunately, every year quantity of underground water is reducing. Although about 270 lakh hectare metre water is added to underground water every year through infiltration of rain water and seepage from canals, but so much excess water is being used in agriculture and industry that the water level is going lower and lower day by day.
According to Geological Survey of India, groundwater in India can be divided into three parts:
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1. Rocky plateau area
2. Alluvial area
3. Integrated sedimentary area
About seventy per cent area of the country is rocky plateau area. Here water is available in very limited quantity and only from open wells. In the alluvial area of Indus and Ganges, there is a vast reservoir of water which has its own place in the world. In the south, there is sufficient water m the alluvial area of coastal regions. In the western depth water is estimated at 100-150 metres
R.L. Singh, in his book India:
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A Regional Geography has divided groundwater areas of India into eight regions as under:
1. Precambrtan Crystalline Rocky Region:
Almost half of the area of the country is included in this region, which extends to Tamil Nadu, Karnataka, Andhra Pradesh, Drandakaranya, Bundelkhand ,Aravali etc.
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2. Precambrean Sedimentary Rocky Region:
This area extends to Cuddappa and Vindhyan Basin.
3. Gondwana Sedimentary Rocky Region:
Sufficient water is found in this region that is in the Barakar and Godavari basin area, which have sand rocks.
4. Deccan Trap Region:
In this region there is a 1200 metre thick impermeable basalt strip where there is shortage of groundwater.
5. Cenozoic Sedimentary Rocky Region:
This is the tertiary carpet having sufficient groundwater, which is located in the coastal parts of Tamil Nadu, Andhra Pradesh, Kerala and Gujarat.
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6. Cenozoic Fault Basin Region:
Situated in the fault basins of Narmada, Tapti and Purna rivers, sufficient groundwater from Kamp Jamav is available (80 to 160 metre deep) here.
7 Ganges Brahmaputra Alluvial Region:
In this region, there is enormous water at the upper level.
8. Himalayan Region:
This is not important from the point of view of groundwater, the main reason being its compact composition.
Out of the total water available in India, only 1,104 lakh hectare metre or 46 per cent water is used, which includes use of water for agriculture, domestic settlements including cattle, and for industries.
The above figures reveal that quantity of water has increased from 380 lakh hectare metres in 1974 to 540 lakh hectare metres in 1985. The required demand for water in 2000 as per figures was 750 lakh hectare metres but the demands for food, fodder, fuel and land based raw material for industries for a population of 10,000 lakhs up to the year 2005 has to be taken into account. In such a context, reassessment of such items has been done. Due to increasing needs of water, 280 hectare metres water out of the total water resources of India is being used for industries, electricity, urbanization etc.
Thus, only 913.2 lakh hectare metre water will be available for agriculture. As per National Water Policy, water available for irrigation would be able to irrigate at least 25 per cent of sown area. Total sown area is 1,500 lakh hectares out of which only 11,250 lakh hectares should be irrigated.
As compared to surface water, groundwater is less expensive and more qualitative. It has been estimated that underground water extends to approximately 452 sq. kms area in India. At present, our country is utilizing about 45.22 million hectare underground water, of which 38.38 million hectare is used for irrigation and 6.94 million hectare for industries and domestic consumption.
Underground water is a moving and renewable resource and its estimate is mainly based on annual availability of water. Thus, availability of groundwater depends on geological and climatic conditions. Annual demand of usable groundwater for the country has been estimated to be 4.5 crore hectare metres. Out of this estimated demand 3.85 crore hectare ground-water is available for irrigation, whereas 68.3 lakh hectare metres is for drinking water, industries and other essential uses.
In eastern Uttar Pradesh, Bihar, West Bengal and Orissa there is thick layer of marshy soil spread over the ground, hence they are most suitable for underground development because of lesser depth. The level of groundwater development is 6 per cent in Orissa, 19 per cent in Bihar, 24 per cent in West Bengal and 34 per cent in Western Uttar Pradesh. Since, the depth of groundwater in these states varies from 5 to 10 metres, hence use of groundwater can be comparatively easier here.