The total replenishable ground water reserves is highest in
Answers
A part of the rain water percolates in the rocks and soils and is available to us as ground water. The assessment of water resources in India dates back to 1949. Dr. A.N. Khosla (1949) estimated the total average annual run-off of all river systems in India as 167.4 m. ha m (million hectare metre) based on empirical formula which included both surface and ground waters.
Water Resources
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Since then, several attempts have been made to assess the ground water resources in the country. The National Commission on Agriculture (1976), assessed the total ground water of the country as 67 m. ha m, excluding soil mixture. The usable ground water resource was assessed as 35 m. ha m of which 26 m. ha m was considered as available for irrigation.
The first attempt to estimate the ground water resources on scientific basis was made in 1979 when a High Level Committee, known as Ground Water over Exploitation Committee was constituted by Agriculture Refinance and Development Corporation (ARDC). Based on the norms for ground water resources computations recommended by this committee, the State Governments and the Central Ground Water Board computed the gross ground water recharge as 46.79 m. ha m and the net recharge (70% of the gross) as 32.49 m. ha m.
The norms recommended by the Ground Water Estimation Committee (1984) are currently utilized by the Central Ground Water Board and the State Ground Water Departments to compute the ground water Resources.
Based on the recommendations of this committee, the annual replenishable ground water resources in the country work out to be 45.33 m. ha m. Keeping a provision of 15% (6.99 m. ha m) for drinking, industrial and other uses, the utilisable ground water resource for irrigation was computed 38.34 m. ha m per year.
The methodologies adopted for computing ground water resource are generally based on the hydrological techniques.
The main items of supply and disposal of ground water are listed below:
1. Items of supply to ground water reservoir:
(i) Precipitation infiltration to the water table.
(ii) Natural recharge from streams, lakes and ponds.
(iii) Ground water inflow into the area under consideration.
(iv) Recharge from irrigation, reservoirs and other schemes especially designed for artificial recharge.
2. Items of disposal from ground water reservoir:
(i) Evaporation from capillary fringe in areas of shallow water table, and transpiration by vegetation.
(ii) Natural discharge by seepage and spring flow to streams, lakes and ponds.
(iii) Ground water outflow.
(iv) Artificial discharge by pumping or flowing wells or drains.
As per estimates made in late 1980s and early 1990s total replenishable ground water resources have been estimated at 45.22 million hectare metres per year. Of these 38.28 million hectare metres is utilisable for irrigation. The stage of ground water development is about 28% of the utilisable ground water resources.