Water is an important resource. India has plenty of fresh water. Most of the fresh water is received during monsoon months unlike land; availability of water varies from place to place and time to time. Bulk of rain fall, is confined to a brief period of 3-4 months and this large part of the country takes, supply of water for a greater part of the year.
Water Resources: Indian Scenario :
India is a country of vast biological, geographic, and climatic diversity. It has total geographic area of 329 Mha; excluding bodies of water, India’s total land area is estimated at 297 Mha.
India is bordered in the north by the 2,500- kilometer long Himalayan Mountains. Melting snow and glaciers provide a continuous flow for numerous rivers running south from the Himalayas into the vast Indo-genetic Plain, which is dominated by the Ganges River and its tributaries. Heavy rains are typical in the Himalayas during the monsoon months between June and October, causing frequent floods. Southern India consists largely of the Deccan Plateau, which is flanked by the Western Ghats running along the west coast and the smaller Eastern Ghats of the east coast. The Deccan Rivers are rain fed and fluctuate in volume; many of these rivers are not perennial.
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India receives average annual precipitation of 4000 km3, out of which 700 km3 is immediately lost of the atmosphere, 2150 km3 soaks into the ground, and 1150 km3 flows as surface run-off as in figure 1.
India is one of the few countries in the world endowed with abundant land and water resources. Average annual precipitation including snowfall over the country is 4000 billion cubic meters (BCM). In addition, it receives another 200 BCM from rivers flowing in from other countries. Average annual water resources in various river basins are estimated to be 1869 BCM, of which the utilizable volume of water has been estimated to be 1086 BCM including 690 BCM of surface water and 396 BCM of ground water. The rest of the water is lost by evaporation or flows into the sea and goes waste. The utilization of water is expected to be 784 to 843 BCM by the year 2025. Though the present utilization level is only about 50%, the availability of water is highly irregular. It is not available in places of need, at times of need and required quantities.
In the major part of the country, rainfall is the only sources for water which is available mainly during the monsoon season lasting for less than 3 months. Due to tropical climate and it’s geographical, location, the country experiences vast spatial and temporal variation in precipitation. About one- third of the country’s area is drought prone. The south and western parts comprising the states of Rajasthan, Gujarat, Andhra Pradesh, Madhya Pradesh, Maharashtra, Tamil Nadu and Karnataka are the drought prone states. On the other hand, north and north eastern regions including states of Uttar Pradesh, Bihar, West Bengal and Assam (Asom) are subjected to periodic flooding.
Water resources are as follows:
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(1) Surface Water:
In India, surface flow takes place through 14 major rivers systems. Between them they share 83% of the drainage basin, account for 85% of the surface flow and house 80% of the total population of the country. In addition to major rivers there are 44 medium and 55 minor systems. These are fast flowing and monsoon fed. The surface flow is further enlarged by addition of about 450 cubic kms. of fresh water from ground water flow while about 50 cubic kms are added to runoff from irrigated areas. Out of this surface water flow about same amount of water percolates down to the ground water deposits.
(2) Ground Water:
Ground water resources are abundant only in the northern and coastal plains. Underground reservoir of fresh water is called aquifers. Ground water are continuously reached through infiltration, seepage and evatranspiration. Presently about 25% of the ground water is being used by man. Agriculture uses maximum amount of ground water.
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It has been found that excessive use of ground water depletes aquafers, lowers the water table and may lead to salivation, water logging and alkalization of the soils. According to the initial estimates of the Central Ground Water Board an additional quantity of about 10,081 km3 of static ground water can be exploited.
Generally static water is not regular replenished on annual basis; its one time use is only possible as a short time strategy. Further experience indicates that large scale use of static water or its mining is usually associated with surface settlement which may cause heavy damages to properties of land and soils and may, possibly, trigger seismic activities. Therefore, any appreciable use of static ground water on regular basis is not foreseen till the middle of the 21st century.
India receives about 3 trillion M3 of water from rainfall. This is a huge resource and perhaps largest in the world. However, almost 90% of this precipitation falls between mid June and October, out of which India utilizes only 10%.