Water Resources:
Taking the total geographical area of the country at about 328 million hectares and the average annual rainfall at about 112-cm, the total annual precipitation in the country is estimated at about 3,700,000 million cubic metres. The south-westerly monsoon contributes over 80 per cent to the total precipitation in the country. The Central Water and Power Commission, New Delhi, has estimated that of the total annual precipitation amounting to about 800,00 million cubic metres seeps into the ground, about 1,700,000 million cubic metres flows into the rivers and the remaining amount of about 1,200,000 million cubic metres evaporates back into the atmosphere.
Water Resource Categories
The water flowing on the surface and that seeping into the ground, thus, forms the two major sources of water for irrigating crops : the surface-water resources and ground water resources. Each of these categories is a part of the earth's water circulatory system, called the hydrologic cycle, and is ultimately derived from precipitation, which is rainfall plus snow. They are interdependent and frequently the loss of one is the gain of the other.
Surface Water Resources:
A large number of rivers of various potentials and discharges are spread all over the country. The rivers in the north, which originate from the Himalayas, are snow-fed and, thus, have less seasonal fluctuations in their flow than the rivers in other parts of the country. The flow in the rivers of the central and southern parts of the country depends entirely upon the monsoon.
The surface flowing water needs to be trapped in ponds, tanks, lakes, artificial reservoirs when it is available in abundance so that it can be fruitfully used for irrigation during the rainless period to meet the water needs of crops. Of the annual surface flow of 1,700,000 million cubic meters, only about 666,000 million cubic metres can be utilized for the purpose of irrigation owing to the physiographical limitations.
The surface water resources constitutes the total runoff in the stream channels including the snow melt, surface runoff, the subsurface runoff, the ground water runoff and the channel precipitation, e.i. the precipitation falling directly on the water surface of streams, lakes etc.
Canal Irrigation:
Canals draw their water from rivers or from artificial storage. River canals are of three classes :
- Inundation canal
- Perennial canal and
- Storage canal
Ground water resources:
Substantial supplies are also available from ground water sources. Of the 800,000 million cubic metres of rain-water that seeps into theground annually, about 430,000 million cubic metrers of it is absorbed by the surface layers of the earth’s crust and thus can be utilised directly by the vegetation in the process of evapo-transpiration and growth . The remaining 370,000 million cubic metres of rain-water percolates deep into the porous strata of the earth’s crust, representing the gross annual enrichment of the underground water. This ground-water is tapped by digging or drilling shallow or deep wells and is lifted by using mechanical devices for irrigating the crops.
The portion of the precipitation which, after infiltration, reaches the ground water
table, together with the contribution made to ground water table from a neighboring basin, influent rivers, natural lakes, ponds, artificial storage reservoirs, canals, irrigation, and constitutes ground water resources.
Where there is increasing cropping intensity, uncertainty / inadequacy of cheap sources of water, undulated topography and the canal does not feed the area because of their high elevation, well irrigation is one of the solution.
Open Wells
Generally used for multipurpose as domestic use ,irrigation purpose. Run by electrically operated or diesel operated pumpset
Tube Wells/ Filter points well: Shallow tube wells meant for irrigation are privately owned and tap shallow aquifers. These are used to irrigate only a few hectares and have a life period of 5 to 15 years while deep tube-wells generally tap deep aquifers and give a discharge of more than 1,25,000 litres per hour and irrigate a gross area of 80 to 100 ha, the net irrigated area being 20 percent less. These are run for 2,000 to 3,000 hours per annum and have a useful life of 20 to25 years. In shallow aquifers with porous soil strata low cost bamboo tube-wells are constructed. These tube wells are run mostly by electrically operated or diesel operated pumpsets.
Tank Irrigation:
These provide irrigation to a gross area of about 4.5 M ha. Tanks of multipurpose use (pisciculture, duckery, washing, irrigation, flood control, fire control ,agroforestryl,etc.) are of great importance particularly to maintain water supplyu to command area and to recharge groundwater table. The renovation and repair of these tanks are made from the sale of fish, tree on the mounds,etc.
Ag.
Technologies
(Water Mgmt.)
