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by Aryadasa Ratnasinghe

Water (H2 O) is the commonest molecular compound on earth. It covers about 70 percent of the earth's surface, and dissolves almost everything to some extent.

However, it is a poor solvent for substances which are found in solution form. Water is essential to life and occurs in all living organisms. In solid form it has less density than liquid, and it is for this reason that ice floats on water.

The basic need for proper utilisation of water is education to know how to use it wisely and carefully to prevent waste. In most towns supplied with pipe-borne water, the people are advised to save water without allowing it to go down the drain. Water is both the most abundant and the most important substance with which man deals with no care. Quantities

The quantities of water required by man for his different uses vary over a wide range. It is said that the quantum of drinking water needed each year by human beings as well as animals, is of the order of 10 tons per ton of living tissue in the body. To grow a ton of sugar cane, under irrigation, requires about 1,000 tons of water, leaving room for soil evaporation and plant transpiration from liquid to vapour. For rice cultivation, the requirement is about 4,000 to 10,000 tons of water per ton of crop, depending on the type of soil and the layout of the field. The position is worse during the dry season due to lack of rainfall, sometimes subsidised by irrigation water.

Most rivers discharge their confluence into the sea, unused by man, and more than half of the water requirement is lost by evaporation during hot weather. Harnessing of rain water for irrigation purposes was known to man from remote antiquity, and for this purpose our kings build tanks and reservoirs of enormous size to store large stocks of water for use when rains fail or during the dry season when water was scanty to feed the growing plants.

Most of the paddy fields in the upland country are rain-fed as irrigation is not possible due to the topography of the land.

Irrigation agriculture was known to the farmers in Sri Lanka from ancient times. Kings, who took to irrigation, built tanks of large size to store bulk water for use during drought season. Among the works of public utility, with which king Pandukabhaya (BC 437-407) stands credited, is the construction of the Abhayavapi tank, which is today known as Basavakkulama in Anuradhapura. It is the earliest constructive work which can be identified with certainty. Hence it was the first of the irrigation systems which formed a very special feature of the ancient civilisation of Sri Lanka.

The irrigation system, intended to store or convey water for the paddy fields, which the Sinhalese had begun in cultivating the staple crop (rice) is evident. The system they adopted at first was to impound water in tanks or reservoirs with low embankments, mostly by dredging the earth to make them deep and to conserve more water.

From these, the water was gradually passed out to the fields, either directly through anicuts or by means of excavated channels for the convenient flow of water to irrigate the fields, at low ground.

Embankments

Later, however, when the people had acquired a better knowledge of the art of raising embankments to hold back greater depths of water, the constructive genius of the farmer asserted itself, and systems of a more comprehensive nature were attempted. Great earthen embankments, often some miles in length, were raised across many suitable valleys, intercepting in this manner, the flow of the streams and storing up water, during the rainy season, in the tanks thus built, immense sheets of water for irrigating large extents of land, lower down in the valleys, that were found suitable for paddy cultivation.

The tanks were well designed to fulfil their purpose. the now Basavakkulama, in addition to supply of water to paddy fields, also supplied water to the city of Anuradhapura for drinking and bathing purposes. The tank was well protected from pollution to prevent water-borne diseases, and the contamination of other harmful matter.

This tank was so well constructed that it remained unbreached for more than 1,500 years (the end of Anuradhapura period).

One of the most promising and efficient ways to increase the productivity or the productive capacity of land is the development of water resources for irrigation. By the sound use of irrigation water, in combination with improved seeds, fertilizers, tillage practices, soil conservation measures, crop rotation etc. output can be increased considerably and levels of consumption and nutrition improved, as a result of more diversified production of rice.

Irrigation is more than a technique. It is the way to find water to distant fields, particularly settlement of the newly irrigated zones. Appropriate action, where necessary, should be applied to prevent water logging, salinity and the leaching of nutrients. Over-irrigation should be avoided and the volume of water distributed should be determined on the basis of an accurate knowledge of crop requirement.

Irrigation agriculture, where rainfall is scanty, is the best system devised by man, but it is most expensive as farmers alone cannot do it,without state aid. Because of the high capital and operating costs, irrigation agriculture is most expensive. The yields per unit of water must be high, which usually requires intensive use of land. If water is spread on too much land, a very large percentage of water will be lost through seepage and useless evapotranspiration.

The potential evapotranspiration during the growing season, the permeability of the soil, the quantity of water released and the salt tolerance of the crops are, important. Water for irrigation can be gathered from a large or infertile area, to be used on a relatively small fertile area, or water in excess of evapotranspiration, during the wet season, can be stored for use during dry months of the year. It may be stored either on the surface behind dams or bunds or underground, usually in porous alluvium or limestone.

Hot springs

When we speak of water, we cannot omit to mention the hot springs found in Sri Lanka. The most famous are the hot wells at Kinniya on the Trincomalee-Anuradhapura highway. These wells have some difference when compared with hot springs at Mahapelessa, Komana, Maha Oya and Thumpolanchola. There are some at Wellassa.

The wells at Kinniya have a special significance connected with the Hindu god Ganesha with an elephant head. There is also the mythical conception that king Ravana had hidden Sita in the wilderness of the wells.

People believe that there is a therapeutic value in the water founding the hot wells at Kinniya, and the thermal energy of the 7 wells differs from one to another. They are within an enclosure about 36 ft. long and 16 ft. broad. No. 1 is about 3 ft. deep, No. 2 about 4 ft., No. 3 about 6 ft., No. 4 about 1 ft., and so with No. 5, No. 6 about 3 ft. deep and No. 7 about 2 ft. deep. The wonder is that there are fish in the wells. According to balneology, these wells are said to contain healing powers, specially in curing rheumatic disorders and skin rashes. These are similar to the hot springs in Georgia, US, known for their medicinal value. People bathe in these waters in order to benefit from their high mineral content.

Drilling wells

Underground water may also be brought to the surface by drilling wells. Once a well is dug, there may be sufficient pressure to push the water to the surface, in which case, they are called 'artesian' wells. These wells are found in Sri Lanka too where tap water is not available, or where wells go dry. The common way is to use wells to draw up water by means of a rope. In the rural areas, every house has a well, and there are also public wells for drinking and bathing purposes.

Water is used in Sri Lanka for the production of hydro-electric power to supply the national grid. But, due to the great demand for electricity, thermal power is added to supplement in meeting the requirement. During dry season, due to lack of water in dams, power-cuts are often implemented to meet the short supply.

Hydro-electricity in Sri Lanka is the brainchild of the engineer D. J. Wimalasurendra. He was given the idea of hydro-power, while he was travelling to Diyatalawa, along with a few Boer prisoners, who happened to be engineers. The waterfall came to be known as 'Laxapana' because it was believed that its hydro potential could light 100,000 lamps.

Sri Lanka is lucky to have an abundant supply of water for domestic and other uses. Few dams of recent construction have contributed much of irrigation purposes, whilst supplying hydro-power as well.

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