IRRIGATION.
Wasserung, . . GER. I Regamiento, . . . IT.
Befeuchtung, . . „ Generous as the Indian soils usually are and favourable as arc the seasons in the plains and valleys of British India, the amount of the rain fall, one year with another, varies by fifty per cent. above and below the average. Rain is frequently absent for many weeks, and without some artificial means of supplying the soil with moisture, no crops could at those periods be taken off the ground. Something can be grown with water, nothing can be obtained without it ; and throughout the south and east of Asia the efforts of the rulers and the people have been directed to obtain and hoard the water supply. Of the seven regions into which British India has been divided for hygrometric purposes, two only have their fill of water from natural sources. In tho drier regions the rainfall is precarious as well as scanty, and wide expanses of good soil lie permanently unfilled and tenantless. A good part of the I'aujab and the whole of Sind would be scarcely habitable without irrigation, and in the south eastern quarter of the Madras Presidency it is in dispensable. The natives of these regions have, from unknown times, been forming tanks, digging canals, and leading off channels from rivers, some of them betokening great skill and great labour ; and in the 18th and 19th centuries the labours of British engineers, especially of those of the Madras Presidency, have been conspicuously successful in irrigation. Sir Arthur Cotton, in Tanjore, re constructed and enlarged the ancient irrigation works with such effect, that during the first six teen years 50,000 acres of land, previously waste, were brought under tillage, the average produce per acre was increased by one-eighth, and the selling value of the land was doubled. In the delta of the Godavery, where Sir Arthur Cotton next went, notwithstanding its rich alluvia] soil and fostering climate, alternate flood and drought had brought famines. The territory is now a luxuriant garden, 265,000 acres having been brought under humid cultivation, and the population is prosperous. The Ganges Canal,
which diffuses irrigation over an area 320 miles long by 50 broad, is the most magnificent work of its class in the whole world, having' a main channel 348 miles long, primary branches of 306 miles, and minor arms of an aggregate length of 3000 miles. In one place this canal is carried over a river 920 feet broad, and thence for nearly three miles along the top of an embankment 30 feet high.
The irrigation canals of the Tigris and Euphrates have not retained their ancient magnificence, but the oases around Bokhara and Khiva owe their value to the irrigation channels led from the Oxus. In Persia, Karez aqueducts are largely in use for irrigation, and the Nizam Shah dynasty of Ahmadnaggur formed several of these on the north of their capital.
In India, irrigation is carried on from wells and from tanks, and largely from channels led from its rivers, well irrigation being employed for garden culture, and to supplement the rainfall. The efforts made by several of the races to pre serve and utilize the water from the rains and rivers, have been gigantic, as in the cyclopean Gorbasta structures of Baluchistan, where dams of huge stones have been drawn across the valleys by a race of whose history nothing is known. In India both Hindus and Muhammadans have made great artificial lakes, with dams or bunds, often highly ornamental. One of the most beautiful is that of Kankroli or Bajnagar in the Mewar or Udaipur State. Its retaining wall is about 2 miles long, and the area is about 12 square miles. It is 376 paces in length, is covered by white marble steps,—a fairy scene of architectural beauty.
The great tank at Cumbum, in the Ceded Districts, is 8 miles in circumference, and covers an area of nearly 15 squares miles ; that at Ulsoor, near Bangalore in Mysore, is of equal size. The magnificent lake constructed by Mir Alain, near Hyderabad in the Deklian, as a famine work, has a steamer on it.