IRRIGATION How Egypt Gets its Water for Irrigation.—In all parts of the world where there is a long dry season irrigation is practiced, but it is most important in monsoon and especially subtropical regions. Forty or fifty centuries ago in the days of the ancient Egyptians and Baby lonians it had already reached a high stage of development. In Egypt nature makes it remarkably easy to practice irrigation On a large scale. The White Nile or main stream comes from three of the great lakes of Central Africa which serve as reservoirs and give a large supply of water at all seasons. The Blue Nile and the Atbara. come from the highlands of Abyssinia and are subject to great floods which cause the river to overflow its banks during the summer. Thus at that season the river not only waters the land without exertion on the part of the farmers, but fertilizes the fields with rich alluvium. In order to equalize the flow of water and make irrigation possible at all seasons the great Assuan Dam has been built.
Some of India's Irrigation Projects.—In India one single irrigation project on the Chenab, a tributary of the Indus, waters 2,500,000 acres and supports a million people. The Chenab Canal was built by the British government to increase the production of grain and relieve the severe overcrowding in other parts of India. Before any land was assigned to settlers the fields, streets, and village sites were all laid out in what was then a desert. Places for the post office, bazaars, and government offices were assigned, and everything was ready. Then 800,000 people poured in within eight years. The canal cost nine million dollars and to-day the crops each year are worth about twelve million. Since ancient times southern India has been full of "tanks" or small ponds built for irrigation. In recent decades all sorts of clever schemes have been devised for bringing water from places where it is plentiful to those where it is scarce. For instance, the Cardamom Mountains at the southern end of the western Ghats receive 80 or 100 inches of rain and the plains to the east only 20 or 30. Accordingly the Periyar River draining these mountains on the wet west side has been made to flow through the mountains in a tunnel a mile long. Emerging on the east side it
waters the dry plains near the city of Madura.
Irrigation in the United States.—The people of the eastern United States rarely realize the importance of irrigation, for in the entire country only one farm in forty is irrigated. Nevertheless in the western part one million people live on fifteen million acres of irrigated land.
The distribution of this land is illustrated in the following table: The first column of figures shows what percentage of the total area of each State is included in irrigation projects. These projects include over two-thirds of the 45,000,000 acres which may possibly be irrigated some day. As yet, however, they have been developed only to the point where about half of the area included in them re ceives water. The second column shows what percentage of all the farms are irrigated. In such a State as Arizona, even though the splendid Roosevelt Dam waters 270,000 acres, there is not water enough to irrigate more than 1 per cent of the total area, and only about one-half of 1 per cent has thus far been utilized. This small fraction, however, includes 53 per cent of the farms in the State. The remaining 47 per cent are mostly cattle ranches, and will prob ably never be irrigated.
California is much better off than Arizona. It possesses enough water so that 51 per cent of the land will probably be irrigated before many years. Moreover, among the 55 per cent of farms which are not irrigated a large number are wheat ranches, many of which are of uncommonly large size. The largest single irrigation project in California is in the Imperial Valley. There the waters of the Colorado River, which till 1900 flowed unused through a desert, now support some of the richest farms in the United States. This region closely resembles Mesopotamia and Egypt, and raises certain crops such as dates, the silky Egyptian cotton, and rare varieties of melons which grow almost nowhere else in the United States.