CHAPTER X

IRRIGATION

Since ancient times, irrigation has been practiced in semi-arid and arid countries. Applying water to growing crops by carrying it out into the fields through ditches and allowing it to spread over and percolate into the soil, has assumed immense proportions in the more arid regions of the United States. Even in the states further east than the Mississippi river, irrigation is found very profitable under some conditions. The national government has inaugurated a very large scheme of co-operation in which, through an organization called the Reclamation Service under the Department of the Interior, it joins with many landowners and aids prospective purchasers of public lands in the construction of immense systems for irrigation. In some cases canals are built taking water directly from streams to the land. In many cases dams are necessary to raise the level of the water in the streams from which the water is drawn. In other cases immense dams are made to create great storage reservoirs in which supplies of water are accumulated to be used when the crops most need them. The United States Department of Agriculture also is doing much in co-operation with private parties or organizations who are irrigating lands. This department is aiding not only in making plans for irrigation plants both by the gravity plan, and by pumping by wind or other power, but it is also studying methods of distributing the water to the farmers and to their crops, and is investigating methods of farm management under irrigation. The engineering plans being worked out by the Reclamation Service alone involve many millions of dollars and with the co-operation of the United States Department of Agriculture

will make many thousands of irrigated farms available for farmers. Care is being used that these lands may be divided into family farms and thus made to serve well the largest possible number of people and to increase the number of America's farm homes. This constitutes the most extensive irrigation scheme ever undertaken, and is one of the most ambitious engineering feats ever entered upon. It is a public enterprise which will again prove the ability of a republican form of government to

carry out large national movements which benefit the whole people. Through this work the United States government is extending its policy, inaugurated through the national homestead law, of dividing the land into family farms.

Not only is irrigation profitable in arid and semi-arid countries, but also in countries where the rainfall is not evenly distributed throughout those months in which crops make their greatest growth. Irrigation on a large scale is practicable only where streams, lakes, rivers,

Figure 138. Windmill and storage reservoir for irrigation water.

artesian wells or artificial storage reservoirs furnish large supplies of water. Someone has illustrated the limitations of irrigation in the great arid West by comparing the whole droughty plains and intermountain areas in which the rainfall is light to a twenty-acre field with one furrow plowed across it, the furrow representing

that proportion of the whole for which the water is available for irrigation. The semi-arid area on which dryland farming must be carried on is very extensive, and farm management there must be planned to conserve, for the use of crops, the small amount of water annually precipitated. In many places the windmill, or steam or gasoline engine to pump water from wells upon limited areas, as near buildings, will help make possible the development of a homelike farmstead on large ranch-like

farms in semi-arid regions, and will give some food for man and beast, even in the exceptional years of least rainfall, and will help make the farm pay in all years.

In regions like Minnesota, on the other hand, the many streams, the thousands of lakes, the large quantities of available well water, the less amounts of water required for irrigation where the rainfall is nearly sufficient, and the possibility of storing surface water in large artificial reservoirs, will make it comparatively easy to irrigate large areas of land. Good lands have been so cheap that farmers and gardeners have only begun to appreciate the fact that at no distant date the higher price of lands, together with the cheapened machinery and possibly cheaper labor, will make irrigation profitable in many places where the rainfall has been heretofore wholly depended upon.

Sources of water.-The bulk of irrigation is now done where the water is obtained from mountain streams or rivers so situated that the water may be led out, by means of canals and ditches, to lands which are nearly level, in the valley lower down the stream. These ditches are usually laid out with a very gentle slope, through the low lands or around the borders of the hills. Branches from the main canal are led off to the various tracts of land to be irrigated, where the ditches are further branched and the water carried to the farms and fields. In many cases, lakes and reservoirs are employed in which to store up flood water for use during the dry season when the water in the streams is low. In other cases, the storage capacity of lakes has been very greatly increased by means of dams across their outlets.

Storage reservoirs are being made in many places by building dams across valleys, thus conserving large quantities of water which can be led out and spread over the fields in times of drought. As a rule, these