« AnteriorContinuar »
invested, and yielded a large profit, though it was often obtained indirectly. India has the largest reservoir in the world. It covers an area of 21 square miles, and it was constructed for irrigating in Rajputana. It is known as the great tank of Dhebar.
Irrigation in the United States.-In America, the town-building Pueblo Indian tribes practiced irrigation perhaps a thousand or more years ago. Their ditches and canals can still be traced in the little valleys near the mesas of southwestern Colorado and adjacent portions of Utah, Arizona and New Mexico, where the cliff dwellings are found, as well as across the border valleys through which are scattered numerous ruins of community dwellings. Their knowledge of engineering is evident, and remarkable. Careful levels have been run over several miles of their canals. The grade was found to be fairly uniform and suited to a canal of sucli dimensions, as well as in accord with present day knowledge of hydraulics, safe velocities and coefficients of friction. While these well defined remains of ancient irrigation works have long outlived the civilization to which they belonged, there are cases where they have been utilized in modern works. The ditches at Las Cruces, New Mexico, have been used uninterruptedly for over 300 years. Some 70 years before the settlement of Jamescown, the Spaniards irrigated on the Rio Grande. Adventurous. mission fathers pushed on to California, carrying the art of irrigation with them.
The beginnings of irrigation by English-speaking people in this country were in the Salt Lake valley of Utah, in July, 1847. The Mormon pioneers, driven out from Illinois and Missouri, stopped from necessity on the shores of the Great Salt Lake. They diverted the waters of the little canyon streams upon the present site of Salt Lake City, so that they might raise a crop from the very last of their stock of potatoes and save the band from starvation. At about the same time water for irrigation was drawn from the ditches used for placer mining by the gold miners of California. After the stoppage of hydraulic mining by the passage of anti-débris laws, the ditches were either abandoned or used exclusively for irrigation, Many were enlarged and are still used.
The Extent of Wheat Irrigation in 1899 is shown in the table below:
While considerable wheat is irrigated in some states, practically all that is grown in them, yet the average per cent of irrigated wheat in all the irrigating states is relatively small, only 14 per cent. Excluding California and Washington, where much wheat is raised and little irrigated, this rises to 36.5 per cent; 17.7 per cent of the wheat produced is irrigated, compared to 14.1 per cent of the acreage. On this basis which, however, takes no account of differences in soil, rainfall and climate, the yield in these states would be increased over 25 per cent if all the wheat were irrigated.
The Problems of Irrigation in our country are, and have been, along two general lines: Agricultural and engineering; and legal and social. Of these two lines, the latter has presented the greatest difficulties. Litigation and controversy have been a menace and a source of loss to many communities because no institutions existed for adequately defining, limiting and protecting water rights. The claims of navigation came into conflict with those of irrigation. When streams flowed through more than one state, interstate difficulties arose. Some of these are the basis of a suit by the state of Kansas against the state of Colorado.
Work at the solution of either class of problems has been immensely handicapped by a most lamentable lack of knowledge
1 12th U. S. Census, 6:825-870.
of certain essential facts and conditions. Among these are existing water supply, quantity required to grow crops, losses from seepage and evaporation in distribution, character of the control over streams already vested, and measures of administration requisite for an equitable and effective division of water supply among a multitude of users. Such unforeseen results as alkali lands and seepage waters, formerly secondary considerations, are now often the most primary problems. Such irrigation as could easily be accomplished with simple means independent of co-operative institutions has largely been effected. As the work extended, greater problems arose, claims became hopelessly conflicting and united effort under institutional administration became an imperative condition of advantageous development.
Water Supply.—There are two sources of water for irrigation: Surface waters, such as streams and lakes, and subterranean waters. The former supply over 90 per cent of the irrigated land. There are three ways of obtaining underground waters: By pumping from wells; by driving tunnels into the sides of hills and mountains; and by using flowing wells. Artesian areas are widely scattered, and individually they are of small size, except in the Dakotas and California. In 1889, 51,896 acres, or 1.4 per cent of the irrigated land, were irrigated from wells. In 14 irrigating states there were 8,097 wells, nearly half of which were used in irrigation. Each well supplied on an average 13 acres, had a depth of 210 feet and discharged 54 gallons per minute; 169,644 acres were irrigated from wells in 1899. Underground waters seem to be present very generally. It is claimed that there is not a farm of 160 acres upon the great plains region without the requisite moisture absolutely needed for from 10 to 30 acres of tillable ground.' The average depth of water applied to crops in 1899 was 4.35 feet, and in 1900, 4.13 feet.
Application to Crops.—The two principal methods of irrigation are by flooding and through furrows. The former is generally used in growing grain. There are two methods of flooding, the check system and by wild flooding. By the latter process a level field is completely submerged. When the ground is not level enough for this, the field is divided into compart- 1 Hinton, Rept. on Irriga., Cong. seriai No. 2899, part I, p. 8.
ments by ridges. The highest compartment is flooded to the top of the ridge, which is then opened on the lower side. The water thus passes into the next compartment, and this procedure is continued until all the compartments are irrigated. If the land is properly prepared and irrigated before the wheat is sown, two subsequent irrigations will make a good crop. When the soil is thus used as a storage reservoir, in parts of Kansas and California no irrigation is needed between planting and harvesting.
Alkali.—Arid region soils are usually rich in mineral ingredients. This is because such soils originated in the de
composition of rocks in regions where the rainfall is too scanty to wash out the soluble elements as in humid regions. The soluble salts are naturally distributed throughout the soil, and are not harmful until the application of irrigation water. They are then leached out of the higher grounds and concentrated in the lower lands. Evaporation tends to bring them to the surface. Many irrigation waters also contain much salt in solution, which results in a further deposition of salt. The result of these factors is often ruinous to vegetation. Many thousands of acres have been thus rendered unfit for cultivation in the United States, and the agricultural industries of 59 villages in India were wholly or partly destroyed by the rise of
alkali previous to 1864. Water containing over 1,000 parts of salt in a million has been used without injury. Most of the artesian wells of Dakota have a salt content much higher than this, and the effects of irrigating three or four years with this water rendered wheat lands of the Red river valley almost wholly unsuited to raise current crops. The most effective method of removing alkali from land is by underdrainage and flooding.
The Cost of Irrigation in the United States as shown by the eleventh and twelfth census is as follows:
Average values per acre 1889
1899 Irrigated land
$42.53 Water right ....
26.00 Annual cost ....... ............ 1.07
0.38 First cost of water rights .......... 8.15
7.80 A rise in values would be expected, instead of a fall, as good lands with water supply were scarce in 1899, and those lands were first irrigated which required least labor and capital. It has been estimated that a perpetual water right in a grain country is worth from $25 to $50 per acre. The cost of irrigation from many of the original ditches was as low as $2 to $5 per acre.
The Semi-Arid Region of the United States. There are men still living who knew the Mississippi valley as a wilderness. For several generations a popular American slogan has been bowestward the course of empire takes its way," and the rapidity with which the fertile lands of the great river valleys were brought under cultivation has been almost incredible. As this * huge wave of immigration swept across the prairie to the great plains, it encountered the subhumid belt as a buffer between the lumid and the arid regions. Gradually the settlements proceeded westward from the abundantly watered Mississippi and lower Missouri valleys, and pushed into the well defined subhumid slope which rises progressively toward the Rockies. These virgin lands, bordering upon the greatest wheat raising region of the world, and fully as fertile, since they were not washed by frequent rains, were a continual temptation to
1 Mon. U. S. Geol. Sur., 25:546-547.
2 Indus, Com, 10:xxxii.