Irrigation
the process of watering or moistening land by ditches or other artificial means. It is probably the earliest application of science to agriculture. During the last half of the 19th century the lands watered from the ancient irrigation works of India were more than trebled by the completion of the Ganges canal system, the largest and costliest in the world, and by the more systematic and effective operation of works previously built. The land reclaimed and the value of the products of irrigation in the historic Nile valley have been largely augmented with the completion of the great dam at Assuan, at a cost of $24,000,000. Since the construction of the first ditches in Utah by the Mormon pioneers, irrigation has marvelously extended the domain of enterprise and civilization in all parts of the world. It has wholly changed the appearance and prospects of the W. third of the United States. It promises to make the Northwest Provinces of Canada one of the grain fields of the British empire. The irrigated farms of the Australian provinces of Victoria and New South Wales already rival, and will in time surpass, in value the livestock industries which were first established on the arid plains of that continent. Within the past quarter of a century irrigation has made the Hawaiian Islands one of the chief sources of supply for the IRRIGATION sugar consumed in the United States. vesting. In the distribution of water It has increased the population and agricultural wealth of New Zealand and been greatly extended in Mexico and Central America.
Methods. The water used on the greater part of the irrigated area is distributed by gravity. The supply is tapped at a point higher than the land to be watered; thence it is carried in canals or ditches, which follow the contour of the country, to the place of use. Many of these canals are important engineering achievements. The Cavour Canal, in Italy, cost over $17,000,000, and has doubled the population of the valley of the Po in the past 40 years. The Ganges Canal is the greatest system in India. The upper Ganges has 890 miles of main channel, 3,700 miles of laterals, 282 miles of outlet channels, 31 locks, 202 bridges, and 17 dams. It was completed in 1884, irrigates 1,205,000 acres, and cost $14,644,000. The lower Ganges system embraces 531 miles of main canal and 1,854 of lateral canals. It irrigates 620,000 acres, and cost $7,- 000,000. The W. Jumna Canal, begun in 1875, has cost over $8,000,000, and has a total length of 1,200 miles. In the United States there are several canal systems, and at Lagrange, California, is the highest overfall dam in the world.
The lifting of water from wells streams by hand or by oxen was one of the great means of ancient irrigation.
In recent years this has been supplemented by an important use of steampumping plants. There are 1,500 of these in the San Joaquin valley of California alone. A large part of the water used in the irrigation of cane in the Hawaiian Islands is raised by pumps.
Some of these are of extraordinary size and capacity, being capable of lifting 20,- 000,000 gallons 500 feet vertically in 25 hours. The method of distributing water from canals must vary according to the amount of water available, the nature of the soil, the topography of its surface, and the character of the crop, and there can be no single best method under all circumstances. or Flooding. Under the flooding system small parallel ditches are constructed about 100 feet apart, the plans varying with the slope of the ground. These small ditches are usually fed from a lateral from the main canal. Where the surface is broken, they will be irregular in outline, and will generally approximate a right angle to the steepest slope of the soil. They are usually simply furrows made with a heavy mould-board plow, and where the crop is grain they are filled back by the plow before har- IRRIGATION they are cut at convenient points to allow the water to run out and spread over the surface. The water thus released if left alone would follow the lines of quickest descent, and in doing so spread out as it proceeds, dividing into numerous branches or rills as it increases its distance from the opening of the ditch.
For the purpose of facilitating its spreading and to insure its application to every portion of the surface, the irrigator follows its course and guides it by moving a few shovelfuls of earth here and there, thus separating the various small rills and starting the branches in different directions. This is a cheap but somewhat disagreeable method, because the irrigator has to work in the water and use all his strength and speed in order to direct the water so that it will reach all points, which it seldom does in equal volume. It has for its chief claim cheapness and speed, but sacrifices economy. Under this system an experienced irrigator can cover from 10 to 20 acres a day, the area depending on the character of the land, the uniformity of the surface and the volume of water at his disposal. For such crops as grain, alfalfa, clover, and the various grasses, and for everything which is sown broadcast and is distributed uniformly over the surface, the flooding system is employed.
Checks. A modification, and in some respects a great improvement, of irrigation by flooding consists in the use of what are called compartments or checks.
It is really flooding by the use of levees, which restrict the movement of the water to definite areas, thus giving assurance that it shall remain on this area till it sinks out of sight or is drawn off.
The compartments or squares vary in size according to the slope of the ground and with the locality. The Mexican irrigators in the S. W. make compartments less than 100 feet square, while in California and Arizona they often contain several acres.
Furrow Method. - Under this method parallel furrows are plowed which lead from the lateral used across the rows of crop to be irrigated. A small opening is made in the ditch to let the water between each of these rows. There are numerous devices for regulating the turning of water into the furrows from the field lateral, the simplest being the placing of a dam of canvas or earth below the opening through which water is to be run; but in many places the lateral is constructed permanently, often consisting of a plank or cement flume with openings in its side, having ad- IRRIGATION justable gates by which the amount of by evaporation, distributing water at water delivered to each furrow can be regulated. In the application of this water the attention of an irrigator is required to see that the proper amount is kept in each furrow, and that it does not break out and flood the surface, leaving the furrow beyond the break without moisture. The success of this system depends on having a soil in which vertical percolation is not excessive and lateral movement is adequate. The furrows must be so constructed as to maintain the velocity of the water within the safe limit permitted by the character of the soil; otherwise there will be an injurious erosion of the furrows. Where these conditions are secured it has several advantages; it thoroughly soaks the soil and accomplishes the distribution of moisture without saturating the surface and causing it to run together, as it does where water stands on it. In cultivating crops the displacement of the soil is reduced to a minimum; hence, the labor is reduced and the cost is less than by any method which distributes water so evenly and thoroughly. There is less loss from evaporation because a less area of water is exposed to the action of the air and sun.
Subirrigation. Introducing water below the surface for the watering of crops has several obvious theoretical advantages, such as the preventing of loss IRRIGATION levels which will encourage plants to strike their roots deep deep in the soil, and the reducing of frequent quent surface cultivation, which have caused inventors and cultivators to labor to secure a system which would be effective and cheap enough for general adoption, but thus far without complete success.
Irrigation Laws and Institutions. In France, Spain, Italy, Egypt, and India all the more important irrigation works are owned and controlled by the government. In Italy, especially, irrigation is highly developed. Most of the water for irrigation purposes is drawn from the Po river and from lakes Maggiore and Como. In undeveloped and sparsely settled countries like Australia nearly near all that has been done is the result of private enterprise. In Canada all streams are state property and all irrigation works are built under licenses issued by the government, and in accordance with the plans prepared or approved by it.
The Reclamation Service in the United States, operated by the national government, was established by the Reclamation Act of June 17, 1902. By 1920 some 3,000,000 acres of land located in semiarid and arid regions had been made valuable both from the standpoint of agriculture and of homesteading. The irrigation projects are in Ariz., Cal., Colo., Idaho, Kan., Mont., Nebr., Nev., N. M., State Project Estimated area on Gross cost completion Acres Dollars Arizona Salt River 192,077 15,106,943 Arizona-California Yuma 110,000 9,495,570 Orland 20,533 1,048,298 Colorado Idaho Grand Valley 50,000 3,545,157 Uncompahgre Valley 100,000 7,341,651 Boise 327,552 12,758,216 King Hill 16,385 591,362 Minidoka 121,392 5,998,863 Huntley 32,885 1,750,943 Milk River 181,000 5,955,475 Montana .
Sun River 174,620 3,775,096 Blackfeet 118,500 1,048,250 Flathead 134,500 3,761,877 Fort Peck 152,000 704,534 Montana-North Dakota.
Nebraska-Wyoming Nevada New Mexico New Mexico-Texas North Dakota Oregon Oregon-California South Dakota Lower Yellowstone 59,613 2,915,090 North Platte 251,715 10,643,517 Newlands 231,000 6,384,544 Carlsbad 24,991 1,383,458 Rio Grande 162,000 9,775,296 North Dakota Pumping 26,151 721,163 Umatilla 36,300 2,473,191 Klamath 141,444 3,092,101 Belle Fourche 97,889 3,479,802 Utah Strawberry Valley 60,000 3,506,004 Okanogan 10,099 947,029 Yakima:
Washington Storage unit 3,783,105 Sunnyside unit 110,828 3,355,599 Tieton unit 32,000 3,380,284 A Jackson Lake enlargement 783,153 Wyoming Total Riverton 100,000 71,918 Shoshone 136,618 6,109,061 3,212,092 135,686,549 IRRITABILITY N. Dak., Okla., Ore., S. Dak., Utah, Wash., Wyo., Texas. The funds for this work come mainly from the sale of public lands and from oil-leasing royalties. According to the Reclamation Extension Act of Aug. 13, 1914, the money expended is returned to the fund by the settlers, through payments in fifteen or twenty annual installments, without interest. Over 400,000 persons are living on the 1,780,000 acres irrigated by the Reclamation Service.
The value of the crops in 1920 on the project land was nearly $114,000,000. In 1902 the average value of the desert land was not more than $10 per acre. Since the government has undertaken the irrigation of this territory, the average value has increased to $200 per acre, or a total of over $350,000,000. More than 13,000 miles of canals and ditches have been built on the projects. The Reclamation Service in 1920 served 2,845,000 acres of land, including 1,662,000 acres for which the government furnished the total water supply, and 1,183,000 acres to which the government sent stored water as an aid to the supply of private streams. The Mexican Government has taken an interest in the question of irrigation, and has appropriated over $20,000 to be used for the improvement of the Yaqui River Valley, Sonora. The table on page 199 shows the principal United States irrigation projects and their cost up to June 30, 1919. a