Fig. 572. Two systems of laying out drains. themselves find it difficult to secure men who have the patience, the feeling of responsibility and the practical skill to do the work well. But while the farmer should be discouraged from attempting the drainage of large and difficult areas on his own place, it is important for him to have a clear conception of the general principles of drainage and of what constitutes good detail practice

In regard to the size of tile, it is doubtful whether it is ever desirable, even with laterals, to use sizes smaller than 3 inches, except it be in cases when the fall is large and the soil close. When

Fig. 575. Laying tile from the top of

the ditch by means of a tile-hook (tool shown at left in Fig. 578).

single lines of drains are laid, to remove water from low places, larger sizes should be chosen than would be required in large areassystematically treated, because in such cases more surface water from the surrounding higher lands, relatively, must be cared for by such drains. The greater the fall the smaller the tile may be; and doubling the gradient increases the carrying capacity of a given size nearly When one-third. other conditions are the same, the capacity of tile increases somewhat faster than in proportion to the squares of their inside diameters.

In determining the proper sizes of mains for the drainage of a given area, so many purely local considerations must be taken into account that specific rules that may be safely followed cannot be given. Examples of special cases will best serve the purpose. Figs. 567 and 571 represent drains laid out under the supervision of C. G. Elliott. The soil in each case is a rich black loam with yellow joint clay subsoil. The surface is nearly level, interspersed with basin-like ponds that are 12 to 24 inches lower than the surface surrounding them. The size of the mains and laterals in Fig. 571 is indicated and their distance apart may be found by applying the scale. The least grade used is 1 inch fall to 100 feet. The largest main is 7 inches in diameter and furnishes an outlet for a deep pond into which surface water gathers rapidly, requiring more ample outlet than an equal area of level field. The soil being open, nothing less than 4-inch tile is used on either of the farms represented in the two maps.

We also give in the form of a table, from Mr. Elliott, the sizes of outlet drains for specific cases

Fig. 574. A compound system of lateral drains.

If double the amount of water were required to be removed from an acre in the same time used in the table, the areas that the different mains would be able to serve would be only half the number stated; while, if the amount of water were half that stated, the number of acres that could be served would be twice as large.

Laying out systems of drains.

In laying out systems of drains the object is to secure thoroughly efficient drainage with the least cost. To do this, it is necessary to avoid laying lines through areas already sufficiently drained; to make the outlet junctions as few as possible; to avoid the use of unnecessarily large tile, and of digging more deeply than is required for good drainage. In Fig. 572 two systems of laying out drains for an area of about 14 acres are represented. By the system A, 625 feet of 4-inch, and 3,020 of 3-inch tile are required, while by that of B only 550 feet of 4-inch, and 2,830 feet of 3-inch tile are needed to do the same work, the lines being 100 feet apart in each case. When long lines of tile are required, three systems of laying have been followed; that of A, Fig. 572, and Figs. 573 and 574. In the case of Fig. 573, covering an area 2,000 feet by 900 feet above the line a, there would be required 9,000 feet of 3-inch tile and 9,000 feet of 4-inch with the lines 100 feet apart; but following the B system (Fig.574), it would be necessary to lay only 3,000 feet of 4-inch tile, with 15,300 feet of 3-inch, with a saving of about $33.

Fig. 576. Roots of an elm tree in a

suction pipe in a dug well three

feet in diameter.

Outlets, junctions and obstructions.

Much care should be taken to secure a clear fall at the outlet of a drain, placing it, if possible, where it will at all times be above water. The last 16 feet of the main should be

composed of some material that will neither decay nor be injured by frost. Perhaps the best method is to construct the outlet with portland cement concrete, setting at

the mouth in the concrete, as it is made, vertical iron rods close enough together to prevent the entrance of animals at times when it is dry. Ordinary glazed sewer tile answers very well, and cast-iron water pipe makes an ideal outlet, except in the matter of first cost.

In joining laterals with the main, three methods are in use: first, special junction tile made at the factory; second, perforating the main on the side Iwith the aid of a tile pick and then fitting the lateral carefully into this; and third, perforating both the main and the lateral, letting the lateral rest on top of the main. When the entrance is made on the side it is important that the lateral enter pointing down stream and forming an angle of about 30 degrees.

Fig. 578. Draining tools. A simple

home-made form of water-level at the top, made of iron pipe with water-guage glass in the elbows at the ends.

Care must be taken that no trees or shrubs whose roots seek running water are permitted to grow near a line of tile through which water runs during much of the growing season. The roots of such trees travel long distances to reach running water and will enter a drain and there branch until, through the arrest of silt, the drain becomes completely clogged. In Fig. 576 are represented the roots of an elm tree that entered a dug well 3 feet

in diameter, and grew across to the suction pipe where the vent in it supplied a stream of fresh water whenever pumping was done. In this position they branched and grew, wrapping themselves about the pipe until it formed a mass 10 inches through and more than three feet long. Very many instances are on record where the roots of trees have entered drain tile, and, branching in the manner shown in the illustration, effectually closed them. When it is not permissible to remove the trees, the joints of the tile must be carefully and very firmly bedded in cement mortar.

Draining heavy clay soils.

There are three chief factors which determine the proper distance between underdrains: (1) The freedom with which water may flow through the soil and subsoil toward the drains; (2) the depth at which the drains are placed; and (3) the interval of time between rainfalls sufficiently heavy to produce considerable percolation. It should be clearly understood that it is the character of the subsoil below a depth of two feet, rather than that of the soil, which chiefly determines the rate at which water moves toward and into the drains, and it should be further understood that the subsoil which takes part in the lateral flow of water may be several feet, even 10 or more, below the level at which the drains are laid, provided it is an open sand coarser in texture than the soil itself. When the subsoil is a stiff clay to a considerable depth, 8 to 20 feet, thorough drainage becomes very difficult and expensive because of the fact that lines of tile must be placed relatively nearer together and some

times even deeper in the ground. There are many regions where the depth of the clay subsoil is so great and the texture of the clay so close that there is no other alternative than to resort to surface drains for longer or shorter periods. Proper tillage and a good system of crop rotation more or less effect a deepening of such clay subsoils by developing a checked or crumbled condition of them, and after this condition has resulted underdrainage becomes more effective.

In cases where the surface 2 or 3 feet and subsoil are comparatively open and underlaid by a close, impervious clay, care should be taken to lay the drains at the proper depth and with the proper distance between them and then to fill the ditch entirely with the open porous surface soil in order to facilitate the entrance of water into the drains.

Cost of underdraining.

The cost of underdraining varies between wide limits, depending on the cost of labor, the cost of tile delivered, the depth and distance apart, and whether natural or artificial outlets must be provided. The cost of 5-inch to 7-inch mains laid 4 to 5 feet deep usually ranges from 90 cents to $1.75 per rod, while 3-inch laterals laid 3 feet deep cost 50 to 75 cents per rod, everything included. Literature.

The following references include the more important works on drainage: Farm Drainage, by Henry F. French, 1859 and 1884; Land Drainage, by John H. Klippart, 1861; Land Drainage, by Manly Miles, 1892; Practical Land Drainer, by B. Munn, 1855; Drainage for Profit and Health, by George E. Waring, 1867 and 1879; Practical Farm Drainage, by C. G. Elliott, 1882; Engineering for

Land Drainage, by C. G. Elliott; Drainage of Fens and Moorlands, by W. H. Wheeler, 1888; Irrigation and Drainage, by F. H. King, 1899; Physics of Agriculture, by F. H. King, Chapters XIV and XV, 1901; Drainage Laws of Indiana, 1903; Drainage Laws of the State of Illinois, 1901; Drainage Laws of Iowa; The Farmer's Handbook Containing Laws of Ohio Relating to Agriculture, 1904; Laws Relating to Construction of Drains (Michigan), 1903.

Fig. 579. A traction ditching machine.

IRRIGATION ENGINEERING AND

PRACTICE

By Elwood Mead

Irrigation is the watering of land by artificial means to enable crops to be grown, or to increase production. In some cases, irrigation is a matter of choice; in others, of necessity. In arid lands like Egypt, the ability to use water in irrigation is necessary to the existence of civilized life. When there is no irrigation, there is desert. Irrigation has its greatest reward in arid lands, but its benefits are not confined to regions of scanty rainfall. Rice is irrigated in Java where the annual rainfall is 8 to 10 feet, and in the United States where the annual precipitation is 40 to 60 inches. In England, Germany, France, Switzerland and Italy, irrigation is highly profitable in districts where irrigated and unirrigated fields, side by side, grow the same crops, and it is extending rapidly in the eastern part of the United States among market-gardeners and growers of crops having a high acreage value.

Nor are the benefits of irrigation limited to supplying the moisture needed by crops. There are large areas of land where the chief benefit from irrigation is the control it gives of temperature. Cranberry marshes are flooded to protect them from frosts. In elevated regions, irrigation lessens the danger from summer frosts. The marcite fields of Italy are warmed in winter and cooled in summer by the thin sheet of water which flows over them. The success of this form of irrigation depends on having warm water, which comes either from springs or the sewage of cities and towns. The same is true of a similar kind of irrigation in Beloochistan. Irrigation is also an effective means

of lessening the labor of cultivation and protecting certain crops from the ravages of birds and insects. Rice-fields are flooded at planting to save the seed from being eaten by birds, and later to kill the weeds.

Irrigation is also an important source of fertility. Analyses of the water of the Brantas Delta in Java showed it to contain 0.35 to 0.65 per cent of phosphoric acid, 0.43 to 0.60 per cent of potash, and 0.25 to 0.27 per cent of nitrogen. The soil brought down by the Black Nile and deposited on the lands of Egypt has been the chief factor in maintaining its phenomenal productiveness through a continued and exhaustive system of cultivation for thousands of years. The section of China irrigated from the head waters of the Yellow river has been its granary for ages. Professor Hilgard, Director of the Agricultural Experiment Station of the University of California, estimates that the silt deposited by irrigation, if it is only the thickness of common cardboard, or about of an inch, is equal to two wagon-loads per acre. In many places, the silt deposits are far greater than this. The water of many streams in the southwestern part of the United States often carries 5 per cent of silt. Not all silt deposits are beneficial. There is no fertility in the sand carried down by the glacial streams from the Alps. The tailings from stamp mills have no fertilizing value and often smother young plants. The toxic effects of the poisons carried in the waters from many mills and smelters make it impossible to use these waters in irrigation.

The antiquity of irrigation.

The earliest Egyptian sculptures show water being raised from the Nile in buckets and poured on the thirsty soil. The works along the Nile and the Euphrates have an unbroken historical record which reaches back more than 2,000 years before Christ. The great works of Beloochistan were built by a race whose history is unknown. There are irrigation works in southern India built by the Hindus which antedate the Christian era, while in many parts of the western hemisphere-notably in Peru and the southwestern part of the United States-there are the remains of ancient irrigation works that are evidently centuries older than any historical record. In some countries, irrigation has risen and disappeared with the civilization of which it formed a part. This is true of the irrigation works connected with the Aztec civilization in the western hemisphere. There are evidences of prehistoric irrigation in the Hawaiian islands. Many of the irrigation canals of the Tigris and Euphrates have been abandoned, and few have maintained their ancient importance.

Extent of irrigation.

The countries that have reliable statistics show an aggregate irrigated area of 85,000,000 acres, India having 53,000,000 acres. These statistics do not include Morocco, South and Central America, or any Asiatic country outside of India. The total irrigated territory probably does not much exceed

100,000,000 acres, or a land surface about equal to that of the state of California. The rate at which irrigation is being extended will soon cause a marked change in these figures. More land was irrigated for the first time in the last half of the nineteenth century than in all preceding centuries. The increase in the world's population, the higher standards of living, the improvements in methods of transportation, and the opening up of new markets, are combining to bring about the reclamation of lands hitherto neglected and to increase the productiveness of lands hitherto cultivated. Irrigation is one of the most potent factors in both directions and it is being extended in countries where it has long been practiced, and introduced in countries where it was hitherto unknown.

The area irrigated along the Nile has been doubled in the last fifty years. Four million acres were irrigated from government works in British India in 1850; twenty million acres, in 1900. Although irrigation in Italy dates back to the Roman Empire, the area irrigated has doubled since 1848. Irrigation in Spain dates back to the Moors, yet the area watered at the beginning of the nineteenth century was not half that at its close.

The most significant extension of irrigation, however, has been in newly settled countries. Fifty years ago, less than 100,000 acres of land were irrigated in the United States. Now, over 10,000,000 acres are being irrigated and more than 15,000,000 acres are susceptible of irrigation under completed canals and reservoirs. Within the last twenty-five years, more than a million acres have been brought under irrigation in the northwest territories of Canada, and canals now being constructed will add another million acres to this area. In Australia, New Zealand and South Africa, irrigation has in recent years become an important factor in agricultural production. The government of Japan is extending its use in Formosa. In the ten years ending December, 1901, the government of Java brought approximately one million acres of land under irrigation at a cost of nearly six million dollars.

Division of the subject.

Irrigation is a many-sided subject, but its different relations fall into three general divisions: (1) Irrigation engineering.

(2) Irrigation practice.

(3) Irrigation institutions.

The first of these includes the determination of the amount of the water-supply and the design and construction of works to render it available.

The second includes the methods of preparing land for applying water, the quantity needed by different crops, and the time and manner of its application to secure the best results.

The third deals with the laws and customs which fix the ownership or control of water-supplies and the business and social relations of water-users to each other and to the public. [This topic belongs with the group of subjects that it is planned to discuss in Vol. IV.]

Each of these has a vital influence on the value of irrigated land and on the peace and prosperity of irrigated states. Each needs to be considered by the student of irrigation, by the settler on irrigated lands, or the investor in irrigation securities.

Irrigation engineering.

Canals. Irrigation canals and ditches are usually unlined earthen channels. Those that carry water from the place of diversion to the place of use follow, as a rule, the contours of the country. There is not the same freedom of choice in the location of diversion canals that there is with roads and railroads, for, while the gravity canal may drop, it can not rise. Sometimes the governing point in a canal location is the highest point in the land to be watered. But on some streams, the head-gate has to be located where the water can be taken out. When canals cross level country, the land excavated is thrown on both sides and serves to form part of the canal embankment. When the canals run along hillsides, the earth is usually all thrown on the lower side.

The relation of width to depth of canals has been a subject of much discussion with engineers. When conditions permit, the width should be twice the depth, but it is difficult to fix any arbitrary rule, as so much depends on the character of the soil and the slope of the country. There are few canals in which water is carried to a greater depth than ten feet. Beyond this, the danger of breaks from excessive pressure more than offsets economy in excavation. In some of the rice canals, there is no excavation. All the water is carried above the surface of the ground in a channel formed by the throwing up of two parallel embankments, which in some instances are three hundred feet apart.

The grade of canals should be heavy enough to give a velocity which will keep the canal clean and not steep enough to cause it to scour. To succeed in attaining this is not always easy. The heavy clay soils of Wyoming and Colorado will stand twice the velocity of the light ashy soils of the state of Washington. The mean velocity in earthen channels should not exceed three feet per second in canals carrying one hundred cubic feet per second or more, but a mean velocity of three feet per second in a full canal may be reduced to half that velocity when the canal is half full, causing a current so sluggish as to result in its rapid filling by silt. Inasmuch as many canals carry their full flow for a short time only, it becomes a perplexing problem to adjust the grade so as to give the most effective velocity. A sufficient velocity to keep canals clean has also a tendency to lessen the growth of aquatic plants, which is often a serious evil.

Kutter's formula is generally used to compute the velocity of canals. It is:

fall of the water surface in a given distance divided by that distance; r is the area of the crosssection in square feet divided by the wet perimeter in lineal feet; n equals the coefficient of friction for different sized channels and channels of different surfaces. The values of n, as determined by recent investigations on American canals, are approximately as follows:

n=0.0175 for canals in earth in excellent condition, well-coated with sediment, regular in cross-section, and free from vegetation, loose pebbles and cobbles.

n=0.020 for canals in earth, in good condition, lined with well-packed gravel, partly covered with sediment, and free from vegetation.

n=0.0225 for canals in earth, in fair condition, the wetted surface being lined with sediment, with an occasional patch of minute algæ, or composed of loose gravel without vegetation.

n=0.035 for small ditches having a rough, uneven bed, and for canals in earth in fairly good condition, but partially filled with aquatic plants.

The location of canals in the arid region of the United States is a comparatively simple matter. The mountain ranges give a general direction to the slopes which lie at their base. The rivers that water the plains east of the Rocky mountains have falls varying from seven to fifty feet to the mile. The trend of the country is in two directions— away from the mountains, and toward the streams. If the river has a fall of twenty feet to the mile, and the canal has a grade of two feet to the mile, at the end of the first mile the canal will be eighteen feet above the river and can usually irrigate all of the land between its bed and the stream. Each additional mile increases the difference in elevation and, as a rule, the width of the irrigable strip.

While the location of canals is relatively simple, it is otherwise with their construction. Only engineers familiar with the behavior of arid western soils should be placed in charge of the building of an irrigation canal, because experience is absolutely necessary to taking proper precautions to prevent breaks or excessive seepage losses. Soils that have a large percentage of alkali have a tendency to melt like sugar in water. Gypsum soils are always treacherous material for canal banks. A knowledge of the behavior of these various classes of dissolvable soils is an essential feature in the equipment of the irrigation engineer.

In fixing the carrying capacity of canals, the area of land that is susceptible of irrigation or worth irrigation should be carefully studied. After this, the quantity of water required for the irrigation of an acre should be ascertained and the capacity of the canal based on it. This duty of water should not be fixed by the average requirements of the year, but by the volume needed during the period of greatest use of water. The demands for one month may be double that of any other month, but this month is usually the critical period of the growing season, and a failure to meet