It should be borne in mind that the object of land drainage is not only to remove the surplus water, but to promote a free and natural circulation of water in the soil, and to allow the mineral constituents of the water to reach the plant roots.
In the drainage of buildings, glazed socketed stoneware pipes are used, varying in diameter from 3 to 9 inches, laid straight in plan and in longitudinal section, and laid to falls, calculated to give a minimum velocity of 3 feet per second when flowing half full. These are laid in trenches, with inspection chambers at all changes in direction, and should be laid on and surrounded with concrete. In bad ground, or under dwelling houses, cast-iron pipes are employed, with special turned and bored joints. In towns these drains lead into the public sewers, which are similar stoneware pipes from 6 to 18 inches in diameter, larger sizes being constructed in brickwork or concrete, and either circular or egg-shaped form. In populous areas these sewers attain very large dimensions, the northern outfall sewers of London consisting of five parallel sewers, each 9 feet in diameter. See Draining.—Bibliography: G. S. Mitchell, Handbook of Land Drainage; Moore and Silcock, Sanitary Engineering; Gilbert Thomson, Modern Sanitary Engineering.
Drainage Tubes are fenestrated india-rubber tubes used in surgery to effect the gradual removal of the contents of a suppurating cavity. The inner end of the tube is in the cavity, and the outer end projects above the skin surface, and is usually fixed by a stitch or safety-pin, and covered with suitable dressings.
Draining, in agriculture, a method of improving the soil by withdrawing the superfluous water from it by means of channels that are generally covered over. Plants cannot thrive unless there is free circulation of air and water round their roots. The successful practice of draining in a great measure depends on a proper knowledge of the superficial strata, of their situation, relative degrees of porosity, &c. Some strata allow water to pass through them, while others more impervious force it to run or filtrate along their surfaces till it reaches more level ground below. In general, where the grounds are in a great measure flat and the soils of materials which retain the excess of moisture, they require artificial means of drainage to render them capable of yielding good crops whether of grain or grass. The wetness of land, which makes it inferior for agricultural purposes, may appear not only as surface-water but as water which flows through the lower strata, and to draw off these there are the two distinct operations of surface-draining and under-draining. The rudest form of open drains are the deep furrows lying between high-backed ridges, and meant to carry off the surplus water after the soil is completely saturated, but in doing so they generally carry off also much of the best of the soil and of the manure which has been spread upon it. The ordinary ditch is a common form of water-course useful in certain cases, as in hill pastures. But covered drains at a depth of 4 feet or so are the common forms in draining agricultural lands. They are generally either stone-drains or tile-drains. Stone-drains are either formed on the plan of open culverts of various forms, or of small stones in sufficient quantity to permit a free and speedy filtration of the water through them. The box-drain, for instance, is formed of flat stones neatly arranged in the bottom of the trench, the whole forming an open tube. In tile-drains, tiles or pipes of burnt clay are used for forming the conduits. They possess all the qualities which are required in the formation of drains, affording
a free ingress to water, while they effectually exclude earth, as well as other injurious substances, and vermin. Drainage tiles and pipes have been made in a great variety of forms, the earliest of which, since the introduction of thorough draining, was the horse-shoe tile, so called from its shape. These should always rest on soles, or flats of burned clay. Pipe tiles, which combine the sole and cover in one piece, have been made of various shapes, but the best form appears to be the cylinder. An important department of draining is the draining off of the waters which are the sources of springs. The judicious application of a few simple drains, made to communicate with the watery layers, will often dry swamps of great extent, where large sums of money, expended in forming open drains in the swamp itself, would leave it but little improved. In the laying out of drains the first point to be determined is the place of outfall, which should always afford a free and clear outlet to the drains, and must necessarily be at the lowest point of the land to be drained. The next point to be determined is the position of the minor drains. In the laying out of these the surface of each field must be regarded as being made up of one or more planes, as the case may be, for each of which the drains should be laid out separately. Level lines are to be set out a little below the upper edge of each of these planes, and the drains must then be made to cross these lines at right angles. By this means the drains will run in the line of the greatest slope, no matter how distorted the surface of the field may be. All the minor drains should be made to discharge obliquely into mains or submains, and not directly into an open ditch or water-course. As a general rule, there should be a main to receive the waters of the minor drains from every 5 acres. The advantages of drainage are obvious. In the first place it brings the soil into a more suitable condition for the growth of plants, aiding in producing the finely divided and porous state which allows the roots and rootlets to spread themselves at will in order to obtain the needed supplies of food, air, and moisture. It also allows the sun's rays to produce their full effect on the soil and plants. In the presence of stagnant water a great part of this effect would be lost. See Drainage.
