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SURFACE AND UNDERGROUND DRAINS - Part 1

For underground drainage, the tile drain, commonly known as the agricultural drain, is the most efficient form. Pipes, three inches in diameter, are advisable. Cheaper drains are constructed of stones, saplings, and boards. Tile drains will last for generations and are the cheapest in the end. Each tile or pipe, should be straight, hard, smooth inside, and well burnt so as to ring when struck with a trowel. The point of outlet of the main drain should be first fixed by studying the fall of the ground.

For large areas, such as public gardens, the services of a sur­veyor should be sought to obtain a series of levels. The water-level is a handy instrument for small schemes and is sufficiently accurate. It may be made from a piece of half-inch water piping, about two feet long, with an elbow at each end. Into each elbow, cement a piece of glass tubing about six inches long. A spiked rod attached to the centre completes the implement. When in use, fill the tube with coloured liquid and set in position. The fall of the drainage trench will be indicated by the difference in levels of fluid in the two tubes.

Before digging a drainage trench it should be marked out with a line to keep it straight. Commence digging at the lower end so that any water accumulating in the trench will run away and not mount up, causing inconvenience. The trench should be just wide enough to be easy to work in, about one foot. The depth is governed by the level of the clay or other impervious matter. The average depth is two or three feet, but it should not be less than eighteen inches. The topsoil should be placed on one side and the small amount of subsoil on the other. The latter should be discarded, its place being taken by the pipes and the cinders which are used to cover them. Should clay be put back in the trench it would render the drain less efficient.

In gaining levels the use of all instruments can be dispensed with by simply digging the trench by judgment, testing with water, and adjusting by results. The high spots are carefully levelled until the water does not lie anywhere, but slowly flows away. An occasional short, deep dip may be found in the clay. It should be filled in with pure clay rather than permit it to contain some less dense material that may allow the pipes to sink.

Though seldom necessary, a semicircular trough, two or three inches deep, can be cut in the bottom of the trench. If used, it should be tested with water.

Place the pipes firmly end to end and give each third one a kick with the heel to keep them firmly together. No matter how closely they are placed together they will never be close enough to keep the water out. The ends are not always quite square, but by twisting a pipe it will often be made to fit its neighbour better. If a gap of more than one-eighth of an inch has to be left it is better to arrange for it to be on the bottom than on the top, where it would allow silt to enter the pipe. The pipe at the highest level of the trench should be blocked with a brick. The outlet should be into a mass of cinders or be covered with fine wire-netting to keep out mice and other pests, which might eventually block the pipe.