DRAINAGE. 431 DKAINAGE. from covered drains, which were formed of stone, wood, or other substances. Cato, who wrote in the second century u.c, gave specilic directions for drainage. The art of drainage was understood and practiced at a much earlier date by the Kgyptians and Babylonians. Primi- tive methods were also practiced to a limited extent in early days in Great Britain, and on the Continent of Europe. The progress of draining, however, was slow and partial until well on in the nineteenth century, when tlie prac- tice was reduced to a system. Practical men consider the line of greatest fall, or quickest descent, the best for cutting drains in a field. A fall of at least one inch in 100 feet should be secured, if possible. The most efficient system of drains can be laid out only after careful leveling (q.v. ) of the land to be drained. The smaller drains usually open into larger or main drains, which are laid in the lowest ground, instead of each dis- charging its quota of water into an open ditch. This is rendered necessary as the mouths of the smaller drains would be more liable to be choked up by the growth of weeds; while the collecting of water into main drains secures a fuller flow to sweep out any matter which might acounnilate where the f1 discharge is small. ^Moreover, the less the action of the air in the drains, the more efficient they are. Tlie most efficient and at the same time the cheapest drain is made so that a pipe of cylindrical form may be laid along the bottom, which need be of no greater width than is necessary to allow of the pipes be- ing properly laid. Drains of this form are cut with a set of spades, which are of different widths — the broader implements being used for taking out the top, and the narrower for the bot- tom. The implement which prepares the bottom of the drain for the tile is called a draining-scoop, of which there are a variety of forms. Va- rious forms of ma- chines adapted to dig- ging ditches for un- derground drains are 1. proovp-maker (ir round found in the market, tilp ..perat«-d by pushiiiK; 2 Before the general use and 4, the same for nf.xaK"»naI . . P tile; 3. s'""«^'^-niaki?r lor of pipes, stones were round tUe, operated by draw- the common mate- ^^- rials with which drains were formed. It was recommended that they should be broken so as to pass through a ring two inches and a half in diameter. From nine inches to a foot in depth was the quantity which was commonly put in. When tiles and pipes were nXISHINO TOOLS. first used, it was even thought necessary to have some gravel, or small stones, placed above them in the drains, for the purpose of enabling the water to find its way into them. It was soon found, however, that tile drains were quite as ellicient without any stones or gravel ; and that they were less liable to be choked up, as the clay or earth acted as a filter in preventing the in- trusion of any kind of solid matter. Many kinds of tiles and pipes have been tried, but the cylindrical form is most used. At one time a bore of one inch diameter in the tile was thought sufficient, bvit tiles of three to four inches are now preferred. They are usually made 12 or 15 inches in length. The con- tinuity of the drain is sometimes maintained by collars, but these are expensive and are not considered necessary. In soft or clayey sub- soil semi-cylindrical tiles have been laid with the bend up. but this is rarely, if ever, necessary. The size of the tile required depends on the size of the area to be drained. Waring gives the following directions for average conditions. With drains 4 feet or more in depth, laid on a uniform fall of 3 inches in 100 feet: For "2 acres, 11/4 -inch pipes: for 8 acres,"»2 14 -inch pipes: for 20 acres, 3l-o-inch pipes; for 40 acres, two 3%- inch pipes: for 50 acres, 6- inch pipes: for 100 acres, 8-inch pipes. Elliott gives the following tables, based on Kutter's formula, for determin- ing the number of acres a tile of given diameter and per cent, of giade will drain. They are applicable to main drains, well laid, where the water is supplied to them by sub-mains and laterals. Table 1 gives the discharge in cubic feet per second for sizes of tile-drains from 4 inches to 20 inches in diameter, computed on a grade of 1 per cent., or 1 foot per 100. Table 2 gives the square roots of grades from 0.04 foot per 100 feet to 1 foot per 100 feet: Table 1.— Discbarge of Tile from 4 to 20 Inches in Diameter o.n' a Grade of 1 Foot per 100 Feet Diameter Discharge in Diameter Discharge in ot tile cubic feet of tile cubic feet in inches per second in inches per second 4 0.16 10 2.05 5 .31 12 3.40 6 .49 15 6.29 7 .72 18 10.37 8 l.H 20 13.85 9 1.53 Table 2.- -Grades per 100 Feet, and Their Square Roots flrade Grade in inches (approsi- niatedj Square Grade Grade in Square per 100 ft. in feet root of grade per 100 ft. inJeet (approxi- mated) root of grade 0.04 i 0.200 0.35 4} 0.592 .03 i .224 .40 4 .632 .06 i .245 , .45 5 .671 .07 f .265 ! .50 6 .707 .08 .283 ; .55 6| .742 .09 1 .300 .60 7J .775 .10 H .316 .65 "^ .806 .12 H .346 .70 .S37 .14 .374 .75 9 .866 .15 .387 .80 98 .8S»4 .16 2 .400 .85 lOi .922 .18 n .424 .90 m .949 .20 .447 .95 .975 .25 . 3 ..WO 1.00 12 1.000 .30 31 .548 ! To determine the number of acres that a tile main of given size and grade will drain, mul- tipl}' the discharge of the tiles, according to size.
