DRAINAGE. 430 DRAINAGE. Nenc and the Old R'dford river:-) tlmt an irrup- tion look place in 1802, whicii strikingly illus- trates the dcjwndenee of the safety of the whole region on well-formed and well-maintained embankments. There wa.s a sluire, called Saint Germain's sluice, situated at the conlluence of the Mid- dle Level main outfall drain with the Kiver Uuse, near the upper end of another arti- ficial channel, known as the Eau Brink cut. On May 4, 18ti"i, this sluice gave way without the slightest warning; the tidal waters under- mined the brickwork, and formed a hole in the bed of the river, into which the works of the sluice sank. The tidal waters rushed up the opening, and ebtjed and (lowed throughout a dis- tance of 20 miles. An attempt was made to throw an earth and cradle dam across the drain, at about 500 yards from the fallen sluice; but this was relin(|uished in favor of a permanent cotVordam of pile-work, at a distance of half a mile from the sluice; and after incessant exer- tions from -May Hi to .func 111, the tidal waters were at length effectually shut out by a strong dam. The failure of the Saint Germain's sluice was not the only irruption that had to be battled with ; eight days after that failure, under the pressure of a high spring-tide, the west bank of the drain gave way, on May 12, at a point about four miles from the sluice; the bank had been built only to resist upland waters and not a rush and a pressure of the sea. The rupture carried away 70 yards of the bank, scouring out a hole 10 feet deep at the spot, and admitting a rush of water which covered (iOOO acres of fertile land to a depth of two or three feet, increased at successive high tides to 10.000 acres. in completing the re[)a'irs, it was decided to substitute syphons for sluices to carry oil" the water, but these, after being operated a number of years, have been abandoned in favor of a new sluiceway. The attempt to carry ofT the water from the fen-lands by gravity has in no instance proved completely successful. Pumping plants have therefore been installed here and there, to carry olT the water, either constantlv, or at Hood seasons. In the valley of the Po, iiOO.OOO acres of marsh- land have been drained and transformed into rich farm-land, the water being lifted off by pumps. The same kind of work has been done in the south of France. In America, a large amount of land-reclama- tion work, by gravity-canal systems, has been a(Coni[)lislied in Florida. Illinois, Indiana, and Minnesota. Two drainage canals have been con- structed in the Red Uiver Valley of Minnesota, which have reclaimed 2.'J0,000 acres of land. One of these, which is 7 miles long. 20 feet wide at the bottom, and which varies at depth from 3 to 10 feet, was constructed at a cost of about 11 cents a cubic yard of excavation. In Florida, the work of draining marsh-lands lias l)een intrusted to various private com- panies under land grants or pnrcliases. Some of the companies have construcli"! only the main drainage canals, le;iviiig the subsidiary canals and ditches to be dug by purcha.sers. Other companies have not only developed but also cultivated the land, transforming it in some casj's into sugar phiiitatinns. Florida, with its fertile soil and subtropical climate, offers a wide field for land reclamation, for it is esti- mated that, out of a total area of .')8,700 square miles, 4400 square miles are water surface, and 14,000 more are swamp lands. The swamp lands are of dilferent kinds. There are (1) those bordering rivers and subject to the rise and fall of the latter, which in most cases can only be drained by constructing embankments and pumping; (2) large mbra.sscs near the sources of rivers, which, being at the head- waters of the streams, can be drained by gravity; (3) large shallow ponds, which, when drained or in dry seasons, become fertile prairies. Thus far the work done has chielly consisted in dig- ging shallow gravity canals, and in widening ami deepening existing chanels. Within the limits of the city of Philadelphia, Pa., several thousand acres of cultivated land lie below the tide levels of the Delaware and Schuylkill rivers, protected from inundation by at least 200 miles of surounding dikes and drained by numerous canals and ditches. Various schemes have been proposed from time to time for draining the Newark and llackensack meadows, but at the close of the nineteenth century nothing effectual had been accomplished. These salt marshes or meadows, embracing an area about IS miles long and 4 miles wide, and surrounded by some of the most thickly populated districts in the world, are sorely needed by the overflowing j)opula- tions of New York, Jer.sey City, and Newark. They are crossed by twelve important lines of railway and intercei>ted by a navigable river. They are covered with a luxuriant crop of sedge- grass, which forms a breeding-place for mosqui- toes and other pests. Consult Wheeler. The Drainage of Fens and Lowlands by flraiitalion and Steam I'oirrr (London, 1888). For drain- age and sewerage of cities, see Sewerage. Drainage of Farm-Lands. The earliest method of freeing land from superfluous water was by open ditches and drains, but throw- ing up the land in beds, hilling, and ridging N'o. 1, IniiK-haiKllcil shoTel for loose earth ; 2, 3, 4, lipiulM tor illKKlnK till' ditch. w<'re practiced with the same object in view. These, however, arc only partial and super- ficial in their effects. The Roman agricul- tural writers mention the good results arising
