Drainage

Drainage, removal of surplus water from land. Withot drainage, successful crop production and retention of soil fertility would be impossible. Wet lands are difficult to work with modern machinery, and most crops suffer from root injury if grown on water-logged ground. Undrained soils are structureless, with tightly packed subsoils full of stagnant water. Buildings and houses benefit from drainage, which is essential for sanitation and good health. Roads are not passable in wet weather unless provided with drains. Undrained swamps afford breeding grounds for malaria-carrying mosquitoes, and accumulated sewage becomes a source of disease epidemics. Early drainage consisted mainly of open ditches, often using natural watercourses. During the 18th century farmers began to employ patterns of underground channels covering whole fields, which collected and discharged surplus water into several outfalls. The invention and mass production of U-shaped clay or concrete drain tiles in England in the mid-19th century opened the way for the wide adoption of tile draining. On clay land, mole draining is effective: A mole plow moves over the surface of the ground, drawing a cylindrical mole through the subsoil, making a channel about 3–4 in (7.5–10 cm) wide, some 2 ft (60 cm) below the surface. This method, with the variations, comes under the heading of surface drainage. Excess water can also be pumped off land.