What is Drainage?
[[Image:Zuider1.jpeg|thumb|right|250px|The Zuiderzee in the [[Netherlands]] was partly changed into land by building [[polder]]s and draining them. Old land is mostly green, new one is darker in color.]] '''Drainage''' is the natural or artificial removal of surface and [[groundwater|sub-surface water]] from a given area. Many [[Agriculture|agricultural]] [[soil]]s need drainage to improve production or to manage water supplies. ==Early history== The earliest archaeological record of an advanced system of drainage comes from the [[Indus Valley Civilization]] from around [[3100 BC]] in what is now [[Pakistan]] and North [[India]]. The ancient Indus systems of [[sewer]]age and drainage that were developed and used in cities throughout the civilization were far more advanced than any found in contemporary urban sites in the [[Middle East]] and even more efficient than those in some areas of modern Pakistan and India today. All houses in the major cities of [[Harappa]] and [[Mohenjo-daro]] had access to [[water]] and drainage facilities. Waste water was directed to covered drains, which lined the major streets. == Reasons for artificial drainage == [[Image:Oude Haarlemmermeer.jpg|thumb|250px|Historic map of the Haarlemmermeer prior to reclamation.]] [[Wetland]] soils may need drainage to be used for [[agriculture]]. In the northern [[United States|USA]] and [[Europe]], [[glaciation]] created numerous small [[lake]]s which gradually filled with [[humus]] to make [[marsh]]es. Some of these were drained using open [[ditch]]es and trenches. The largest project of this type in the world has been in process for centuries in the [[Netherlands]]. The area between [[Amsterdam]], [[Haarlem]] and [[Leiden]] was, in [[prehistoric]] times swampland and small lakes. Turf cutting ([[Peat]] [[mining]]), [[subsidence]] and shoreline [[erosion]] gradually caused the formation of one large lake, the [[Haarlemmermeer]], or lake of Haarlem. The invention of [[wind]] powered [[pump]]ing engines in the [[15th century]] permitted dra