Subsurface field drainage

Due to its high cost, subsurface drainage, generally by perforated tube or tiles, is rarely employed in South Asian irrigation in view of its high cost, although there are large areas which offer no other alternative if full reclamation or development is to be achieved. The problem of the close spacing required for drainage of low permeability clay soils has been referred to earlier. Special situations do occur in which the presence of an underlying horizon of more permeable material permits much wider spacing of pipe drains, in conjunction with vertical chimney drains extending down to the latter horizon. However, these situations are the exception. All other expedients should be explored before tube drainage is seriously considered, the expedients including lowering the watertable by restricting irrigation supply, by lining of irrigation canals, by groundwater development, or by changing land use to unirrigated tree plantations or to pond fishculture.