Drainage system (agriculture)

The regular surface drainage systems, which start functioning as soon as there is an excess of rainfall or irrigation applied, operate entirely by gravity.

They consist of reshaped or reformed land surfaces and can be divided into: The bedded and graded systems may have ridges and furrows.

Checked surface drainage systems are also found in terraced lands used for rice.

[3] In literature, not much information can be found on the relations between the various regular surface field drainage systems, the reduction in the degree of waterlogging, and the agricultural or environmental effects.

It is therefore difficult to develop sound agricultural criteria for the regular surface field drainage systems.

[4] Similarly, agricultural criteria for checked surface drainage systems are not very well known.

[6] The subsurface field drainage systems consist of horizontal or slightly sloping channels made in the soil; they can be open ditches, trenches, filled with brushwood and a soil cap, filled with stones and a soil cap, buried pipe drains, tile drains, or mole drains, but they can also consist of a series of wells.

The field drains (or laterals) discharge their water into the collector or main system either by gravity or by pumping.

Disposal drains are main drains in which the depth of the water level below the soil surface is not bound to a minimum, and the water level may even be above the soil surface, provided that embankments are made to prevent inundation.

[7] The final point of a main drainage system is the gravity outlet structure [8] or the pumping station.

[9] Surface drainage systems are usually applied in relatively flat lands that have soils with a low or medium infiltration capacity, or in lands with high-intensity rainfalls that exceed the normal infiltration capacity, so that frequent waterlogging occurs on the soil surface.

However, when the soil consists of a poorly permeable top layer several meters thick, overlying a rapidly permeable and deep subsoil, wells may be a better option, because the drain spacing required for pipes or ditches would be considerably smaller than the spacing for wells.