International Commission on Irrigation & Drainage Commission Interationale des Irrigation et du Drainage

Surface Drainage Systems

Surface drainage is the diversion or orderly removal of excess water from the surface of land by means of improved natural channels or constructed drains, supplemented when necessary by shaping and grading of land surface to such drains.


Improvements are designed for two purposes: to minimize crop damage resulting from water ponding on the soil surface following a rainfall event, particularly in ground slopes less than 2%, and to control runoff without causing erosion for steeper land slopes. 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.


This type of improvement includes: land levelling and smoothing; the construction of surface water inlets to subsurface drains; and the construction of shallow ditches and grass waterways, which empty into open ditches and streams.


Surface drainage systems can be classified into Regular Surface Drainage System and Controlled Surface Drainage System.The regular surface drainage systems, which start functioning as soon as there is an excess of rainfall or irrigation, operate entirely by gravity. They consist of reshaped or reformed land surfaces and can be divided into bedded systems, used in flat lands and graded systems, used in sloping lands.The bedded and graded systems may have ridges and furrows.


The checked or controlled surface drainage systems consist of check gates placed in the embankments surrounding flat basins, such as those used for rice fields in flat lands. These fields are usually submerged and only need to be drained on certain occasions (e.g. at harvest time). Checked surface drainage systems are also found in terraced lands used for rice.


Surface drainage can affect the water table by reducing the volume of water entering the soil profile. Surface drainage improvements require annual maintenance and must be carefully designed to ensure that erosion is controlled. At the same time extensive earthmoving activities are expensive, and land grading might expose less fertile and less productive subsoils. It reduces the agricultural area. Further, open ditches may interfere with moving farm equipment across a field.

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Dictionary - Surface Drainage Systems Terms

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