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



Field Drainage systems

Field drainage systems are differentiated insurfaceandsubsurfacefield drainage systems.Sometimes temporary drainage is required whereby the drainage system is allowed to function on certain occasions only such as, during the harvest period. If allowed to function continuously, excessive quantities of water would be lost. Such a system is therefore called achecked, or controlled, drainage system. More usually, however, the drainage system is meant to function as regularly as possible to prevent undue waterlogging at any time and one employs aregular drainage system. This is sometimes also called a "relief drainage system".

 

Sometimes, a subsurface drainage system is installed in soils with a low infiltration capacity, where a surface drainage problem may improve the soil structure and the infiltration capacity so greatly that a surface drainage system is no longer required.

On the other hand, it can also happen that a surface drainage system diminishes the recharge of the groundwater to such an extent that the subsurface drainage problem is considerably reduced or even eliminated.

 

Usually, pipe drains or ditches are preferable to wells. However, when the soil consists of a poorly permeable top layer several metres 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.

 

When the land needs a subsurface drainage system, but saline groundwater is present at great depth, it is better to employ a shallow, closely spaced system of pipes or ditches instead of a deep, widely spaced system. The reason is that the deeper systems produce a more salty effluent than the shallow systems. Environmental criteria may then prohibit the use of the deeper systems.

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