Guidelines and computer programs for the planning and design of land drainage systems

FAO Irrigation and Drainage Paper 62

by W.H. van der Molen
Wageningen University
Wageningen, Netherlands

J. Martínez Beltrán
Water Development and Management Unit
FAO Land and Water Division

W.J. Ochs
Water Management Engineers
Annandale, United States of America

Drainage of agricultural land is one of the most critical water management tools for the sustainability of productive cropping systems, as frequently this sustainability is extremely dependent on the control of waterlogging and soil salinization in the rootzone of most crops. On some agricultural lands, the natural drainage is sufficient to maintain high productivity. However, many others require improvements in surface and subsurface drainage in order to optimize land productivity, while maintaining the quality of soil resources. As time passes, drainage requirements may change because of changes in the general socio-economic conditions, such as input and output prices, and more intensive crop rotations.

In rainfed and irrigated areas of the temperate zones (where waterlogging is the dominant problem in lands lacking natural drainage), proper drainage has improved soil aeration and land and rural road trafficability. Moreover, it has facilitated the lengthening of the potential crop growth period.

In the irrigated lands of the arid and semi-arid regions (where salinity problems dominate), in addition to the benefits described above, subsurface drainage has been essential for controlling soil salinity and reducing the incidence of erratic crop yields. In the semi-humid and humid tropical regions, drainage development has been less than in the agroclimate zones mentioned above. However, salinity control is required during the irrigation season in the semi-humid tropics, as is waterlogging control during the rainfall season (e.g. in countries with monsoon rainfall). In addition, flood control is also often a necessary component of drainage projects in many of these areas in order to protect the safety and livelihood of the rural population more effectively. In plains in the humid tropics, occurrences of organic soils or acid-sulphate soils often present special problems whose resolution entails careful drainage.

The general goal in all agroclimate zones is to obtain a proper water table control necessary at the given time and under the given circumstances. Sometimes, special water control methods are required, e.g. in acid-sulphate soils and in peat soils, and in areas where rice is grown in rotation with dry-foot crops.

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