Installation Depth of Subsurface Drains in Arid and Semi-Arid Regions; Challenges and Solutions

The main challenge in determining drainage depth in arid and semi-arid regions is the inefficiency of shallow drainage in salinity control and producing more drainage water by deep drains which is also more saline and more polluted. In the irrigation season, the focus of drainage is mainly on soil aeration, and the depth of the drainage design should keep the groundwater level in a position that avoids damages caused by waterlogging. During the non-irrigation period, the minimum depth required for drainage should be such as to prevent salinity increase through the capillary flow. Controlled drainage is the best way to overcome the conflict of salinity control and less damage to the environment. However, necessary equipment and structures for these systems are costly, as well as operational and maintenance problems, have led to a lack of expansion of such systems in developing countries. The simplest and cheapest solution to the problem is to plow the soil or any other tillage operation that will cut off the capillaries. But post-harvest plowing exposes soil organic matter to sunlight that is rapidly oxidized, which will have a negative impact on soil fertility. Another suggested solution is a bi-level drainage system. In such a system, the task of controlling the water level in the irrigation season is mostly the responsibility of shallow drains. In the non-irrigation season, the water level drops to deeper drain levels and the potential for re-salinization by capillary up-flow will be reduced.