This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities. Agenda 21 recommends introducing surface drainage in rain-fed agriculture to prevent temporary waterlogging and flooding of lowlands.
Drain tiling involves installing a network of subsurface drainage tubes 2 to 4 feet below ground to siphon off excess water. Groundwater flows through the pipes rather than the soil, because the pipes offer a pathway of least resistance. As a result, the groundwater table is lowered to the depth of the pipes thus ensuring that a crop’s roots won’t become water logged, and that fields drain earlier in the spring. The pipes are usually oriented to discharge into a nearby stream, though in some cases, the discharge may just be to an area lower in elevation.
While surface drains and drain tiling may be an attractive option, allowing farmers to grow crops on less than ideal land, the practice has serious ramifications for the environment as it dramatically increases the speed at which nutrient runoff enters rivers and streams. Since the water is shuttled out through surface channels or underground pipes, rainwater is no longer being filtered through soil into aquifers.