Well drainage is the removal of water from agricultural and other lands with the use of underground wells. Known as dry or shallow injection wells, they provide a route for water to exit land under cultivation to control conditions in the soil. There are some environmental concerns with this practice which have led governments in some areas to encourage farmers to use alternate means of water control, and to close existing wells. Such programs sometimes provide financial assistance to help land owners close and seal old agricultural installations.
One service provided by well drainage is better control of the water table, particularly in reclaimed wetland and lowland areas. Without proper drainage, soil can become boggy and marshy, which can damage crops. The water table may rise very high in the rainy season, and can create problems for the farmer. A series of drainage wells, carefully spaced through the fields, can keep it at a stable level. Soil in the growth zone may be moist, which can facilitate growth, but should not be waterlogged, which can kill seeds and plants.
Controlling levels of saline and other compounds in the soil can also be a concern. Well drainage may help farmers with soil chemistry problems. The positioning and spacing of the wells is critical, as they need to be located in the optimal locations for the given crop and conditions. Soil scientists and other consultants may offer advice on the best location and spacing. Permit applications are often required for well drilling, which gives government agencies a chance to review plans and identify concerns before the wells are sunk.
Installation costs can depend on the number of wells and any accessory drainage system installed at the same time. Farmers may weigh the cost of well drainage against other options, and the cost of doing nothing. Reclamation of farmlands with high water tables can also require ongoing maintenance efforts to keep the water under control, and thus may lead to the need for more profitable crops to support the associated expense.
The primary environmental concern with well drainage is the risk of contamination. Agricultural runoff can contain fertilizers, herbicides, pesticides, and other chemicals that may damage the natural environment. Poorly controlled agricultural well drainage may pollute the groundwater, which can limit supplies of safe drinking water in addition to threatening the environment. Older wells can be closed to limit these risks, and there are alternatives to well drainage available to help farmers manage soil chemistry and water levels more safely.