Drained areas are former wetlands and artificial wetlands are often placed in formerly drained areas. Similar microbial processes, mass balance principles, and energy-flow relationships can be used to assess both drainage and wetlands designs. Hydrological cycle and drainage Drainage is the removal of excess water from the soil.
Water is added by rainfall, irrigation or subsurface groundwater to the crop root zone.
If a high water table or subsurface impermeable layer restricts the downward movement of soil water, then soil waterlogging reduces crop production. In irrigated regions, high water tables lead to salinization of soils. Large natural wetland areas of the Midwest and Southern United States were drained and farmed. Before excessive aquifer pumping in Tucson, the rivers contained water year round and provided a sanctuary for birds and other wildlife, such as mosquitoes with malaria. When wetlands are eliminated by drainage, animal and bird habitats are eliminated so certain species of migratory birds and local wildlife are endangered.