Driving through rural Minnesota, Iowa, Illinois, and Indiana, it appears that buildings are scarce. It seems that people built their landscape entirely from crop plants and a few trees protecting their homesteads. But look closer where the soil is bare in spring and you may be able to see the light lines of drier soil running across the fields, hinting at the vast construction project that has been under way for the last century. Under nearly every acre of Midwestern cropland lies a network of cylindrical tiles - originally clay and now plastic - that draws water out of fields and into drainage ditches, streams, and ponds. Without these, agriculture would not be possible in vast expanses of the Midwest that were dominated by "prairie potholes" - low spots a few acres in size where the water table is near or above the soil surface for much of the year.
Drainage technology was first used in the United States in the mid-1800's for public health purposes. New York City's Central Park was drained in 1858 to reduce the habitat for mosquitoes and other disease vectors. A second purpose of drainage is to remove salts from irrigated land in arid regions. Drainage allows the leaching of salts from the root zone. In the Midwest and other humid areas, the purpose of drainage is to remove excess water and lower the water table. This creates a well-aerated environment for roots and soil organisms. Drainage allows earlier warming of soil in the spring, and earlier traffic on fields. Installation of drainage tiles can have a rapid and large return on the capital investment, by substantially improving productivity.
Drainage has been part of U.S. agriculture since colonial times, but it expanded to a broad scale when Europeans settled the Midwest. At the time of settlement, large proportions of Illinois, Ohio, Indiana, Minnesota, Iowa, and Missouri were swampland unsuited to normal cultivation. Large areas in northeastern Arkansas, the gulf plains of Texas, and delta areas of Mississippi and Louisiana were also originally swamp and overflow areas. Most of the drainage of the Midwestern wetlands occurred in the early 1900's in response to federal and local government support for drainage districts and improvements in drainage technology. Despite the Depression, the federal government provided financial assistance in the 1920's and 1930's to maintain and expand drainage systems. Drainage of arid, irrigated lands in the west expanded at the same time. Drainage systems generally require organization among land owners in a drainage district to coordinate outlets. Beginning in the 1970's and 1980's the federal government discouraged further draining of wetlands.
Drainage changes the hydrology of the soil system to such an extent that drained land may no longer be considered the same kind of soil. Drainage may reduce erosion by reducing overland flow of water, but it also speeds the transport of water and soluble chemicals and nutrients through the soil, into drainage tile lines, to be discharged to surface water. One of the obvious effects of drainage is the loss of wetlands and their benefits including wildlife habitat, water recharge and discharge, flood storage and desynchronization, shoreline anchoring and dissipation of erosive forces, sediment and contaminant trapping, nutrient retention and removal, and recreation.
When peatlands and other high-organic matter soils are drained, they rapidly subside as the organic matter is decomposed by organisms responding to the newly available air.
To learn more about the history and technology of soil drainage, see:
Farm drainage in the United States: history, status, and prospects. 1987. George A. Pavelis. Washington, D.C.: U.S. Dept. of Agriculture, Economic Research Service, Series: Miscellaneous publication (United States. Dept. of Agriculture); no. 1455.
For data about the extent and economic value of drainage systems, see:
Natural resource capital formation in American agriculture: irrigation, drainage, and conservation, 1855-1980. 1985. George A. Pavelis. Washington, D.C.: U.S. Dept. of Agriculture, Economic Research Service, Natural Resource Economics Division.