In the North Central Region, the eight states that make up the Great Lakes and Cornbelt states (Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio and Wisconsin) are some of the most highly drained states in the nation. The table at right shows the status of drainage in 1985 within these eight states and their rank among all states in the approximate area of land drained (including surface and subsurface drainage and irrigated areas with special drainage needs). The percent of all cropland drained within a state provides an indication of dependence on drainage. In both Indiana and Ohio, at least 50% of all cropland has drainage improvement.
Historically, estimates of drainage development in the United States have been made by the USDA from Bureau of Census information and supplemented with data available from USDA agencies and university and industry drainage specialists. Drainage in the United States occurred in two primary developmental periods, during 1870-1920 and during 1945-1960. Early settlers in America employed European drainage methods, such as small open ditches to drain wet spots in fields and cleaning out small streams. American farmers increasingly found that large outlets beyond individual farm boundaries were necessary to provide proper farm drainage. The construction of such outlets has been facilitated greatly by the establishment of drainage districts, county drains, or other drainage enterprises organized under state laws.
Around 1830, increased public pressure was brought on Congress to release federal swamp and wetlands for private development. After 20 years of deliberation, Congress passed the Swamp Land Acts of 1849 and 1850. These were the first important pieces of Federal legislation relating to land drainage. Little progress in land sales occurred until state laws permitted organization of drainage and levee districts, and the organization of drainage projects by county governments with the consent of the majority of beneficiaries. By 1920, more than 53 million acres out of a total of 956 million acres of U.S. farmland had received some form of drainage. By 1960, 86.6 million acres of non-federal, rural land had been drained. This figure rose to 109.7 million acres by 1985. Of this total, 75.5 million acres (69 percent) was used for cropland.
In a 1982 survey completed by the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service), non-Federal rural land in the United States having wet soils (not necessarily wetlands) totaled over 233 million acres. Of this total, 45 percent was cropped and 30 percent forested. The 1982 inventory identified about 107 million acres of the wet soils as being prime or adequately drained, of which 72 percent was then cropland. Unfortunately, no comprehensive surveys of agricultural drainage have been conducted since 1982.
Several factors make drainage a necessity for agricultural production on some land. These factors include slow soil permeability, flat or depressional topography, restrictive geologic layers underlying the soil profile, and periods of excess precipitation. Texture affects permeability, or the ability of soils to drain water. Slowly permeable soils contain relatively large percentages of clay- and silt-sized particles which hold water well but do not drain well. Coarse soils contain a large percentage of sand-sized particles, and tend to hold less water but drain well. The permeability of the soil is affected by soil structure as well. A granular soil structure promotes the movement of water through soil while a massive structure with little or no granular components decreases the movement of water. Compaction on agricultural land from the use of production equipment on wet soils destroys soil structure and creates a layer that restricts the downward movement of water.
Soils that hold water well tend to be saturated and wet in the spring and fall when farmers need to plant and harvest their crops. When soils are saturated, excess precipitation is more likely to either pond on the soil surface or become runoff.
Percent of all cropland that is drained within each state. The figures,
revised for 1998 are based on expert opinion. No comprehensive survey
has been conducted since a 1985 USDA effort (results shown in table at
right). Discrepancies highlight the need for a new survey to quantify
changes in drainage development over the last 15 years, and to make
projections for the future.
Timeline showing primary periods of drainage development in the United
States. Drainage development rates stabilized during the depression and
war years (1920 to 1945) and again after 1960.
|Drainage statistics for highly-drained states in the North Central|
Region of the United States. Taken directly from "Farm drainage in the United
States: history, status and prospects" by the USDA (Misc. Pub. No. 1455.
Washington, D.C., 1987).
There are two main reasons agricultural drainage systems are installed in the Midwestern and Great Lakes states: (1) to allow timely seedbed preparation, planting, harvesting, and other field operations; and (2) to protect field crops from extended periods of flooded soil conditions.
Percent of all land (agricultural and non-agricultural) that is drained
in each North Central state (1985 USDA data).