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Extensive agricultural subsurface "tile" drainage in the Midwestern U.S. has important implications for nutrient pollution in surface water, notably the seasonal hypoxic "dead zone" in the Gulf of Mexico.

However, drainage data limitations have constrained efforts to effectively factor tile drainage into regional economic and environmental impact studies.

Better drainage data would be a valuable addition to future modeling applications.

In light of this need, a methodology incorporating a geographic information system (GIS) analysis based on soil and land cover maps was used in addition to existing data to create a set of county-level tile drainage extent estimates.

These estimates are downloadable for review in order to evaluate existing data and the results of this GIS analysis, with the goal of arriving at an improved picture of tile drainage in the U.S.