Mapping Subsurface Drainage Systems using Remote Sensing and GIS

Subsurface drainage is a widely used water management practice in many areas of the Midwest. In flat, poorly drained soils, growers must rely on subsurface drainage as a practical and economical solution to remove excess water from cropland. Subsurface drainage systems have been installed for over 100 years, many of which are still operational. Traditional methods for locating tile systems are time consuming and labor intensive. This paper outlines the development of a method for locating and delineating existing tile systems using remote sensing and GIS technologies. Tiles are located using color infrared aerial photographs. Because the soil directly above a tile line dries faster than the surrounding soil, the reflectivity of the drier soil is often clearly seen in the infrared spectrum. Tile lines are delineated within a GIS framework by overlaying aerial imagery with soils and elevation maps. To illustrate this method, tile systems are delineated from a 640-acre section of tile drained cropland and then expanded to a 17,500-acre tile drained watershed in East Central Illinois.