Agricultural Drainage Tiles: An Overview of their Use, Benefits, and effect on Hydrology and Water Quality

Agricultural drainage tiles (ADTs) have become an integral part of the Midwest’s economy by their ability to transform fine-grained, poorly drained soils into highly productive farmland. Because of their design and function, they also pose a number of detrimental consequences related to water quality, stream bank erosion, a loss of wetland areas, increased baseflows, and flooding intensity. This research paper explores how ADTs contribute to the agricultural pollutant loading problem experienced in Midwest streams. It also identifies new practices and technologies being pursued to mitigate their impact. ADTs provide unique field-to-water pathways for a number of agricultural pollutants, the most critical of which are nutrients. Since ADTs bypass traditional conservation practices used to mitigate the environmental impact of row crop agriculture, contaminants often reach streams with very little, if any, attenuation. ADTs also represent a major alteration in the Midwest’s hydrology as they greatly enhance the connectivity between fields and streams. As a result, natural storage areas that once occupied the landscape and gradually released water to streams have been lost, water tables have been lowered, and baseflows have increased. Because of their profound effect on contaminant transport and hydrology, it’s now realized that ADTs play a significant role in nutrient loading of Midwest streams and rivers. To mitigate the negative effect of ADTs on water quality, a strategic combination of targeted management practices and new technologies is needed. These include traditional soil conservation practices, new regulations, constructed wetlands, bioreactors, controlled drainage management, and re-routing tile drainage as sub-surface flow across riparian buffers