USDA LTAR Common Experiment measurement: Discharge from artificial subsurface drains v1

Subsurface drain discharge, sometimes simply referred to as drainage, is a process by which water is removed from a soil profile or area (ASABE, 2015). On agricultural lands with intermittent high-water tables due to precipitation or melting snow, water is removed using artificial (generally referred to as tile) drains or ditches to allow timely field operations and protect growing crops from being waterlogged. This discussion is limited to artificial subsurface (tile) drain discharge. In agricultural regions where crop production requires artificial subsurface drainage, drain discharge can represent a substantial portion of the annual water budget. Thus, measuring this water flow is important in understanding the water use of crops and potential impacts on downstream water movement. The measurement of subsurface drain discharge, together with a measurement of sediment and water pollutants, provides an assessment of the losses of these constituents from agriculture to the environment. Tracking them over time quantifies the beneficial effects of improved agricultural practices.