Subsurface Drainage Contribution to Streamflow in the Corn Belt Region

Subsurface drainage is used to increase agricultural productivity in large parts of the US Corn Belt, by removing excess water from the root zone and allowing timely field operations. Drainage system play an important role for agricultural development in the region, however, nutrient rich runoff has resulted in elevated levels of nitrate in water resources of the US over the years, as well as alterations to regional hydrology. Analysis of the impacts of subsurface drainage is complicated due to by a lack of information on drainage extent. Subsurface drainage extent for the US Corn Belt is estimated based on land surface slope, land use and soil drainage class at 5 minute resolution, and evaluated at the county level using data from the 2012 Census of Agriculture. Calculation of the contribution of tile drainage to total runoff can be important in decision making. Information about hydrologic unit runoff from sub-watersheds from the USGS are used to calculate the fractional contribution of subsurface drainage to streamflow in the Corn Belt region which will be helpful to identify the regional influence on streamflow and water quality.