Effect of subsurface drainage on streamflow in an agricultural headwater watershed

•The influence of subsurface drainage on watershed hydrology was investigated.•Tile drainage accounted for 47% of watershed discharge and was seasonally variable.•Results show that tile drainage has a significant impact on watershed hydrology.•Quantifying tile discharge at this scale is critical for determining nutrient losses. Artificial drainage, also known as subsurface or tile drainage is paramount to sustaining crop production agriculture in the poorly-drained, humid regions of the world. Hydrologic assessments of individual plots and fields with tile drainage are becoming common; however, a major void exists in our understanding of the contribution of systematic tile drainage to watershed hydrology. A headwater watershed (4km2) in central Ohio, USA and all functioning tile were monitored from 2005 to 2010 in order to characterize the magnitude and frequency of flows, quantify the role and seasonal contributions of tile drainage to watershed hydrology, and relate tile drainage to precipitation and antecedent conditions. Results indicated that tile drainage contributions to watershed hydrology were significant. Specifically, 21% of precipitation (206mm) was recovered through tile drainage annually. Tile drainage also accounted for 47% of watershed discharge and was seasonally variable. Median monthly tile discharges in winter (23.4mm), spring (10.2mm), and fall (15.6mm) were significantly greater (P