Creating A Scaling Relationship Between Peak Discharge And Drainage Area To Identify Tile Drainage Inputs Into An Agricultural Stream

Tile drains have been shown to contribute to high levels of nitrate in agricultural streams. Locations of tile drains on a watershed scale, however, are often unknown due to tile drains being located on many separate parcels of private property. This study evaluates the ability of a methodology, using scaling relationships between discharge and drainage area, for locating areas of large tile drainage contribution to Money Creek, in McLean County, Illinois. Additionally, this study examines the difference in scaling relationships and physical stream hydrology between tileflow and no-tileflow conditions. Eight stream sites were created in the watershed, that recorded stage every 15 minutes. The drainage area of each stream site was calculated in ArcGIS. Hydrographs were created from rating curves that were developed for each site, and used to create scaling relationships between peak discharge and drainage area for 21 storms throughout the study period. Overall, this method was not effective for detecting tile drain input into Money Creek, because there were no major differences in the outliers of the scaling relationships between the tileflow and no-tileflow periods. The scaling exponent means between the tileflow and no-tileflow period were statistically different. This is likely due to, factors that other studies have shown to cause regional differences in scaling exponents (evapotranspiration, soil moisture storage, and sunshine) are causing seasonal differences in the scaling exponent within the Money Creek watershed. Additionally, this study observed double peaks in storm hydrographs, which were interpreted as being caused from the difference in runoff generation timing between overland flow and tile drainage