ASSESSING THE IMPACT OF SUBSURFACE GEOLOGY ON GROUNDWATER DYNAMICS AND TILE DRAINAGE FUNCTION

Artificial drainage relies on manipulating the water table to remove excess water and allow for longer, more productive growing seasons. 14% of Canada’s cropland and 27% of agricultural land in the United States are drained artificially. These numbers are likely to increase as farmers are forced to adapt to changes in the frequency and magnitude of severe weather events due to climate change.

Understanding the structure and composition of the subsurface and its groundwater flow system is essential for effective tile drainage. Hydrogeologic assessments are rarely undertaken during tile installation, resulting in poor understanding of tile drain-groundwater interactions.

Huronview Demonstration Farm (HDF) in Clinton, Ontario, Canada is used to test various kinds of tile drainage systems to improve the sustainability of agricultural production. The HDF offers an opportunity to address the research gap on a working farm – identifying relationships between the Quaternary sediments that form the subsurface on site, hydrogeological units, and the efficiency of tile drain configurations (patterned, contoured, untiled), while also identifying the impact tile drains may have on groundwater.

Five monitoring wells and three downhole geophysics access tubes were installed in continuously cored boreholes at the HDF (total core recovered: 86.32 m). Natural Gamma and Conductivity profiles were conducted in all monitoring wells, and Electrical Resistivity Tomography was conducted across the study site. The deepest borehole extends 30 meters below ground surface. From the surface downward, cores comprise multiple diamict units, coarse sand, saturated very fine sand, laminated clay with drop stones, and massive, uniform clay. Data collected from core and downhole geophysics support lateral sediment heterogeneity across the HDF, which may explain the varying performance of tile drain function. A conceptual site model is presented to characterize the subsurface and aid in understanding how the groundwater and tile drains connect.