Identifying deep-groundwater discharge in rivers of eastern Ontario

Interactions between surface water systems and groundwater systems are poorly understood. This research focuses on the surface water/groundwater interactions that use an electric conductivity and temperature (EC&T) drag probe in the Raisin River and South Nation Watershed.;To find groundwater seepages into rivers, a Reelogger Model 2001 probe (Solinst Canada Ltd) was dragged at the sediment-water interface to measure EC&T for several reaches of the Raisin River, the Castor River, the East Castor and the South Nation River. GPS position data was collected at the same time as the EC&T measurements which allows the data to be input into a GIS database for management decisions. During the summer, groundwater typically had higher EC and lower T values than the surface water, and so increases in EC occurring along with lower water temperatures were inferred to be deep-groundwater discharge locations. High EC values can be explained either by deep groundwater discharge (seeps) or by local anthropogenic loading of sediments into the river. In rivers with low permeability clay streambeds very few locations of significant discharge were detected using this method. The most significant discharge area, called the "Swimming Hole" by local residents, was surveyed at large and small scale and groundwater seepage was found to be present along the shore and in the middle. However, the EC&T probe appears to have identified relatively high flux discharge zones in the Castor and East Castor River at locations where highly permeable eskers cross the rivers. The survey identified approximately a 50 m area along the Castor river and a 100m area along the East Castor River where EC values were as high as 2000 muS/cm and temperature as low as 11°C. They were investigated and fluxes quantified by installing and testing piezometers and deploying seepage meters.