QUANTIFYING VERTICAL STREAMBED HYDRAULIC CONDUCTIVITY USING 1D TEMPERATURE PROFILES AND HYDRAULIC GRADIENT MEASUREMENTS IN A GAINING STREAM REACH IN SOUTHERN ONTARIO

Groundwater discharge into streams is important because it affects surface water quality and quantity. However, a thorough understanding of groundwater flow patterns and associated geochemical mass flux is difficult because of the spatial and seasonal heterogeneity of flow through the streambed. This is particularly important in watersheds where non-point source contaminants such as nitrate and road salt are concerned, and where the downstream receptors include the sensitive ecosystems of large lakes. Hydraulic conductivity is a major factor for quantifying fluxes, but it can be a challenging to determine, specifically with regards to vertical flow through heterogeneous streambeds. Heat tracing via vertical streambed temperature profiles is a technique that has been previously applied to quantify vertical fluxes; however, its use is typically limited to the winter and summer months when temperature contrasts between surface and groundwater are greatest. In this study, vertical temperature profiling was performed up to depths of 50 cm below the streambed during periods of high temperature contrast along a stream reach believed to exhibit groundwater discharge conditions in order to calculate vertical flux. This research seeks to use the vertical temperature flux estimates along with vertical hydraulic gradient data collected beside the heat profile measurements in the streambed to determine vertical hydraulic conductivities based on Darcy's Law. A possible limitation of the technique is the biasing of flux estimates by assuming strictly vertical flow conditions. These calculated vertical hydraulic conductivities will be used to assess the variability in vertical fluxes over time based on observed changes in vertical hydraulic gradient.