Identification and characterisation of subsurface flows in the Apex River, Iqaluit, Nunavut

The localization of groundwater input in the Apex River have been possible by using groundwater tracers (temperature, specific conductance). The success of this method depends on the contrast between groundwater and surface water characteristic, causing anomalies in surface water characteristics when groundwater discharge occurs (Stonestrom, 2003, Vaccaro, 2006). Three mapping of groundwater tracer were performed within less than 2m of each bank of three distinct sections of the Apex River. These mappings were made during the baseflow period of the river, where the highest difference between surface water and groundwater is observable. Synchronized high resolution temperature probe (RBR solo, accuracy 0.02°C), conductivity probe (YSI Pro30, accuracy ± 0.05% of reading) and a GPS (Garmin Map64, accuracy 3m), were used for measurements and spatial localization. The temperature and specific conductance of the river reach profiles were graphically illustrated according to the upstream - downstream distance. The analysis of the graphic was subsequently made by delineating the distinct reach morphology and surficial bank characteristics. To this end, a detailed surficial geology map of Iqaluit area and digital elevation model (resolution 1m) have been used. The characterization of the temporal dynamics of subsurface flownets was made by monitoring shallow supra-permafrost groundwater with piezometer networks. Three networks were installed across hillslope-riparian stream sequences of distinct deposits. The installation of the piezometers was made directly at the interface with the frost table, and a replacement of the piezometers depth has been done at the half of the period monitored, which covered the August 11th to the August 26, 2015. Water levels in the piezometers were measured daily with a manual water level deeper. Location of the piezometer and the ground surface of the network were mapped with an optical total station (Leica TC805) to allow the spatial representation of subsurface flow trajectories evolution. The water level measured and the elevation points sampled with the total station have been interpolated to allow a 3D representation of the water table and the ground surface. Superposition of the surfaces shows the areas of positives hydraulic gradients, which can indicate the zones where subsurface flows are concentrated in relation with the network topography and the river.