DOI: 10.5884/12560
title: Identification and characterisation of subsurface flows in the Apex River, Iqaluit, Nunavut

description: 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.
description: Purpose: Recent research suggests that climate warming could be impacting the hydrology of Arctic river systems. Long term discharge records in some Arctic catchments indicate a significant reduction in the ratio of maximum to minimum annual discharge, suggesting an increased importance of subsurface flows and groundwater discharge (Burn and al., 2008). In most catchments, the local scale spatial distribution of groundwater fluxes to surface waters, remain poorly known. The distribution and dynamics of local groundwater fluxes to surface waters remain difficult to predict due to uncertainties about the various nested physical controls that modulate subsurface flow and discharge patterns to surface waters (Hinton, 2014). There is a strong need to improve our understanding of the dynamics of subsurface flow processes to better anticipate the impact of climate change on northern freshwater ecosystems. This need extends to the management of northern water resources, where for example the City of Iqaluit has recently proposed drawing water from the Apex River to meet its future needs for freshwater. Here we present a dataset developed in the aim to advance our understanding of the spatial distribution and physical controls on local-scale groundwater inputs to northern surface waters. The data have been developed to address the following specific research objectives; (i) Identification of spatio-temporal patterns of subsurface discharge to the Apex River, (ii) Analysis of the observed spatio-temporal patterns in local subsurface discharge in relation to detailed knowledge of local surficial deposit and topography, (iii) Characterization of the temporal dynamics of subsurface flownets in a selection of hillslope-riparian stream sequences with distinct surficial deposits. The results will be presented simultaneously for the first two objectives, while distinct results will be developed for the third objective.
description: Summary: La localisation d'écoulements souterrains vers les eaux de surface (objectif I) s'est effectué par l'utilisation de traceurs naturels d'eau souterraine (température, conductivité spécifique). La réussite de cette méthode dépend des contrastes entre les caractéristiques des eaux de surface et souterraine, causant des anomalies locales dans les eaux de surface. La cartographie des traceurs naturels a été effectuée à trois reprises à une distance inférieure à 2m de chacune des berges de trois sections distinctes de la rivière Apex. Les cartographies ont aussi été effectuées durant la période de débit de base, lorsque l'écart entre la température des eaux de surface et des eaux souterraines atteint son maximum (Shemin and al, 2011). La cartographie s'est fait grâce à la synchronisation de trois appareils, des senseurs de température (RBR solo) et de conductivité (YSI pro30), permettant la mesure en continu des caractéristiques des eaux de surface et d'un GPS portatif (Garmin Map64) pour la localisation des données. La température et la conductivité spécifique des sections de rivières cartographiées ont été illustrées graphiquement selon la distance amont - aval. L'analyse des graphiques s'est ensuite faite par la délimitation des différentes morphologies du chenal de la rivière, ainsi que des dépôts adjacents. Pour ce faire, une carte détaillée des dépôts de surface de la région d'Iqaluit et un modèle dlévation numérique ont été utilisés. La caractérisation de la variation temporelle des écoulements souterrains directs vers les eaux de surface s'est faite par un suivi des niveaux d'eau mesurés dans un réseau de piézomètres. Trois réseaux ont été installés pour différentes séquences dépôt-zone riveraine-rivière, afin de mettre en perspective l'influence des dépôts et type de surface sur la direction des écoulements souterrain. L'installation des piézomètres s'est faite directement à l'interface avec le plafond du pergélisol et un replacement a été effectué à la moitié de la période de suivi (18/08), qui s'est échelonné du 11/08 au 26/08. L'emplacement des piézomètres ainsi que la surface du sol des trois stations d'étude ont été cartographiés grâce à une station totale optique (Leica Tc805). L'évolution des trajectoires d'écoulement pour les réseaux ont été étudiées par une superposition 3D de la surface de la nappe phréatique et de la surface du sol, obtenues grâce à l'interpolation des niveaux d'eau mesurés et des points d'élévation cartographiés.