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Title: Time-lapse cross-hole electrical resistivity tomography (CHERT) for monitoring seawater intrusion dynamics in a Mediterranean aquifer
Author: Palacios, Andrea
Ledo Fernández, Juanjo
Linde, Niklas
Luquot, Linda
Bellmunt Traver, Fabián
Folch, Albert
Marcuello Pascual, Alejandro
Queralt i Capdevila, Pilar
Pezard, Philippe A.
Martínez, Laura
del Val, Laura
Bosch Ros, David
Carrera, Jesús
Keywords: Tomografia
Mediterrània (Mar)
Hidrologia d'aigües subterrànies
Mediterranean Sea
Groundwater hydrology
Issue Date: 30-Apr-2020
Publisher: European Geosciences Union (EGU)
Abstract: Surface electrical resistivity tomography (ERT) is a widely used tool to study seawater intrusion (SWI). It is noninvasive and offers a high spatial coverage at a low cost, but its imaging capabilities are strongly affected by decreasing resolution with depth. We conjecture that the use of CHERT (cross-hole ERT) can partly overcome these resolution limitations since the electrodes are placed at depth, which implies that the model resolution does not decrease at the depths of interest. The objective of this study is to test the CHERT for imaging the SWI and monitoring its dynamics at the Argentona site, a well-instrumented field site of a coastal alluvial aquifer located 40 km NE of Barcelona. To do so, we installed permanent electrodes around boreholes attached to the PVC pipes to perform time-lapse monitoring of the SWI on a transect perpendicular to the coastline. After 2 years of monitoring, we observe variability of SWI at different timescales: (1) natural seasonal variations and aquifer salinization that we attribute to long-term drought and (2) short-term fluctuations due to sea storms or flooding in the nearby stream during heavy rain events. The spatial imaging of bulk electrical conductivity allows us to explain non-monotonic salinity profiles in open boreholes (step-wise profiles really reflect the presence of freshwater at depth). By comparing CHERT results with traditional in situ measurements such as electrical conductivity of water samples and bulk electrical conductivity from induction logs, we conclude that CHERT is a reliable and cost-effective imaging tool for monitoring SWI dynamics.
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It is part of: Hydrology and Earth System Sciences, 2020, vol. 24, num. 4, p. 2121-2139
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ISSN: 1027-5606
Appears in Collections:Articles publicats en revistes (Dinàmica de la Terra i l'Oceà)

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