Imaging the Structure and the Saltwater Intrusion Extent of the Luy River Coastal Aquifer (Binh Thuan, Vietnam) Using Electrical Resistivity Tomography

Abstract

With the growing population and the adverse effects of climate change, the pressure on coastal aquifers is increasing, leading to a larger risk of saltwater intrusion (SI). SI is often complex and difficult to characterize from well data only. In this context, electrical resistivity tomography (ERT) can provide high-resolution qualitative information on the lateral and vertical distribution of salinity. However, the quantitative interpretation of ERT remains difficult because of the uncertainty of petrophysical relationships, the limitations of inversion, and the heterogeneity of aquifers. In this contribution, we propose a methodology for the semiquantitative interpretation of ERT when colocated well data are not available. We first use existing wells to identify freshwater zones and characterize the resistivity response of clayey deposits. Then, we approximate the formation factor from water samples collected in the vicinity of ERT data to derive a resistivity threshold to interpret the saline boundary. We applied the methodology in the shallow aquifers of the Luy River in the Binh Thuan province, Vietnam, where water resources are under pressure due to agricultural, aquacultural, and industrial production. Twenty-one ERT profiles were collected and revealed a much larger intrusion zone, compared to the previous study. Saltwater is present in lowland areas of the left bank over almost the whole thickness of the aquifer, while the right bank is constituted of sand dunes that are filled with freshwater. At a larger distance from the sea, a complex distribution between fresh and saltwater is observed. Our methodology could be applied to other heterogeneous aquifers in the absence of a dense monitoring network.

Hydrochemical, Isotopic, and Geophysical Studies Applied to the Evaluation of Groundwater Salinization Processes in Quaternary Beach Ridges in a Semiarid Coastal Area of Northern Patagonia, Argentina

“…Therefore, the groundwater salinization of Holocene ridges is associated with anthropically induced processes. Intensive exploitation is the main cause of coastal aquifer salinization on a global scale, e.g., [80][81][82][83]. The increased rate of abstraction due to higher water demand has generated significant challenges to sustainable fresh groundwater management, especially to the effective prevention of coastal aquifer salinization [22,27].…”

Soil resistivity measurements to evaluate subsoil salinity in rice production systems in the Vietnam Mekong Delta

“…Geoelectric surveying is a non‐invasive and cost‐effective method for exploring the structure of the earth's subsurface and is used, for example, in groundwater exploration, monitoring landfills or agronomical management (Samouëlian et al., 2005). Common applications of geoelectric surveys are to detect and map groundwater (Mohamaden & Ehab, 2017; Riwayat et al., 2018), identify specific subsurface features, such as gypsum deposits (Gołębiowski & Jarosińska, 2019), and investigate saltwater intrusion into coastal areas and alluvial deltas (Cong‐Thi et al., 2021; de Franco et al., 2009; Gemail et al., 2004; Galazoulas et al., 2015; Nowroozi et al., 1999).…”

Groundwater Salinization and Freshening Processes in the Luy River Coastal Aquifer, Vietnam

“…However, these conclusions were derived from mostly shallow boreholes, without a detailed analysis of the geochemical composition. A recent geophysical study in the Luy River catchment based on electrical resistivity tomography (ERT) [34] revealed the deeper part of the coastal aquifer along the downstream part of the Luy River is mostly occupied by saltwater, whereas the distribution of salinity in the shallow part is extremely variable. Large variations of salinity are observed at short distances, without any apparent correlation with the distance to the Luy river and its tributaries, highlighting a complex distribution of salinity.…”