Geophysical investigation of the shallow aquifer and its vulnerability in the Cu Chi rural district, HoChiMinh city region, Vietnam
- Authors
- Publication Date
- Feb 22, 2024
- Source
- HAL-Descartes
- Keywords
- Language
- English
- License
- Unknown
- External links
Abstract
Ho Chi Minh City (HCMC) region in the south of Vietnam faces significant challenges from climate change and subsidence, with more frequent flooding, and threat of saltwater intrusion. As a proactive measure for future mitigation and development, particular attention is being paid towards sustainable groundwater resources. The northwest, characterized by high terrain and identified as the regional recharge area, is earmarked as a potential crucial groundwater reserve for the future.The primary objective of this research is to understand better shallow groundwater resources and their vulnerability to human practices. The second objective is to evaluate several geophysical methods for hydrogeology in the sedimentary geological context of the Saigon River area. An extensive geophysical field investigation was conducted using Time-Domain Electromagnetic (TDEM), Frequency Electromagnetic (FEM), and Electrical Resistivity Tomography (ERT) methods, being evaluated for their sensitivity to clayey layer detection using numerical modeling prior to the survey. These methods proved effective in characterizing the geometry of the aquifer and aquitard system to a depth of 150 meters for TDEM method, very sensitive to electrically conductive clayey layers. The research revealed that the absence of a surface clay layer thus facilitates groundwater recharge, posing a risk of surface pollutants easily infiltrating the aquifer. Moreover, deeper clay layers are discontinuous, increasing the vulnerability to the downward spread of contaminants. The research also points towards a new conceptual model of the aquifer involving geological transgression-regressions scenarios to explain the spatial distribution of the clayey aquitards, showing meanders and floodplains of the ancient Saigon River at depth.Innovatively, the Nuclear Magnetic Resonance (NMR) method was also employed at the laboratory scale to classify the aquifer using core extracted from boreholes tests. Coupled with grain size analysis, the results show that the shallow aquifer is fine-grained. As field-scale NMR was unsuccessfully applied due to high noise conditions, analyses with pumping and tracer tests gave additional data, leading to the conclusion that NMR results are still preliminary as several improvements have to be made regarding noise reduction and specific yield determination.For the future, the research paves the way for constructing 3D hydrodynamic models for sustainable exploitation. Vadose zone models will also facilitate the evaluation of pollution in the water table. Finally, this research highlights the efficiency of resistivity-based geophysical methods for sedimentary shallow aquifers characterization in Saigon River and HCMC regions. Combined with hydrogeological methods, future geophysical studies will help to address future groundwater challenges and contribute to the south of Vietnam’s resilience against climate change impacts.
