Fourth Edition
Programme
Young Researchers Overseas Day
15 December 2020
Young Researchers’ Overseas Day Royal Academy for Overseas Sciences Brussels, 15 December 2020
24
Imaging the extent of salt water intrusion in the Luy river coastal aquifer (Binh Thuan) using electrical resistivity tomography (ERT)
Diep Cong Thi
1,3*, Pham Dieu Linh
1,3, Thibaut Robin
1, Nguyen Frédéric
2, Paepen Marieke
1, Huu Ho Hieu
3, Hermans Thomas
1Keywords. — Saltwater Intrusion; Groundwater; Electrical Resistivity Tomography; Luy River.
Summary. — Binh Thuan is one of the driest provinces in Vietnam. During the dry season, seawater in- trudes through estuaries and threatens groundwater resources. The latter are under increasing pressure due to water extraction for agri- and aquaculture. To evaluate the current state of salinity in the shallow coastal aqui- fer, electrical resistivity tomography (ERT) measurements were collected along the downstream part of the Luy river. 21 profiles were collected in July-August 2019 based on the previous saltwater intrusion boundary which was estimated from water samples collected from shallow boreholes in the area. The data were processed to get the resistivity distribution of the subsurface. The results show that resistivity zones lower than 10 Ohm.m and corresponding to saltwater dominate in lowland areas with almost the entire thickness of the aquifer filled with brackish to salt water. On the right bank of the river, the higher elevation dune area contains a freshwater aquifer which limits the intrusion of salt water. At shallower depths, the aquifer displays a complex distribution of fresh and saline lenses. Those variations are correlated with the soil occupation (types of culture) and the irrigation practices. ERT data also reveals the depth of the rock basement. The geophysical observations show that the extension of salt water intrusions is much larger than expected from existing borehole data and is not limited to interaction with the river.
1 Ghent University, 9000-Gent, Belgium.
2 Liege University and KU Leuven, B- 4000 Liège and 3000 Leuven, Belgium.
3 Vietnam Institute of Geosciences and Mineral Resources (VIGMR), 100000 Hanoi, Vietnam.
* Corresponding Author. Email: Diep.CongThi@UGent.be Fig� 1� — Pink line: previously-determined salt water- freshwater boundary with TDS= 1�0 and 1�5g/l; Yellow lines: ERT measurement profiles�
Fig� 2� — Inverse model of 03 representative ERT profiles�
