A Preliminary Appraisal of the Effect of Pumping on Seawater Intrusion and Upconing in a Small Tropical Island Using 2D Resistivity Technique

Abstract

The existing knowledge regarding seawater intrusion and particularly upconing, in which both problems are linked to pumping, entirely relies on theoretical assumptions. Therefore, in this paper, an attempt is made to capture the effects of pumping on seawater intrusion and upconing using 2D resistivity measurement. For this work, two positions, one perpendicular and the other parallel to the sea, were chosen as profile line for resistivity measurement in the coastal area near the pumping wells of Kapas Island, Malaysia. Subsequently, water was pumped out of two pumping wells simultaneously for about five straight hours. Then, immediately after the pumping stopped, resistivity measurements were taken along the two stationed profile lines. This was followed by additional measurements after four and eight hours. The results showed an upconing with low resistivity of about 1–10 Ωm just beneath the pumping well along the first profile line that was taken just after the pumping stopped. The resistivity image also shows an intrusion of saline water (water enriched with diluted salt) from the sea coming towards the pumping well with resistivity values ranging between 10 and 25 Ωm. The subsequent measurements show the recovery of freshwater in the aquifer and how the saline water is gradually diluted or pushed out of the aquifer. Similarly the line parallel to the sea (L2) reveals almost the same result as the first line. However, in the second and third measurements, there were some significant variations which were contrary to the expectation that the freshwater may completely flush out the saline water from the aquifer. These two time series lines show that as the areas with the lowest resistivity (1 Ωm) shrink with time, the low resistivity (10 Ωm) tends to take over almost the entire area implying that the freshwater-saltwater equilibrium zone has already been altered. These results have clearly enhanced our current understanding and add more scientific weight to the theoretical assumptions on the effects of pumping on seawater intrusion and upconing.

Delineation of Seawater Intrusion Using Geo-Electrical Survey in a Coastal Aquifer of Kamala Beach, Phuket, Thailand

“…Furthermore, the fluid electrical conductivity and TDS of each artificial seawater intrusion was measured using a HANNA HI 9813-6 portable meter in order to determine the fluid resistivity ρ f luid . Based on several studies [4,5,[8][9][10][11], resistivity decreases when a formation is combined with seawater. Likewise, the correlation between the formation and fluid conductivities was evaluated.…”

“…Furthermore, the electrical conductivity (the inverse of electrical resistivity) is controlled by the concentration of TDS [7], and resistivity is generally used as an indicator of seawater contamination as resistivity anomalies (i.e., low resistivities) generally indicate a seawater intrusion problem [8]. However, since groundwater chemistry analysis of hydrogeological and pollution research is expensive, labor-intensive, and time-consuming [9], electrical resistivity imaging (ERI), accompanied by limited groundwater chemistry data are increasingly being used as an effective tool because they are a non-destructive and efficient method for characterizing the subsurface, especially for quantitative and qualitative assessments of subsurface problems [10]. Sherif et al [7] applied geoelectrical and hydrogeochemical studies to delineate seawater intrusion in the outlet of Wadi Ham, UAE.…”

“…The authors successfully determined the present of brackish and saline water zones with resistivity values ranging from 1 to 30 Ohm-m in their study area. Similarly, Kura et al [9] conducted ERI to study effect of pumping on seawater intrusion in the coastal area near the pumping wells of Kapas Island, Malaysia. Their result showed the seawater intrusion from the sea coming towards the pumping well with resistivity values ranging between 10 and 25 Ohm-m.…”

“…In recent years, several studies have been conducted around the world to elucidate the spatial distribution of seawater intrusions, and to delineate the areas characterized by the presence of seawater, and how that influences groundwater resistivity values. Moreover, strategies have been implemented to control the salinization of groundwater [4,5,[8][9][10][11]. For example, Costall et al [12] researched and proposed a comprehensive study of ERI along coastal margins, which was validated with substantial evidence from seawater monitoring wells.…”

Evaluating the Application of Electrical Resistivity Tomography for Investigating Seawater Intrusion

“…R. de Franco et al [5] performed ERT on the coastal boundary of the Venice Lagoon in southern Italy and found that some factors in the environment, such as rainfall and tide, also affect the resistivity changes. Nura Umar Kura et al [6] used ERT to initially evaluate the effects of seawater intrusion and upconing in a small tropical island. Oyeyemi et al [7] used ERT to investigate seawater intrusion in alluvial areas in southwestern Nigeria.…”