The coastal areas of Phuket Island are facing the risk of seawater intrusion, because intense anthropic activity due to urbanization and the expansion of tourism influences coastal hydrologic systems. Indeed, the Kamala sub-district—on the western part of Phuket Island—is a well-known and attractive destination for tourists. Previous research indicates that there is likely to be a seawater intrusion in Kamala. The main purpose of this study was to delineate the seawater intrusion problem in a coastal aquifer in Kamala. Geo-electrical surveys of four lines were successfully conducted in the study area. Two-dimensional (2D) inversion models from the resistivity data show high-resolution subsurface resistivity anomalies of seawater intrusion. The concentration of the seawater intrusion decreases eastward toward the inland areas. Based on a sample measurement, the contaminated zone of seawater has a resistivity value smaller than 30 Ohm-m, and the empirical relationship between the formation conductivity and fluid conductivity of the study area was established. Finally, time-lapse Electrical Resistivity Imaging (time-lapse ERI) was conducted to prove that there was no presence of clay layers in study area; thus, the low resistivity plumes (smaller than 30 Ohm-m) were scientifically interpreted as being seawater intrusion.

Phuket is well-known around the world as a popular tourist destination. Tourism-related population growth depends more on groundwater as the only available source of potable water in Phuket. The proper precautions must be taken to reduce the risk of spending large sums of money in sinking abortive boreholes, and a groundwater potential map would enhance the success rate of future groundwater exploration and exploitation in the study area. Geoelectrical surveys were carried out in this study to collect electrical properties of the subsurface, and the Dar-Zarrouk parameters (DZP) were calculated using the geoelectrical data. The first thematic groundwater potential map was constructed using the interpretation of DZP, while the second thematic groundwater potential map was created using the basis maps of the depth-of-basement and aquifer thickness parameters. Finally, two thematic maps based on geographic information system (GIS) environments were overlaid on a groundwater potential map of Phuket. However, in order to provide a reliable assessment of groundwater potential, time-lapse electrical resistivity imaging was used to confirm the area of the high-potential zone indicated on the map. The map created by this study is aimed to act as a reference for future groundwater exploration and exploitation, preventing water supplies from becoming unsustainable through botched borehole drilling for groundwater production.

Shale rock formed from small clay particles, and shale compaction is an essential factor to estimate shale reserves. The classical Athy’s model has been used to obtain the shale compaction curve to describe the relationship between porosity and depth, an essential input data for basin modelling. But recent studies revealed that burial time, among other factors, should be considered and that geological age is another important factor in some regions. This is because geological and lithological histories are crucially different among geological ages. This study employed the newest data of Thailand shales and confirmed that different geological ages (Cenozoic, Mesozoic, and Paleozoic ages) require different shale compaction curves by estimating numerical geological time with the relationship of velocity and depth in each geological age. We obtained empirical models of the shale compaction curve of each geological age by multi-linear regression. The standard curve of shale compaction with the relationship among porosity, depth, and time, proposed in a previous study, was also re-affirmed with the newly obtained models.

Groundwater is the dominant source of water supply on Phuket island, Thailand. The water demand on Phuket has been increasing due to rapid urbanization and population growth. A scarcity of freshwater and over-extraction of groundwater may shortly become severe problems for Phuket. Geoelectrical data obtained by Vertical Electric Sounding (VES) were employed in this study to estimate the Dar Zarrouk parameters of the study area. Twenty-four VES stations were set up using Schlumberger configuration with a 1.0 m minimum spacing. The lithology layers from 24 unpublished borehole data indicating each subsurface layer were validated with the resistivity data obtained from VES. The geoelectric profiles gave a maximum of three layers with varying resistivities and thicknesses across each VES station. Two parameters (longitudinal conductance and transverse resistance) of the Dar Zarrouk model were calculated from VES data to generate the thematic maps in a GIS environment, thus the groundwater potential in Phuket Island was represented as a single map by using the weighted overlay technique in ArcGIS, based on both longitudinal conductance and transverse resistance. The groundwater potentials were classified into three potential levels (low, medium, and high). The results reveal that the highest groundwater potential areas are isolated and in specific locations, while the majority of area has medium level groundwater potential. Finally, the low potential zones are in the flank and the top parts of the study area.

Phuket is well-known around the world as a popular tourist destination. Tourism-related population growth depends more on groundwater as the only available source of potable water in Phuket. The proper precautions must be taken to reduce the risk of spending large sums of money in sinking abortive boreholes,