Horizontal gradient analysis of gravity data for subsurface fluid flow identification (case study: Cilincing, north jakarta)

Jakarta is a large city with a 10.37 million population. Most of the clean water needs are provided via groundwater. This might be a problem for some areas with groundwater conditions such as brine, or even salty water. The salt-water issue in Jakarta is not uncommon. Many researchers have conducted their studies on this topic from many perspectives. They are all divided into 2 main general conclusions, saltwater happens because of intrusion and saltwater is there because it is connate water. This study aims to give a new perspective on understanding the salt-water issue. Methods used for this study are gravity measurement to get a horizontal gradient value. The other is groundwater well sampling to measure the value of pH, salinity, conductivity, and water table elevation. These methods will be comprehensively interpreted to get the direction of subsurface fluid flow. Results from salinity and conductivity of groundwater show more salinity and conductivity in the North direction and less on the South one. Gravity data and the geological map also suggest that there is a fluid flow coming from North East to South West. All of these methods used in this study have come to one conclusion, there is water flowing from the sea to the land, therefore there is a most likely saltwater intrusion on the region where this study is conducted.