GEOELECTRICAL METHOD APPLICATION IN DETECTING SEA WATER AND FRESH WATER BOUNDARIES ON THE COASTAL OF TERNATE SMALL VOLCANIC ISLAND

• Main Author: T. Wijaya, Alexandro
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67541
• Institution: Institut Teknologi Bandung

Hydrostatically, water flows according to law of surface fluid equilibrium or passes through subsurface geological structural materials as depositional groundwater recharge. Through electrical properties, water can divide to high and low electrical conductivity, where electrical constituent water materials will increase the density of water. The classification of salinity and electrical conductivity distinguishes water into seawater with a salt content because electrically conducting ions and salt content will increase the density of seawater making higher density than ordinary water. Fresh water deposited into groundwater has low conductivity properties so that the water will inhibit the flow of electricity because water table does not have electrically conducting ions, making the resistivity value higher. Resistivity properties are used to map the distribution of electrical resistance in certain survey areas carried out close to the shoreline in similar measuring parameters for each measurement with form of dipole-dipole and Schlumberger when acquiring apparent resistivity using a certain number of electrodes in pairs in a straight line. The apparent resistivity is then processed using the inversion principle and taking into account the correlation of the measured resistivity and the similar calculated resistivity when the subsurface model from the survey results has been processed in terms of the magnitude of the error. Geoelectric data acquisition was carried out by resistivity imaging and routine inversion provided the actual resistivity value at a shallow depth of 16.4 m – 19.8 m and was able to accurately model the resistivity distribution under the crosssection. The resistivity classification divided into seawater (< 10 ?m), groundwater (10 ?m - 100 ?m), and compacted geological materials (> 100 ?m). The interface begins to form when the resistivity value is 10?m as the meeting zone between seawater and groundwater. Geology plays an important role in the formation of interfaces because fresh water (groundwater) only able to pass through material when it is soft, the space between grains, and the subsurface material is composed of sedimentation products. The contact area angle will be formed based on the trigonometric principle between the closest electrode distance to the shoreline and the depth value perpendicularly.