CONTROLLING SEAWATER INTRUSION BENEATH SEMARANG COASTAL URBAN CITY USING GEOPHYSICAL SURVEY AND HYDROGEOCHEMISTRY DATA

As the largest areas in Central Java Province, Semarang has experience coastal inundation from local flood inundation, river flood and sea water tide flood. Moreover, the city experiences long-term seawater intrusion. Investigation of seawater intrusion is a must to control the actual condition. Geophysical survey will provide a subsurface condition that combines the hydrogeochemistry data in controlling seawater intrusion. Resistivity data was collected using the Wenner array. The RMS error computed for iterations of the resistivity value varying from 7.7 to 40.4% with the total depth up to 39.6 m depth in the inverse model resistivity section. Based on the geoelectrical profile, 5 of 10 locations, i.e. SMG-1, SMG-2, SMG-3, SMG-5, and SMG-7 conducted very low resistivity value. The maximum Electrical Conductivity/EC value was 8,810 μS/cm. Integrated Geophysical survey and hydrogeochemical analyses provided the study area into three groups related to the seawater intrusion which are uninfluenced, moderate influenced, and highly influenced.