PERHITUNGAN DEFISIT AIR TANAH DAERAH SEMARANG BERDASARKAN INVERSI ANOMALI 4D MICROGRAVITY

Abstract

The continuous and unbalance withdrawal of ground water in Semarang region with the ground water recharge may cause the decrease/deficit of ground water which can cause land subsidence in the region. This research is carried out to find out the ground water deficit which may be occurred with 4D microgravity. The microgravity measurement was done using gravimeter Lacoste & Romberg  type G1158 fitted with system feedback factor with accuracy of 5 microGal. The gravity measured was corrected by the corrections of tidal gravity and drift to obtain the observation gravity. The 4D anomaly microgravity is a difference of the final and initial of each measurement. The 4D anomaly microgravity was caused by subsidence and the ground water deficit in the ground surface to get the 4D anomaly microgravity which was caused by the ground water dynamic, therefore the subsidence  influenced must be corrected. The corrected subsidence was done by measuring the height using leveling method. The calculation of ground water deficit was done by interpreting 3D anomaly 4D microgravity. The result showed that in the period of 2002 up to 2005, there was ground water deficit of 50.910.000 m³ with deficit rate of 44.500 m³/day.

Keywords: water deficit, microgravity 4D, Semarang