9. Shallow/Near-Surface Structural Applications
Determination of Negative Groundwater Withdrawal in Semarang City Area using Time Lapse Microgravity Analysis
Djoko Santoso, Muh Sarkowi and Wawan Gunawan
Geohysical Engineering Research Group, Institute of Technology Bandung, Indonesia.
Abstract
Time lapse microgravity mapping in the Semarang City, Indonesia was carried out six times, June 2002, September 2002, June 2003, December 2003, June 2004 and February 2005. From those six maps we made some different maps of time-lapse microgravity anomaly. The result shows that the zone of positive anomalies and negative zone of anomalies change by time. It is also shows that negative anomalies found occupied nearly 90 percent of the area after nearly 3 three years. It is relevant to the well data of lowering groundwater in this area. Assuming that the positive anomalies correspond to a groundwater addition and negative anomalies correspond to groundwater withdrawal, the change of groundwater table from time to time could be monitored by the shifted of the groundwater table reference line.Since the geologic structure of this area is an alluvial delta, the microgravity anomalies caused by lowering groundwater table irregular. This study gives the understanding about influence of lowering the groundwater table due to groundwater withdrawal and the increasing groundwater table due to groundwater recharge from the surface water, and Semarang city area located in the negative groundwater withdrawal. Therefore, we conclude that the time lapse microgravity technique could be used to determine the negative groundwater withdrawal area as well groundwater recharge area.
Last modified: Thu May 11 13:31:56 2006