Groundwater and Land Subsidence Monitoring in 3 Mega-Cities, Indonesia, by Means of Integrated Geodetic Methods
Abstract
In urbanized cities, one of the urgent problems is the monitoring groundwater variations especially connected with the land subsidence. In Jakarta, Indonesia, there are more than several tens of observation wells and the monitoring of the groundwater levels have been conducted so far. However for monitoring the variations of groundwater storages, we need additional information about groundwater mass variations as well as land movements which can be obtained by modern geodetic techniques. Therefore we intend to employ a new technique of precise gravity measurements combined with GPS, and InSAR techniques. The gravity changes due to groundwater mass movements are measured as gravity changes by means of precise gravimeters. An infinite water table of one meter thickness causes about a 40-micro gal gravity change. Thus, an accuracy of 10 micro gals or better is required for the hydrologic problems. It is not easy to achieve an accuracy of 10 micro gals by means of a spring-type relative gravimeter, for instance Schintrex gravimeter. We therefore propose a new method to combine absolute gravity measurements and relative gravity measurements. For this purpose, we employ a portable absolute gravimeter A-10, for the measurements at some control points, and employ relative gravimeters of superior portability for the measurements at most points around the control points. Because groundwater variations cause vertical land movements in many cases, it is also important to monitor the height changes at the gravity points. Moreover the rate of gravity changes versus height changes depends on the density of the material which causes the gravity changes, thus it gives important information about the mechanism of the deformation. Therefore we employ GPS measurements for monitoring height changes. We also employ In-SAR images to identify the areas of the subsidence occurs. The first experimental measurements in Jakarta have been conducted in August 2008. The same measurements have been conducted in Bandung and Semarang subsequently. In these cities large land subsidence has been expected as well. We employed A10 (number 17) for the absolute measurements and a Schintrex meter for the relative ones. We plan to conduct the gravity measurements repeatedly for next 2 years with an interval of one, and expect to reveal secular groundwater changes and associated land subsidence in these cities.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H13G1002F
- Keywords:
-
- 1217 Time variable gravity (7223;
- 7230);
- 1219 Gravity anomalies and Earth structure (0920;
- 7205;
- 7240);
- 1829 Groundwater hydrology;
- 1832 Groundwater transport;
- 1834 Human impacts