Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 351 – 358
1Mining Engineering Department, Bandung Institute of Technology (ITB), Indonesia
2Geology Department, UPN “Veteran” Yogyakarta, Indonesia
Abstract: The Gunungsewu Area in Central Java, Indonesia, has been suffering from water shortage since time immemorial, although the precipitation in the region concerned and surroundings is known to be adequate (2,000 mm/year average). This region is controlled by a karstic geology with conduits, dolines, caves, and subterraneous rivers, and very permeable rock formation, causing most of the rainwater in this area to be directly absorbed into the ground. There is a homoclinal structure dipping southward that conducts groundwater to discharge enormously into the Indian Ocean. The Gunungsewu limestone is composed of reefs and bioclastics, which based on their different physical characteristics in the field, can be classified into chalky limestone called caliche and karstic limestone. Groundwater level in the bioclastic limestone is at 5-10 m depth, whereas in the reef limestone it is able to reach 150 m depth or more. The existence of caliche and karst in Gunungsewu enable the rock formation to be divided into non-karstic aquifer with diffuse flow and karstic aquifer with conduit flow.