Controlling factors of underground river system of karst region in Pacitan Regency, East Java

One of the interesting karst areas is the Pegunungan Sewu, because of the existence of an underground river system that developed below it. The underground river system of Bribin in Gunung Kidul, Yogyakarta is one of the evidence found by previous researchers. In Pacitan District there are karst landscapes that have not been widely studied. Pacitan karst area is in the eastern part of the karst area of Pegunungan Sewu. As the characteristics of the karst region in general, in the Pacitan karst region, there are small hills, vertical hole, closed depressions, rough and pointed surface outcrops, stalactites and stalagmites, and the presence of muddy and water sources. The Pacitan karst area is similar to the Gunung Kidul karst area which has an underground river system. However, the development of underground river systems from these two regions is thought to be different. The purpose of this study is to analyze typical and the controlling factors that influence the development of underground river systems in the Pacitan karst area, East Java. This research was conducted using VES (Vertical Electrical Sounding). The results showed that the typical underground river system that develops in the area of research is more shallow than in Gunung Kidul and suspected to be in the Vadose and it is controlled by the movement of water from the incoming surface through rock fractures.