The region under study, known as ‘Gunung Sewu’ (a thousand hills) is situated along the southern coast of Java, Indonesia. Approximately 1400 km² in area it is host to a large karst area that is internally composed of hundreds of networked caves. Due to these cave structures there is a total exchange of the surface run off and an infiltration through wide branched underground flow systems. These flow systems finally end up as natural springs at the coastline. Due to the fast infiltration of the rainfall into the Karst aquifer and with the absence of suitable water reservoirs, the inhabitants of the Gunung Sewu suffer from water scarcity during the dry seasons.

The current use of water by means of diesel pumping systems cannot meet the growing water demand (supply for private households, trade and agriculture). In view of the expected increase in demand, the existing concept of the water supply is not sustainable both from the economic as well as the ecological perspective. Therefore a sustainable water management system defining a new order of overall development in the entire region is the need of the hour.

Feasibility Study

Within the scope of a feasibility study (2000-2002) on behalf of the Federal Ministry of Education and Research (BMBF), the Institute for Water Resources Management, Hydraulic and Rural Engineering (IWK), University of Karlsruhe carried out an intensive survey to evaluate the possibilities of an underground water management.

The study concluded that, from a socio-economic and ecological point of view, it would be reasonable and also technically feasible to use the underground water resources e.g. by partially damming up the underground water flow by means of a barrage with an integrated micro-hydro power plant and thus

  • Create an underground water reservoir

  • Reduce the pumping height

  • Provide the possibility of water pumping by a hydro power plant

In the realization of the objectives, one of the caves, ‘Gua Bribin’ was found to be particularly suitable. The cave features a storage volume of roughly 400,000 m³. The discharge is considerably sufficient with a minimum available flow of 2000 l/s during the dry seasons. The potential water height after damming in the reachable cave stretch amounts about 15 meters. Also at the downstream of the cave, ideal conditions for the realization of a dam with an integrated micro hydro power plant were found.

Cone Karst formation in Wonosari

Gunung Sewu Precipitation distribution [mm/month]

Cross Section of Karst Aquifer