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2.5.01 Adapted technology – an underground hydro-power plant on Java

The southern coast of the island of Java is one of the poorest regions in Indonesia. Water is in short supply, despite the relative abundance of this valuable resource beneath the ground; however, the water flows directly into the sea via a complex underground water system comprising well over 1,000 caves. Scientists in Germany and Indonesia have found a simple solution for one region on Java: a small underground power plant that transports enough water to the surface to supply some 80,000 people.

The approx. 1,400 square metre karst landscape in Java’s Gunung Sewu region is littered with hundreds of interconnected caves and underground streams. Although there is plenty of water beneath the earth, the region’s inhabitants suffer extreme water shortages during the dry seasons due to an absence of appropriate storage facilities – the limited rainfall simply seeps into the karstic ground. Previously, diesel-powered pumps were used to transport the water from the caves up to the surface. Not only does this system use a great deal of energy and carry significant operating and maintenance costs, but the water volume conveyed is not enough to cover the water requirements of private households, local industry and the region’s agriculture.

Cave water

A feasibility study commissioned by the BMBF concluded that it would be technically possible to transport the cave water using hydraulic energy. On this basis, the German- Indonesian pilot project “Accessing and managing underground karst waters in Central Java, Indonesia” was launched in 2002, with the aim of constructing a demonstration hydro-power plant in Gunung Sewu. The project was overseen by the Institute for Water and River Basin Management (IWG) of the Karlsruhe Institute of Technology (KIT) and involved seven institutes from different specialist disciplines as well as industrial partners from the fields of tunnelling, pump and control technology.

Drill site in the karst area

Drill site in the karst area
Drill site in the karst area

Following intensive on-site research, the specialists decided on the (Gua) Bribin cave. It has a capacity of some 300,000 cubic metres and a water flow rate of over 1,000 litres per second, even in dry seasons. The project participants decided to construct a barrage in the cave to dam the continuous flow of water, a part of which was to be transported along a 100 metre riser pipe by means of a small hydro-power plant; this would then supply some 80,000 people in the surrounding shanty towns with Adapted technology – an underground hydro-power plant on Java water. During research and development, a conscious effort was made to employ easily manageable techniques adapted to the needs of the local people and the environment.

Exploration of the cave system

Exploration of the cave system
Exploration of the cave system

Construction work in the cave

Construction work in the cave
Construction work in the cave

To determine the potential water levels and storage volumes, large portions of the cave were measured using state-of-the-art laser technology and the resulting data compiled to form a high-resolution, three-dimensional model. The rock porosity and mineralogical composition was determined through macroscopic and microscopic analyses of samples. This provided the scientists with the means to predict potential water losses and signs of corrosion, thus allowing them to assess the long-term stability of the system. A monitoring network was then installed to enable continuous recording of the water quality as well as hydrological, hydraulic and hydrogeological conditions.

Upon completion of necessary preparations at the project site, the Department of Public Works, Yogyakarta, drilled a first sounding hole (103 m) on the basis of the measurements obtained by the IWG. Following an additional drilling and detailed analysis of the drill samples, work on the access shaft began in 2004; for this purpose, Herrenknecht AG developed a vertical tunnelling machine tailored to local conditions and excavated a shaft around 100 metres deep with a diameter of 2.5 metres. The tunnelling from the surface through to the cave was completed in December 2004.

Pumps instead of turbines

For the construction of the dam with its integrated hydropower plant, a number of different building, material and design variations were examined. As well as focussing on functionality, safety and availability, the project participants were conscious of the fact that the technology employed for the small power plant would have to be adapted to the abilities and expertise of local technical personnel, specifically with regard to control, repairs and maintenance. For this reason, inversely operated pumps developed jointly by the IWG and KSB AG were used instead of turbines. These pumps are affordable, highly robust and easy to maintain.

Work interrupted by earthquake

Upon completion of the planning work, construction of the underground barrage began in April 2005. At the end of 2005, work ceased due to the early onset of the rainy season; shortly after construction resumed in May 2006, the region was struck by a severe earthquake measuring 6.3 on the Richter scale, the epicentre of which was just 30 kilometres from the project site. The site itself escaped relatively unscathed, but the water level rose by approx. two metres following the quake, thus rendering any further work impossible. Professional divers from Germany discovered that the increased water level was caused by fallen rubble after the downstream siphon: over 1,000 cubic metres were blocking the flow cross-section at this virtually inaccessible location. At the end of 2006, German and Indonesian specialists blasted a path through the rubble – work then resumed in June 2007.

Following successful completion of the dam and installation of the first pump module, the first test of the system was performed in August 2008 amid great public interest. Based on saturation processes in the surrounding mountains, it was estimated that it would take one to two weeks to fill the man-made reservoir – in actual fact, the targeted water level of 16 metres was reached after just two days. The first filling of the reservoir was also accompanied by a test of the first pump module, during which the scientists measures a delivery rate of 20 litres per second at the end of the 100 metre vertical pipe – the results were thus in line with expectations. A further four pump modules were then installed, along with an electric system to control the plant.

In March 2010, the project partners were able to hand over the finished system to the responsible Indonesian authority, the employees of which had already received the necessary training to operate the plant. To assess the behaviour of the system in continuous operation and assist with any problems that may occur, the KIT continues to offer its support as part of the follow-up project “Integrated water resource management (IWRM) in Gunung Kidul, Java, Indonesia” (see project 1.3.05).

Project website www.iwrm-indonesien.de

Karlsruhe Institute of Technology (KIT)
Institute for Water and River Basin Management (IWG)

Prof. Dr.-Ing. Dr. h. c. mult. Franz Nestmann
Dr.-Ing. Peter Oberle
Dr.-Ing. Muhammad Ikhwan
Kaiserstraße 12
76131 Karlsruhe, Germany
Tel.: +49(0)7 21/6 08 63 88
Fax: +49(0)7 21/60 60 46
E-mail: peter.oberle@kit.edu
Funding reference: 02WT0424
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Adapted technology – an underground hydro-power plant on Java

A small underground power plant in Indonesia that transports enough water to the surface to supply some 80,000 people
underground dam in the Bribin cave

Project website (only in German)