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B. The Case Studies Document

1. Origin of the document

The Case Studies Document was produced in 1996 by the Agency for the Assessment and Application of Technology (BPPT) of the Government of Indonesia, in cooperation with the International Environmental Technology Centre (IETC) of the United Nations Environment Programme (UNEP). In that document are recorded much of the basic data and information regarding the two lakes under study at present, Rawa Danau and Rawa Pening (Figure 1).

Relevant information supplied in the Case Studies Document regarding these two lakes is summarised here.

2. Rawa Danau

This small lake lies in an ancient caldera 100km west of Jakarta in Kabupaten Serang in the Province of West Java. The area of the lake was noted as being 11 ha based on 1981 photographic data. The catchment area is 22,620ha, and the caldera is drained by one river the Ci Danau which flows to the coast west of the caldera. The discharge of the Ci Danau is noted as being 5.04m3/sec in the dry season and 20.18m3/sec in the wet season.

The caldera it is surrounded by steep hillsides, including a large area of forest. Rocks are volcanic and soils are derived from these volcanic rocks. The floor of the caldera includes a large area of swamp forest.

An area of 2,500ha including much of the swamp forest was gazetted as a Nature Reserve on 16th November 1921 (erroneously noted as 1929 in the Case Studies Document). The adjacent forest of Gunung Tukung Gede was gazetted as a Nature Reserve in 1979. A considerable area of rice padi was abandoned when farmers were moved out of the caldera under the transmigration program from 1985 to 1987.

3. Rawa Pening

This lake is located in a caldera or volcanic subsidence in the Province of Central Java, in the Kabupaten Semarang and lies about 50km south of the city of Semarang. It lies in a catchment of 25,079ha surrounded by massive volcanos to the south and the remnants of massive volcanos on the south-east and north-west. Soils in the catchment are notably unstable and prone to erosion.

Water flows into the lake from springs on the sides of the mountains and from eight small rivers. The exit from the lake is the Tuntang river. The area of the lake varies seasonally from 2,700ha (wet season) at a height of 463.9m to 800ha (dry season) at a height of 461.5m. The maximum volume of water stored in the lake is 65 million m3.

This is an area with a very high population density, of about 791 persons/sq.km, so the lake has great importance as a centre of economic activities and as a source of water.

4. Value of the Case Studies Document

The Case Studies Document does contain much basic data on the two lakes and these data have been used as the foundation on which further studies were carried out and is used to provide some of the background to the present report. The Document also includes, as far as the two lakes under examination are concerned, a large amount of speculative material regarding the ecological status of the lakes.

As regards Rawa Danau the main ecological problems are listed as siltation following deforestation in the catchment, and changes in land use in the catchment, particularly the development of agriculture, which have resulted in eutrophication. The evidence advanced for eutrophication is the spread of aquatic weeds over the surface of the water. No chemical data are provided to support this opinion.

In regard to Rawa Pening, the very extensive cover of the surface of the lake by aquatic weeds is noted. Significant changes in the biology of the lake are reported to have taken place. Examination of the document does not reveal any hard data to support the latter conclusion. Nor does it reveal exactly what changes are supposed to have occurred.

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