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H. Urbanisation in the Catchment

The development of Salatiga as a major urban centre near the lake poses a set of problems for the management of the lake. Inspection suggests that enormous quantities of plastic waste and organic waste end up in the rivers coming from Salatiga. Traditionally, garbage is disposed of in kampungs by burning and burial of waste. In the city, this is not so easy. So much is thrown into the nearest river. The river is seen as a free garbage removal system (it costs nothing).

It is recognised that much plastic waste is extracted from the rivers and drainage channels by grids and gratings placed at intervals, throughout the system. From there it is taken to local rubbish dumps. Nevertheless, much plastic waste reaches Rawa Pening, particularly during storms when water may flow over the gratings.

The presence of the city of Salatiga leads to an increased rate of run-off of water from the area. Much of the area is now covered by concrete and tiled roofs, from which rain water flows directly to drains. This water will carry with it chemicals from roads, roofs, gardens, car parks, houses, and markets, along with organic waste from markets and gutters. This urban run-off is not treated in any way prior to reaching the lake.

Such urban run-off is of poor quality. It carries bacteria and viruses from gutters and organic waste. It is laden with toxic chemicals from cans of insect repellents and air fresheners, from tar on roads which contains phenols, from oil, diesel fuel and petrol soaked into road surfaces, from small industries such as panel beating and vehicle spraying businesses, from vehicle service facilities where oil is changed, and from vehicle washing areas where cars, motor bikes, and buses are cleaned in local streams. So it may be toxic to freshwater organisms. It often has a high conductivity (from its salt content) and a low surface tension (from its detergent content).

It is not easy to suggest measures to deal with this. This is a common phenomenon in many industrial countries in the world at the present day. Some components of the urban run-off could be reduced. The washing of bikes, cars and buses in the local streams is unnecessary, if an appropriate facility is provided for this purpose, with an area for allowing the contaminated water to soak into the ground. This waste oil will eventually leak into the drainage system, so ideally it should be removed in drums for appropriate disposal.

It is noteworthy that it is not just the City of Salatiga which may pose problems for the lake. Data obtained some years ago show that the levels of pollution in the rivers flowing into the lake were highest in the rivers coming from Ambarawa. Since that time it appears that extensive military camps have been established on the shores of the lake to the south-east of Ambarawa. There are no data at all on the drainage from these areas in which many tanks and military vehicles could be seen. Presumably there is a considerable amount of oil and petrol involved in the maintenance and operation of such vehicles. We have no information on the disposal of waste from these areas.

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