History of Development and Attendant Environmental Changes in the Brantas River Basin, Java, Indonesia, since 1970
The Brantas River is the second largest river on the island of Java which has undergone major changes in the past decades because of the demands of an evergrowing population. Water management measures were mainly designed (i) to provide flood protection, (ii) to provide raw water for irrigation, households and industry, and (iii) to generate hydropower. The objective of this paper is to delineate the history of development and attendant environmental changes since 1970 as well as to address the effects of a mud volcano eruption in 2006. Data from three gauging stations representing the upstream, midstream and downstream portions of the Brantas River were chosen to display patterns in discharge (1970-2003) and in nutrients (1991-1997). Overall discharge decreased over time at all stations with the strongest decrease in the downstream portion. The amplitude of seasonal changes in discharge was highest in the downstream portion. Dissolved inorganic nutrient concentrations increased slightly downstream as a result of land use. An eruption of a mud volcano in 2006 added to the initially high sediment load of the river. A portion of the mud was directed into the river leading to extremely high suspended matter and low dissolved oxygen concentrations. As a large part of the high suspended sediment load, already settled in the river, dredging was initiated in order to avoid blocking of the river. The dredging material was used for land reclamation. The high nutrient and sediment loads of the Brantas River are to a large extent the result of intensive human activities in the catchment like hydrological alterations and land-use change. Extreme natural events like the mud volcano exacerbate the consequences of human alterations on the water quality and biogeochemistry of the river.
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