Sediment budget and estuarine circulation on the Brantas River Estuary, East-Java, Indonesia

Moetariyono, R. Didiek (1992) Sediment budget and estuarine circulation on the Brantas River Estuary, East-Java, Indonesia. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Brantas River with a catchment area of 12,000 sq km is the largest river in Eastern Java, Indonesia. Heavy monsoon rains create flooding and the sediment load is enhanced by fine volcanic ashes from Kelud Mountain, located in the middle of the drainage basin. Flood controls were placed on the river to minimize excessive floods. Every year large quantities of sediment enter the estuary. Some settles within the estuary, particularly the deltaic region, but a significant portion flushes directly to the surf zone bordering the Madura strait. Much of the material is redistributed in estuary areas as the fresh water flow subsides. – Topographical changes caused by this sediment load became more significant after a manmade channel, the shortcut channel, was dredged to bypass the existing delta. – Field measurements and collation of existing data were carried out during the dry season of 1991. Data were collected relating to tides, sediments, waves, currents, topographical changes and fresh water discharge with a view to understanding sediment movement and budget in the estuary and any chronological sequences. Theoretical analyses were also conducted to evaluate sediment inflow by tidal and longshore currents, river mouth processes and delta growth. – The study has shown that significant changes have taken place, that the processes are ongoing and that the discharge capacity of the two main channels is decreasing. One specific aspect of the study shows that since the dredged shortcut channel has been completed, the major delta growth has moved from the original river mouth to that of the shortcut channel. Consequently, new geometric formations of the surf zone have been developed. Now, the shortcut channel has become a main channel while the original river becomes shallower and narrower year by year. – Sedimentation in the estuary is an important aspect of flood and sediment management on the Brantas River. Further work is required to adequately determine the sediment budget and estuarine circulation to permit development in the Brantas estuary.

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