Field observation on integrated sediment management in Brantas river basin, Indonesia

点击翻译按钮获取中文摘要

The information available to the integrated sediment management of the Brantas river basin was examined by the field survey, field observation, and the simulation of bed variation. Particularly we investigated the topographical change of the main river after the eruption of Mt.Kelude in 1994 and the sediment yield and transport in M.Semeru basin considering the influence of sand mining and deforestation as human impact. Immediately after the eruption in 1994, a large amount of sediment flowed into the main river rapidly from the tributaries and a sever bed aggradation took place and the bed material became much finer. The sediment discharge from the tributaries immediately after the eruption is an essential information for the sediment management. As a result of the analysis, it was found that the condition is evaluated with the local hydraulic condition and the grain size distribution of the produced sediment. After the eruption, however, the tendency of bed variation changed quickly to the opposite. According to our survey, we can recognize the sediment movement in the tributaries even in rainy season and sand mining was very active in the main river and the tributaries. It is seemed that sand mining and irrigation cause the decrease in sediment supply and water discharge and consequently the bed level became much lower and the bed surface was covered by armor coat in the main river and tributaries. Field observation on suspended load in the main river has indicated the sediment yield of fine sediment was decreasing gradually after the eruption, but it has recently increased again. One of the reasons is the deforestation and more active sand mining. Also, field survey in Lesti river has indicated the suspended load concentration is very large in early stages of the rainy season because the farmland is disturbed by cultivation.