Hydrological River and Coastal Field Investigation for Integrated Water and Sediment Management in Three Basins in Java and Sumatra, Indonesia

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This research dealt with river basins as a whole system consisting of mountain slopes, rivers and coastal zones, in order to find out best practices for integrated water and sediment management. Water and sediment movement in the Semarang, Brantas and Toba basins in Indonesia was investigated through field survey and hydrological and hydraulic computer simulation models. Collecting meteorological, hydrological and oceanographic observation data as well as social environmental data, this research tried to account for the interactions between human activities including land use change and mass movement such as water and sediment, and to explain the mechanisms of occurrence of disasters caused by river bed and river mouth variation due to floods and sedimentation. The following results are obtained through the field survey, collaborative research and information exchange with Indonesian researchers.(1)In Semarang basin in Central Java, which has steep slopes with erodible soils and is suffering from floods and sediment problems in coastal zones, degradation of coastal environment and beach erosion are investigated with numerical simulation models. (2)A distributed hydrological storm-sediment-runoff model was established to predict flood runoff and sediment yield from volcanic hill slopes and agricultural lands in the Brantas River basin. Hydraulic models for analyzing river bed variation were also developed and improved. (3)Lake Toba located in the northern part of Sumatra Island has been receiving less inflow recently and its water level is lowering. To investigate this phenomena, the bed form and elevation of lake bottom are surveyed by echo-sounder and a hydrological rainfall-runoff model was constructed. (4)In Central Java, another research activity estimated sediment yield and debris flow from a valley of Mt.Semeru on the basis of hydro-geomorphological analysis and field survey.