Debris Flows, Floods and Beach Erosion and Their Mitigation

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1.(1)Both Merapi and Mt.Unzen terminated one-cycle activity of dome growth when the amount of extruded lava reached 10^7m^3. (2)Volcanic process prior to eruption revealed by seismic, geodetic and geochemical observations at Merapi is quite similar to those at Sakurajima and Mt.Unzen.(3)Seismicity gap a few kilometers beneath the summit crater are found out at both Merapi and Sakurajima, which may suggest the formation of a magma pocket at the boundary between the basement of volcanic edifice and the layer of volcanic products.2.An observation of debris flow and a topographic survey have been executed at the Bebeng river on the slope of Merapi volcano in Jawa island, and these works clarified that nearly 10 years after the last big event of pyroclastic flows, mass wasting on the slopes is still very active, while the frequency of debris flow is decreasing due to a rapid change in the composition of the surface layer of the slope. One dimensional numerical model has been developed for p … More redicting the occurrence, flow discharge, sediment concentration and deposition area of debris flow. The numerical results show that debris flows cease their movements in the river reaches with the slope of 2-4 degrees.3.Rainfall run off model has been developed and applied to several floods these ten years at the drainage area of Wlingi Dam(2860km^2). It is realized the flood can be predicted if the rainfall characteristics are known. The bed elevation of Brantas river degraded gradually from 1978 to 1989, but began to agrade due to the 1990 eruption of Mt.Kelude, One dimensional numerical model has been developed to predict such bed variations.4.Characteristics of the incident waves in the coasts in south Bali were made clear by analysis of observed data in Sanur. Remarkable feature of wave characteristics is the seasonal differences between in wet and dry. Long and high waves of which height ranges 70-100cm and period 9-12sec (monthly mean of significant wave) attach east coast along south Bali in dry season. In wet season wave height is around 50-70cm and the period 7.5-8sec. Using these results of wave characteristics, erosive properties of coral-sandy beaches in beach reefs have been investigated with numerical models for wave transformation on the coral reef and shoreline changes to make clear the mechanism of beach changes in reef flat and the method of beach erosion control was proposed.5.The temporary houses built after disaster were usually constructed by very cheap level. In Indonesia, the temporary houses were often converted to permananent houses. When we construct the temporary houses in Indonesia, we must take the culture and natural features into consideration. Less