In areas where volcanic activity has occurred and volcanic sediment has accumulated in rivers, significant caution should be taken in terms of the possible occurrence of disasters associated with debris flows. The use of a real-time detection and warning system, in combination with conventional erosion control measures, is an effective approach in mitigating such disasters. The advent of sensing technology that is able to detect debris flows using vibration sensors will contribute to the development of an automated real-time detection technique. Waveform analysis and Fourier spectral analysis techniques are adopted in developing this technology. We developed a detection method by investigating vibration records at the Hakodate erosion control project. For verification, the method was applied to data from the Nojiri River, which is under the administration of Osumi River and the Nationalway Office. For an event that occurred on 10 July 2004, a predominant frequency change was discovered in synchronization with wire-sensor cut times recorded by video-camera recorders located on check dams. In more precise terms, when the wire-sensors were cut the dominant frequency of the waveform shifted from the high-frequency range (above 100 Hz) to the lowfrequency range (below 50 Hz), and the spectrum intensity increased. This phenomenon depends on the conditions of stream flow.
Nagasaki is well-known as an area with many sediment-related disasters. On this point of view, installation of erosion control facilities has been pushed forward from the past. However, the installation ratio of the facilities has not always been sufficient because there are too many points. Under the above conditions, for installing the erosion control facilities effectively with limited budget, it is important to consider a priority of an improvement project at each vulnerable spots. Therefore this study performed examination based on an evaluation result by Data Envelope Analysis(DEA) about priority of dangerous spots for sediment-related disasters in Nagasaki. In this study, we used a new factor to evaluate importance of vulnerable spots for sediment-related disasters as well as a factor used in a study example of the past. As a result, a priority that reflects the characteristics of its hazard and importance at each spots can be evaluated. It is recognized that there is a correlation between the evaluated priority and past disaster histories or counter -measure works. This shows that the DEA is proper for priority evaluation and very effective technique for studying erosion control facility improvement projects.
Temperature conditions were evaluated inside the Kaliadem village shelter, which was buried by the main body of pyroclastic flow from the Mount Merapi eruption on June 14, 2006. Numerical analysis of one-dimensional steady state, two-dimensional steady-state, and non-steady-state heat transfer into the shelter was performed to determine the effectiveness of insulation materials lining shelter doors, the changes in doors' thermal conductivity, and the effects of door thickness on temperature reduction. Results show that average temperatures inside the shelter greatly exceed human body temperature in every scenario except when doors are lined with cellulose insulation. When the shelter is buried by a pyroclastic flow with a maximum temperature of 800℃, the average temperature inside the shelter can be reduced below human body temperature if double doors are lined with at least 85 cm of cellulose, or triple doors are lined with at least 55 cm of cellulose.
In the artificial deposits prepared by experimental sediment discharge at Tateyama Caldera Sabo Museum, the maximum principal axis, ‘Kmax', of anisotropy of magnetic susceptibility (AMS), was found to be parallel to the current direction.The results indicated that the magnetic particles in the deposits were arranged in the current direction. This was concordant with observation under the reflecting microscope on the polished block of the deposit. The AMS study was also applied on the mountain stream deposits of the Kiso Mountains. The Kmax of AMS was parallel to the mountain stream direction which transported the deposits. The AMS method seems to be useful in the study of transportation and depositional process of sediment discharge.
Hydrophone has been used to measure bedload transport intensity by counting the number of pulses made by hitting of sand and gravels to a steel pipe. When sediment transport rate is high, the sound level is continuously high and never drops low resulting in that the number of counting becomes low or zero. Sound level is recorded to know sediment transport intensity instead of pulses when sediment transport rate is high. The method was adopted in the Waru-dani torrent, a branch of the Jinzu River. The relationship between acoustic energy and pulses were analyzed. The acoustic energy was well recorded and showed sediment transport intensity as well as the record of pulses. It was found that there is an appropriate amplification. As we have not obtained good data for high sediment transport rate, we will continue the measurement.