Suspended sediment in mountain rivers can be observed using two methods : one measures the suspended sediment concentration directly by sampling the water ; the other is indirect measurement using a turbidity meter. The results of this study are as follows. 1) The turbidity meter can only measure the wash load (particle size<0.106 mm). 2) Although the suspended sediment can be easily observed by bucket sampling of water, which is also suitable for ascertaining the characteristics of the wash load, this method is not suitable for continuous monitoring. In contrast, observations obtained with a turbidity meter can be used for continuous monitoring and are appropriate for monitoring the basin but are not suitable for obtaining stable data. 3) It is important to observe the concentration distribution of suspended sediment in the vertical direction by using multistage suspended sediment samplers for a variety of considerations.
When a volcano erupts and snow deposits in the vicinity of the volcano, pyroclastic flow and surges melt the snow and trigger catastrophic lahar. To mitigate the inundation area, it is important to set an appropriate hydrograph as boundary condition. However, the process of heat exchange between the pyroclastic material and snow is not so clear that drastic assumptions are often adapted. Sublimation occurs whenever pyroclastic material contacts with ice or water and could be treated physically. Hence, to estimate physically the heat energy of sublimation, experiment and heat conductivity analysis are carried out. In the analysis, sublimation of ice is calculated with Hertz-Knudsen formula. The results indicate that the sublimation of ice should be considered in order to predict precisely the time series variation of snow depth, and about 83 percent of heat energy from hot gravel supplies to snow.
Particle-based simulations are widely used in fluid engineering applications such as analysis of river flows, tidal waves and tsunamis. In this work, Position Based Fluids (PBF), which is particle-based fluid solver that is also capable of handling rigid particles, is used for a driftwood simulator in three dimensions. In the simulator, stream flows are expressed by fluid particles and driftwoods by rigid particles of PBF. The result of the waterway experiment conducted by Shibuya et al. in 2010 is compared with the results obtained from the driftwood simulator ; two problems are identified. One is that the particles pass through the wall instead of colliding against it, and the other is that there is no surface friction between woody debris in contact. To solve the latter problem, spring elements are incorporated between woody particles in contact, and the simulator obtains suitable results for Shibuya's experiment.
Mass wasting and landslides have claimed sizable human casualties in Japanese archipelago for a number of years. Herein lies the importance of mitigation works (thereafter “sabo works”). Nevertheless, the cost performance of sabo works has not seen an upward trend. Financial constraint drives us to make further effort to upgrade now age-old engineering methods substantially. This case study describes an attempt to apply a combination of drainage pump and air-vacuuming pump, a kind of active drainage method. The study leads to a comprehensive cost performance analysis in relation to gravitational drainage wells with lateral boreholes, which are in wide use. The combination allows us to get over the engineering depth limits of pumped wells, whether the pumping apparatus may be put down at the bottom end or on the ground surface. Multifaceted evaluation of field testing during two consecutive seasons shows that the combined application of pumps could have advantages, in terms of cost, to existing gravitational drainage methods about three to five times, not only for short time but also for forty-year period. Their site specificity is to be taken into consideration carefully throughout the analysis.
After the Kumamoto Earthquake in April 2016, a lot of secondary sediment movements were induced by rainfall and secondary sediment disasters were caused by them from April 16th to the end of July in Kumamoto prefecture, especially in the Aso volcanic range. Hence, field investigations and reconnaissance were conducted four times by the Japan Society of Erosion Control Engineering to clarify the actual conditions of the phenomena of secondary sediment movements and secondary sediment disasters. The various results and information obtained through those investigations were reported as the secondary report concerning characteristics of rainfall after the earthquake, distribution of secondary sediment movements, geologic-geomorphologic characteristics of secondary sediment movements, features of secondary disasters, and the efficiency of Sabo facilities in these disasters.
Debris runoff occurred due to heavy rainfall of Typhoon MALOU in Kakidairasawa, Numata City, Gunma Prefecture on Sept. 7, 2016 and caused damage on 4 houses. After the disaster, research team was immediately organized by the Kanto Branch, Japan Society of Erosion Control Engineering with the aim of investigating the processes of generation, flow and deposition of debris movement and clarifying the actual conditions of debris disaster. Following features are observed : 1) the debris runoff was caused by the short period torrential rainfall, 2) the debris runoff was affected by large amount of surface runoff, 3) pumice layers were exposed by the erosion of stream bed, 4) a woody debris dam was formed by deposit of logs and sediment in the stream.