Predicting the sediment volume of debris flows is the most important factor for designing debris flow control structures and identifying debris flow prone areas. In general, it has been considered that the volume of a debris flow should be controlled by both the sediment transport capacity and removable sediment volume of river bed. Sediment transport capacity should be determined by sediment concentration of debris flow and water volume contributing to debris flow. According to theoretical studies, the “equilibrium sediment concentration of debris flow” has been proposed and verified by the flume experiment. However, Water volume contributing to debris flow has not been fully examined based on field data. Recently, topographic data having a high spatial resolution and rainfall data having a high temporal resolution has been stored. In this study, we estimated sediment concentration of debris flow using LiDAR data and radar rainfall data and then compared with the equilibrium sediment concentration calculated by using the debris flow theory to examined water volume contributing to debris flow. As a result, it is considered that rainfall amount of less than 1-hour may contribute to sediment volume of debris flow.
Imperial University of Tokyo (present the University of Tokyo), which was the first educational organization for studying and learning these fields. After the laboratory was established, two foreign teachers were invited and taught SABO until 1909. In 1909, Dr. Moroto went to Vienna, Austria, to study SABO under F. WANG. He not only studied in Vienna but also visited many places where SABO projects were executed, for example, in France, Germany, Switzerland, Italy, Czech, Poland, Croatia and Montenegro. Through these studies, he gained much knowledge and technology concerning SABO. Just after coming back to Japan, Dr. Moroto became a professor at the Laboratory of SABO, the Imperial University of Tokyo. He produced some technical books and introduced new technology from Europe in many places in Japan. As a professor, he brought up the next generation and promoted research on erosion control technology and forest hydrology. In this paper the footprint Dr. Moroto left are described in the incipient period of modern SABO on the basis of a large literature and field investigation. This paper will contribute to future exchanges between Japan and European countries in the field of SABO based on these historical relationships.
Ohori et. al. (2013) mentioned Ground Penetrating Radar (GPR) applied to check dams was possible to detect weak region of strength of concrete. To clarify 3-D image of surface displacement and distribution of internal clacks in the dam, this article shows that application of SfM-MVS and GPR to a check dam (Sabo dam) with clacks by a debris flow which was occurred in Nagiso Chou, Nagano Prefecture at July 9, 2014. Because a catch dam is concrete structure, GPR is assumed to be a good investigation tool in order to earn 3-D mapping data of internal clacks. Another merits of GPR is portability and easy-to-use in fields. Our result shows the clacks are categorized as mainly three types : 1) a large clack which possibly cause a dam collapse, 2) complexity shape of clacks, and 3) a small size of clacks. Applicable range of our study is that 800 MHz GPR clearly traces continuous clacks inside a concrete dam at least less than 1.0 m depth.
This study investigated heavy rain event which triggered slope failures in Minamiaso-Village, Kumamoto Prefecture after the 2016 Kumamoto earthquake, by using antecedent precipitation indices (APIs) with various half-life times (HLTs). The snake lines for this event did not exceed critical lines (CLs) defined as the past-maximal values. When CLs were reduced by 0.7 times, excesses of the snake lines were detected for many combinations of HLTs. Thus, this study clearly indicated increases in slope failure vulnerabilities in the region which suffered from the 2016 Kumamoto Earthquake.
On 19 May 2017, slope failure occurred and a landslide dam formed at Idegawa watershed, Iiyama city, Nagano prefecture. After three days interval, debris flow occurred several times at Degawa River then partially reached Chikumagawa River. Although there were no loss of lives or property damage, an evacuation advisory has been issued on 20 May, then changed evacuation order on 22 May. After 23 June, this area is under evacuation advisory again. After the disaster, research team was immediately organized by The Shin-etsu Branch of Japan Society of Erosion Control Engineering. In this report, we described the magnitude and the generation processes of landslide and subsequent debris flow occurrence based on a field survey, weather observation data and the airborne laser scanning and videos. Furthermore, we evaluated the effect of the sabo-related facilities and overviewed the monitoring system and emergency measures.
The Aso District was severely damaged by Kumamoto Earthquake that occurred in 2016. In order to rapidly restore the transportation infrastructure and other facilities, we implemented a slope disaster prevention countermeasure construction project of the Aso Ohashi Bridge Area as an emergency project related to Sabo disaster directly under the central government in order to provide immediate measures against this disaster. For the reconstruction work, because of there were concerns on secondary disaster due to aftershocks and rainfall, and because the data on the situation of the site was lacking because it was directly after the disaster, by making use of construction ICT, unmanned construction, remote operation, etc., we carried out land retaining embankment works, as well as rounding works immediately after the earthquake, an area where manned work is possible at the lower part of the slope has been constructed. The background that enabled such a prompt response is because of a business management system that was implemented by the contractee and contractor who worked together as a team. In the business management system that was implemented this time, while simultaneously conducting research, design, and construction in parallel, the team regularly received advice and confirmation by academic experts, and both contractee and contractor worked on measures with a highly organized manner while ensuring mobility. This effort is thought to be effective and useful in future disaster responses, and which may lead to prompt restoration and reconstruction of severely damaged area.