Recently, many large-scale debris flows have occurred due to the torrential rainfall under climate change, and the steel open dams have been occasionally damaged. To this end, this paper proposes a safety verification method on the load-carrying capacity of steel open dams against the large-scale debris flow (level Ⅱ load). In this method, the maximum load-carrying capacity of a steel open dam should be larger than the required load-carrying capacity of a steel open dam, which means the necessary resistance force of a steel open dam against level Ⅱ load and it is found by using the energy constant law. As the numerical examples, the maximum and required load-carrying capacities of three steel open dams with different structural shapes (i. e., truss type, frame type and mixed type) are investigated by performing an incremental elastic-plastic analysis (pushover analysis). As the computational results, it was turned out that the truss type has the largest strength, while the frame type has the largest ductility and the mixed type has the intermediate behavior. It was verified that all three steel open dams were satisfied with the safety criteria on the load-carrying capacity. It was also inspected if the energy constant law may be applied to the steel open dams under the level Ⅱ load or not, by comparing the response displacement obtained in the energy constant law with the displacement which is found by the pushover analysis at the same energy condition. Finally, the redundancy (reserved strength) of each steel open dam is examined and compared with the required load-carrying capacity of each steel open dam. It was recognized that the redundancy of frame type is the largest, next one is mixed type, and last one is truss type, which are the same tendency as the margin of required load-carrying capacity against the maximum one.

While still protecting the area from sediment-related disasters as active facilities, historical sabo facilities are also used as outdoor educational opportunities that convey the local history along with how to deal with disasters, and are used as a local resource in regional revitalization. However, as for the utilization of these historic facilities, not every location is fully aware of the value they hold, nor are they all being used for such purposes. This time, local residents were surveyed as to the present state of historic sabo facilities, along with the challenges they face; specifically targeting both the Bannai River and Hikagesawa (Myoko, Niigata), which are considered the pioneers of historic sabo facilities throughout the Niigata prefecture, as well as the Kamakurasawa River (Minami Uonuma, Niigata), which takes second place in terms of age. This study outlines the current state of the utilization of historic sabo facilities, and considers the issues of utilization in comparing the two locations. These two historical sabo facilities have different utilization situations. Based on the research results on the construction history and technical background of historical sabo facilities so far, we will reveal the issues in the levitation of historical sabo facilities from the questionnaire survey and interviews. Based on them, we considered conservation utilization, maintenance and regional activation of historical sabo facilities. As a specific correspondence content, we proposed the organization of a resident organization, maintenance of activity base facilities, and regular events and advance the levy of historical sabo facilities.

Landslides are typically triggered by earthquakes or rainfall, and occasionally slope changes occur due to the continuous effect of rainfall or snowmelt. Significant amounts of sediment from earthquake-induced landslides usually flows downstream for a long period of time. However, the dynamics of recently eroded sediments from the landslide bare slope are poorly understood. This study initially verifies the accuracy of the terrain model derived from Unmanned Aerial Vehicle-Structure from Motion (UAV-SfM) survey on the landslide bare slope by comparing it with the topographic model derived from a Terrestrial Laser Scanning (TLS) survey. The UAV-SfM survey derived a terrain model with a high resolution of approximately 10 cm. Further, due to the effects of 2018 Hokkaido Eastern Iburi Earthquake, sediment dynamics on the landslide bare slope was analyzed for two consecutive years at frequency of every 3 months using UAV-SfM survey. Immediately after the earthquake, unstable materials on slope collapsed. Subsequently, the sediment dynamics exhibited seasonal fluctuations. Snow glide and rock slaking caused surface erosion of sediments during the winter. In the snowmelt season, gully erosion occurred due to snowmelt flooding. The eroded sediments formed talus cones at the foot of the slopes. In the summer (the first year after the earthquake), gully erosion occurred not only on the bare landslide slope but also on the talus cones due to the surface flow of rainfall. During the winter and snowmelt season (the second time after the earthquake), surface and gully erosion occurred again on the lower side slope, whereas gullies on the talus cones were filled with debris supplied from the bare slope. In consequence, however, the gully erosion of the talus cones occurred by the rainfall. This implies that the eroded sediments on the landslide bare slope are discharged downstream during the snowmelt period with a time gap. Thus, this study provides an in-depth understanding of sediment dynamics on landslides caused due to an earthquake, using multi-temporal UAV-SfM survey.

Sediment movement in mountain areas is often induced by heavy rainfall. Hence, rainfall observation in mountain areas is crucially important for prevention of sediment-related disasters. Although rainfall is measured with tipping bucket rain gauges and weather radar all over Japan, we have a technical challenge in respect of spatio-temporal resolution for the observation network. Therefore, we attempt to develop a novel method for estimating rainfall intensity at a high spatio-temporal resolution with closed-circuit television (CCTV) surveillance cameras. We collected videos of three CCTV cameras during rainfall events and acquired digital image data from those videos at the one-minute interval. Previous analyses showed that the contrast and color of images are drastically affected or degraded under rainfall conditions. Based on the results of these analyses, we analyzed the relationships between rainfall intensity and pixel values. Results show that the pixel values go higher and frequency distributions of pixel values become narrower with increasing rainfall. Moreover, the introduced pixel value indices which are means of pixel values in analytical patches on images fluctuate in response to rainfall in time series. The results indicate that the indices are applicable to observe the change of rainfall intensity. We also showed that place and size of analytical patches on images is important for this analysis. Based on these results, we estimated fluctuations of the rainfall intensity from the fluctuation of the index at one-minute interval. Consequently, we will be able to better estimate amounts of rainfall at a high spatio-temporal resolution in mountain area by utilizing the current operational CCTV camera network.

The Basic Guidelines for Sediment Disaster Prevention are established by the Minister of Land, Infrastructure, Transport and Tourism under Article 3 of Sediment Disaster Prevention Act (Act No. 57 of 2000). Since its initial establishment in 2001, the Basic Guidelines have undergone successive revisions to deal with problems identified in major sediment disasters that occurred in this century. Now the Basic Guidelines clarify nature of sediment disaster and principles of its prevention, and detail wide variety of prevention measures under the Act. They include precautionary measures such as planning of warning and evacuation system, and emergency operational measures such as orientation and support of evacuation behavior. Some of the provisions of the Basic Guidelines are not positively delegated by the Act, but no less important. The Basic Guidelines play a central role in sediment disaster prevention policy in Japan and their importance will not cease to grow in the climate-change era.

An open-type steel Sabo dam is mainly constructed as a protective structure on debris flow. In load bearing capacity evaluation, despite the difference of trapping mechanism, design manual of an open-type steel Sabo dam is utilizing the design concept of a closed-type Sabo dam. However, the effect of structural permeability on the debris flow load is unclear from viewpoint of dynamic debris flow load. This study experimentally evaluates the effect of structural permeability of open-type steel Sabo dam as a dynamic debris flow load. The experiment focuses on overturn limit state by using an experimental device can rotate when debris flow exceeds at the failure limit. Difference of a dynamic debris flow load distribution between an open-type and a closed-Sabo dam model under same conditions was revealed. Also, moment load on closed-type Sabo dam is larger than that on the open-type one.