Damage to the diagonal bracing of a steel pipe Sabo dam due to overflow boulders, or debris flow has been reported at the 5^th Sabo dam on the Omu River after the dam reaches full sand deposition. The cause of damaged steel members remains uncertain. This study examines damage factors of the dams by overflow boulders with Distinct Element Method. The analysis parameters are based on datum from disaster investigations. A flow velocity distribution model is constructed from preliminary experiments. Following the disaster, boulder size, velocity, and water depth were determined through field surveys to evaluate potential damage to steel members of the dams. Findings reveal that the initial damage was caused by 5.0 m boulder collisions, followed by 1.0―2.0 m boulders, which continued to cause significant damage. This phenomenon led to simultaneous downstream flow of accumulated boulders at the dam's top, resulting in damage to both diagonal and horizontal bracing of the dam.

It has been noted the “immunity of landslides”, which means landslides are less likely to occur on landslide experienced slopes, but it has not yet been clarified. To reveal the immunity of landslides, the spatial distribution and characteristics of shallow landslides caused by heavy rainfall in 1967 and 2022 in the Murakami City, Niigata Prefecture were analyzed. The results showed that only 20% of the 2022 landslides overlapped with the 1967 landslides. The soil in the 1967 landslides area had developed only about 10 cm in 55 years, which is insufficient to destabilize the slopes and cause new landslides. The 2022 landslides occurred on landslide-prone slopes that did not experience landslides due to heavy rainfall in 1967. These results indicate that the immunity of landslide is exerted at least for 55 years on the landslide occurred point. However, if areas with high potential for landslide occurrences remain within a watershed, immunity of landslide at the watershed scale is not expected.

Debris flows, historically termed Mountain tsunamis commencing, are common hazards in Japan. More recently, a comprehensive description of a destructive debris flow in Atami City, that includes photographs and video records has been published. This heightened societal awareness and created demand for in-depth evaluation of the efficacies of countermeasures, such as sabo dams. This study introduces a system in which topographic data collated using BIM/CIM are linked to contemporary user interfaces such as metaverse, and numerical simulations are employed to assess the efficacies against debris flow, and to develop informative materials for local community meetings. We conducted a survey among the general populace to ascertain the validity and necessity of our proposed four-dimensional video material. Approximately two-thirds of the responses indicated a perceived usefulness and necessity for such material.

In this study, we analyzed the long-term reanalysis data set JRA-55 using the WRF regional meteorological model for the heavy rain that caused a large-scale landslide disaster in the upper Tenryu River basin in June 1961. The heavy rainfall of June 1961 was reproduced with a temporal resolution of 1 hour and a horizontal resolution of 1 km. The simulation results were analyzed by comparing the calculated results with the ground rain gauge observations. This is the first attempt in the literature to analyze the cause of heavy rain in the era when there were no radar rain gauges. The detailed rainfall distribution of the upper Tenryu River basin has been reproduced. From the reproduction results, we found the cause of the torrential rain. It was found that the cause of the heavy rains in areas where landslides were severe was convergence field to the strong influence of independent peaks and narrow topography in the upper reaches of the Tenryu River, and convergence field strengthened rainfall. This work was derived from the WRF model using universal equations. For this reason, it is possible that the results obtained in this research are also valid for other torrential rains. It is expected that the results of this research will be useful for future disaster prevention and erosion control plans.

For beaches, the wind-blown sand may need to be controlled in the region from the shoreline to the landward end of the dry beach to prevent sand transport by the wind from the beach surface, eroded, and subsequently deposited in unwanted areas. It was necessary to develop integrated countermeasures against windblown sand dispersal on the limited width of the beach nourishment. Therefore, a literature review was conducted focusing on effective measures to control windblown sand dispersal. The results showed that sand fences, sand trap trenches, beach earthworks, and vegetation are effective measures to control windblown sand on the beach. Sand fences, sand trapping trenches, and vegetation were selected as control devices to stop and stabilize blown sand generated in the seaward region of the beach. Then, a series of field experiments were conducted to examine the function of sand fences, trenches, vegetation, and combinations of these structures. The field experiments yielded the following results. 1) Sand fences functioned well if the sediment was removed before about 70% of its height was filled, 2) Two different sand fence arrangements were tested on a natural beach, which are a configuration that combines a straight line and a transverse alignment, and a configuration that combines a straight line and a perpendicular alignment. The former configuration was functionally superior, but the latter also worked well. 3) A rectangular trench with 1 m deep and 5 m wide also functioned well until the trench was filled. 4) Vegetation work with sand grasses did not trap as much blown sand as expected. 5) A combination of structures, vegetation, trench, and sand fences positioned from the shoreline was found to be effective in controlling blown sand.