In this study, we propose an empirical method for the probabilistic prediction of travel distance from landslide areas in an earthquake-induced landslide and then verify the applicability of the proposed method. In order to propose a probabilistic prediction method, we analyze the relationship between the travel distance (L) and landslide areas (A) in cases of landslides triggered by the Niigata-Chuetsu earthquake, the Iwate-Miyagi Nairiku earthquake, and the 2016 Kumamoto earthquake. We found that there was a power-law relationship between the measured travel distance and landslide area. This suggests that the travel distance might be predicted using the landslide area. However, the travel distances were largely scattered. Therefore, we propose a formula that can predict the probability of travel distance using F(r), which is the cumulative distribution function of the normal distribution of the ratio of the predicted and measured travel distance, Ri, since we find that it shows normal distribution in our three cases. In order to verify the proposed formula, we prepared training and test datasets for each case of the three earthquakes. Further we verified how much the probability of the travel distance in test datasets could be described by the proposed method.

Sediment-related disasters (hereby SRD in this study) are triggered by inciting causes as heavy rain and earthquakes where lands are affected by primary factors as steep topography and geological conditions. Much study has been conducted on primary factors so far. The results, however, are not fully applied to disaster mitigation measures such as alerts and warnings due, in part, to overwhelming amounts of studies and their apparent inconsistency. Related suitable theme maps are handful if coverage of the entire national land is taken into account. Principal candidates among these are : landslide distribution maps based on air photo analysis by the National Institute of Disaster Prevention Science and Technology, SRD warning zone maps, and deep-seated failure frequency maps by Sabo administration of the Ministry of Land, Infrastructure, Transport and Tourism. These maps are digitized, but not rasterized to be used readily via geographical information systems. We have rasterized these maps in a common way. 24-year SRD records administered by Sabo administration are used to examine the quality of rasterization and data matching. The data matching shows that SRD warning zone maps are most fitted to general SRDs with hit rates of 7.36%, 3 times higher than when primary causes are ignored completely, and missed rates of 10.91%. On the other hand, deep-seated failure frequency maps combined with landslide distribution maps are most fitted to large-scale sediment-related disasters have 0.36% and 68.93% respectively. The results indicate that primary factors reflected to theme maps, even with coarse 1-km spatial resolution, can provide useful information for disaster prevention. The rasterization method proposed in this study, when applied cautiously, is regarded conductive to bring parts of past studies into practices.

Predicting sediment discharge volumes from mountain catchments is one of key issues to assess damage induced by sediment laden flood. We evaluated sediment discharge volumes from mountain watersheds due to the sediment disaster July 2017 in Northern Kyushu using LiDAR data and rainfall data having a high in time and space resolution. Specific sediment discharge volumes from first-order catchments were highly varied by two order of magnitude despite no obvious differences in rainfall condition and relief of catchment. Fifteen to twenty five percent of first order catchments discharged larger than 500% or smaller than 20% of median specific sediment discharge volumes. Averaged specific sediment discharge volumes from second or third order catchments were almost the same as first order catchment.

However, spatial variability of specific discharge was dramatically decreased with increase of stream order. These patterns were probably due to mixing of randomly distributed sediment discharge in first-order catchment.

Main pillars of non-structural measures against sediment related disasters in France are ; 1) Information sharing of risks of sediment related disasters 2) Natural disasters prevention plan established by governors (préfets) for municipalities. The plan provides zonings identifying nature and extent of natural disaster risks that each zone faces. It stipulates legally binding land use regulations for each zone as well as protection and safeguard measures to be taken by municipalities or property owners as appropriate. The regulations and measures are expected to correspond to the risks identified in the zoning. 3) Natural disasters casualty insurance automatically attached to ordinary property insurances. It covers damages causes by major natural disasters recognized as such by relevant ministers. A fixed portion of its premium revenue is earmarked for government-run fund. The fund gives financial assistance for the protection and safeguard measures under the natural disasters prevention plan. It also finances takings or purchases of properties representing grave risks of human lives due to natural disasters.

Distance measurement by Total Station (TS) is often used in long-range monitoring for slope displacement. Assuming the vertical displacement can be ignored, distance measurements in two directions allow to calculate surface displacement vectors. However, it is unclear if the assumption is appropriate. In this study, the authors derived mathematical model representing the relation between 3-dimentional vector of surface displacement and distance changes of two-direction, and then examined the impact of the assumption of vertical component for calculating horizontal component by a case study of TS measurement in Mt. Unzen-Fugen-Dake. The results showed that calculated horizontal displacement could change up to 78 degrees in direction and 0.34 times in magnitude following the change of assumed vertical displacement in possible range. It was identified that the vertical displacement cannot be ignored easily. Furthermore, the authors proposed a method to estimate each component of 3-dimention, using supplemental data from LiDAR. Three-dimensional vector is likely to be estimated within a certain level of accuracy under the following conditions : (1) when the angle between two observation directions is larger than 25 degrees, and (2) when the angle between each observation direction of two TSs and estimated moving direction is smaller than 75 degrees.

The northern Kyushu heavy rain in July 2017 caused many sediment disasters in a wide area and devastating damages. Although various sediment movement phenomena such as collapse and debris flow may have occurred in a basin due to prolonged high-intensity rainfall, the actual situation has not been grasped. In this study, we assumed the time and spatial distribution of locations of sediment transport phenomena and evacuation based on a questionnaire survey conducted in the Akatani River basin, Asakura City, Fukuoka Prefecture, where severe damage was caused by the heavy rainfall. During this disaster, 57% of the residents, who were near Asakura city on July 5, evacuated, 35% did not evacuate, and 8% could not evacuate. 41% of the evacuees evacuated on their own or rescued after receiving some damage. Evacuation types were classified into three types based on the relationship between the time change of sediment transport and evacuation start time. Because many evacuees started during the period when sediment movement was active, the necessity of evacuation measures on the premise of imminent evacuation was identified as an issue in addition to evacuation before sediment movement occurred.

A debris flow along with driftwood occurred on September 10, 2015 in the Tamosawa watershed. The open type steel sabo dam named “Tamosawa Dai-ichi” protected houses against the debris flow by trapping sediments and driftwood. We investigated the amount and the structure of the sediments and driftwood captured by the dam during the excavation work at the sedimentation area. In this paper, we reported the survey method of the captured sediments and driftwood, the estimated sediment transport characteristics from the investigation, the results of blockage condition of the opening part of the dam capturing debris flow mixed with driftwood, and the volume ratio of the captured driftwood to the planned total amount of out-flow to the downstream.