A new method estimating sediment discharge using the pipe hydrophone pulses obtained with multiple amplification factors was proposed. In the method, the proportions of sediment that does not collide with the pipe due to salutation and sediment below the detection limit of grain size by the hydrophone are considered. With this method, it is possible to estimate not only the sediment discharge but also the grain size distribution partially. To verify the validity, the simulated sediment discharge and particle size distribution are compared with the observed values. As a result, the new estimation method simulates the observed sediment discharge and grain size distribution reasonably. However, it was shown that the estimation accuracy varied depending on the individual sediment transport events and the ratio of sediment above the detection limit grain size α_n,us plays important role. In addition, sediment discharge simulated by the new method was compared with the conventional pulse method. The result indicates that the new method was not always more accurate than the conventional pulse method for individual events. However, while the conventional method has a large variation between events, the new method can stably maintain high accuracy, and it is shown that the average value for the entire period is superior to the conventional method. It was also found that the value of αdetermined from the grain size distribution needs to be set appropriately to improve the accuracy by this method. In the future, it is a potential solution to measure the grain size distribution in a short period of time. Or, to reduce the dependence on α , it is necessary to widen the range of the amplification factor that can be used in the estimation method. For that purpose, the detection rate that changes due to pulse saturation should be quantified.

Studies of countermeasures against sediment-related disasters often focus on structural measures; however, nonstructural measures, including warning and evacuation, also play important roles in protecting human lives. Such nonstructural measures were enacted in Japan in 2001; however, since human responses to sediment-related disasters are influenced by many factors, the effects of these measures are typically studied in terms of a small number of individual cases, and remain poorly understood. Therefore, in this study, we conducted in-person interviews and questionnaire surveys to examine the effects of non-structural measures implemented before disasters occurred in five municipalities of Nagano Prefecture, where Typhoon Hagibis caused sediment-related disasters with no human injury or loss of life. The survey results indicate that co-operation and information exchange within and outside the regional unit were required for effective warning and evacuation actions in each regional unit. Therefore, we scored the measures in terms of their effects on information provision and communication opportunities. As the scores of these effects increased, the evacuation rates during disasters increased, although sex differences among regional units may have had an influence. In areas that had experienced severe property damage following sediment-related disasters, evacuation rates were found to be related only to communication opportunities. To improve the effects of non-structural sediment-related disaster countermeasures, we propose that the numbers of disaster prevention drills and seminars should be increased, and that more organisations should be involved in their implementation, ensuring the use of a wider range of methods. Furthermore, showing the importance of communication opportunities provided by incorporating non-structural measures into law would also be effective for preventing human losses.

Predicting occurrences of landslides or debris flows at a specific slope is critical for early warning. Instead of the groundwater height, discharge of a spring at a slope adjacent to a primary school was observed and simulated by a functional model, which includes long- and short-term precipitation terms. The long-term precipitation term was determined by fitting the observed spring discharge, whereas the short-term precipitation term was determined so that the model yields significantly large spring discharges during recent disasters in the district. The comparison between the observed and calculated discharge showed 0.8 of the Nash-Sutcliffe efficiency factor. The simulation of the spring discharge from 1976 to 2020 revealed that the calculated discharges during the recent disasters were within the greatest 0.1% of the entire period. These results suggest the robustness of our simple functional model and less failure of the disaster prediction.