Log boom is installed in dam reservoirs to prevent gate blockages and driftwood run-off. If the aging log boom is damaged and the driftwood trapping function is impaired, this will be a significant problem for dam safety management. However, the degradation mechanism still needs to be fully clarified. Therefore, in this study, field surveys and laboratory experiments were conducted to clarify the age-related deterioration mechanism of the net section. The results showed that the log boom was degraded by ultraviolet rays, driftwood contact, and contact with slopes and that the degradation factors differed according to the log boom arrangement. The probability of net breakage due to degradation was assumed to vary with the magnitude of the external force, and a method was proposed to determine the time when the net starts to break, taking into account the net degradation measures against abrasion and the assumed external force on the log boom area.

In this study, in order to analyze the relationship between the reasons for the visiting that are listed in the national survey on natural environment in river and watershore (hereafter, the survey) and the potential tourism trends, we evaluated the tourism trends to the dams by using human flow data and social sensing such as Twitter and Google Trends. As the result, it was found that the reasons for visiting the dams listed in the survey and the activities of dam invitations such as the dam card and dam curry appeared in the Twitter data. In addition, it is shown that the potential reasons for visiting that are not listed in the survey could be evaluated by the evaluation of the characteristics such as the effect of tourism by a popular cartoon, surrounding facilities and the events around the dams with combined analysis of the Twitter and Google Trends.

An attempt for identifying the complex hydrogeological structure of rock foundation for fill dam by installing the pore water pressure gauge in rock layer, measuring its behavior during artificial change of underground water level with support of FEM analysis is reported. For evaluating the quality of curtain grouting and its in-situ impermeability before test reserving using installed pore water pressure gauge, ICT grouting site quality control system enabling the three-dimensional visualization including the relationship between pore water pressure behavior and grouting execution history is also introduced.

Sediment volume surveying is mandatory for many dam reservoirs and is an essential source of information for safe and sustainable dam operation. In recent years, the emergence of multibeam echo sounders (MBES) has made it possible to survey bathymetry with much higher accuracy than in the past. On the other hand, errors are inevitable in bathymetric surveying, which sometimes manifests as a problem of “negative sedimentation,” a decrease in the amount of sediment in the data compared to the previous period. This study introduces the factors that cause errors in acoustic bathymetry, including MBES. In addition, we analyze 20 years of acoustic bathymetry data obtained at the Murou Dam, Japan, and show that errors frequently occur in the reservoir-sloped areas.

This report describes the results of an environmental monitoring study and the development of a sediment supply test downstream of a multi-purpose dam located in the Yoro River, Chiba Prefecture, which is a sand-bed river, that has been conducted for about 10 years. The annual sediment supply volume was increased from 1,500 m³ to 10,000 m³ by reviewing the timing, frequency, shape, etc. of sediment placement in the river channel. In monitoring surveys, various surveys were continuously conducted in the downstream river, and no particular impact was observed. On the other hand, it was confirmed that the proportion of fish species that prefer sand beds tended to increase with the expansion of the distribution range of sand content.

Seismic wave velocities in the embankment of Naramata Dam in Gunma prefecture, Japan, operated by the Japan Water Agency and the vibration characteristics of the embankment were examined. The results revealed that (1) the estimated S-wave velocities were respectively 350-360 m/s and 540-570 m/s in the upper and the lower sections of the core zone, and (2) those in rock zones were 560-600 m/s in both the upstream and downstream side, and a polarity anisotropy of the S-wave velocities was seen. (3) The P-wave velocities were 520 m/s in the upper section and 1,950 m/s in the lower section of the core zone and (4) 1,800 m/s in the upstream side and 1,100 m/s in the downstream side of the rock zones, and this difference is attributed to the saturation of soils due to the reservoir water. (5) The natural frequency of the embankment evaluated by FE-BE analysis based on the abovementioned soil properties was identical with that obtained from observed spectrum ratios.