“Kanto-Tohoku heavy rainfall disaster on September 2015” due to an unprecedented rainfall on September 9th through 10th caused serious damage such as embankment collapse in Kinugawa River basin. Four MLIT dams in the upstream area of Kinugawa River (Ikari, Kawamata, Kawaji and Yunishigawa) contributed greatly to the flood damage reduction by implementing operations using the flood control capacity as much as possible and reducing outflow from the dams considering downstream water level and damage. The total amount stored in the dams was about 100 million m³.

When constructing a trapezoidal dam with cemented sand and gravel, it is standard practice to produce embankment material by mixing locally available earth material such as riverbed deposits and excavated material with cement and water. In order to achieve the required strength of embankment material, therefore, grading control checks need to be made to ensure that its strength is kept within the allowable range. The conventional practice is to take samples and carry out sieve analyses at regular intervals, which is both labor- and time-consuming. The authors have developed a new continuous grading management system using three-dimensional image processing technology. The newly developed system makes real-time monitoring of grading possible by irradiating line laser light onto the material on the conveyor, calculating the volume of particles of each size from the image data continuously acquired with a digital camera and thereby determining particle size distribution.

Mt. Ontake erupted on September 27, 2014 and it was the second time in recorded history. The distribution and volume of products by the volcanic eruption were almost similar to those of the previous in 1979. Therefore, the influence of the eruption on the water quality of Makio Dam reservoir, where Mt. Ontake is located in its catchment, was estimated to continue over a long period. In response to this situation, Japan Water Agency (JWA) has collaborated with local governments concerned and water users to implement not only efficient water quality monitoring but also appropriate measures for water quality conservation while making accurate forecast of discharged turbidity. As a result, the dam has kept supplying water to the downstream continuously without any particular trouble in water use.

The shear friction factor of safety of concrete gravity dams is reviewed historically. The existing shear friction factor of safety is evaluated theoretically and the further improving method of the factor is discussed. The new evaluation equation is proposed.