## (ix) Issuing Sediment Disaster Alert

In case that the risk of sediment-related disasters increases due to heavy rainfall, Sediment Disaster Alert is jointly issued by prefectures and the Japan Meteorological Agency over the respective-municipalities. Issuance of the Sediment Disaster Alert is expected to lead issuance of evacuation orders announced by the municipalities and/or self-evacuation of residents. In order to support such operation, the Agency also provides detailed mesh-data indicating the risk of sediment-related disasters as well as detailed precipitation data.

Figure II-7-2-9

Sediment Disaster Alert, and Risk of Sediment Disaster and “High-resolution Precipitation Nowcasts”

Source) Japan Meteorological Agency

## (3) Volcanic Disaster Countermeasures

## (i) Countermeasures for Sediment-related Disasters Following Volcanic Activity

In preparation for the volcanic mudflow caused by volcanic eruptions and the debris flow caused by rainfall, sediment control dams, training dikes, and so on for preventing or reducing damage are being constructed. In addition, for facilities that are unable to properly maintain their functions due to continued and massive debris flow, removing sediment deposition and other measures are being carried out to keep effectiveness.

Sediment-related disasters following volcanic eruptions could lead to large-scale disasters. In addition, it is very difficult to predict the position or scale of the eruption with good accuracy beforehand, causing serious damage. For this reason, a sediment-control plan for the emergency mitigation of the effects of a volcanic eruption is being formulated in order to mitigate damage through agile responses to volcanic conditions in combination with

Figure II-7-2-10

Development of volcano hazard maps, formulation of volcanic eruption emergency disaster-mitigation measures and sediment-control plans, and the state of the operations of eruption warning levels for fifty volcanoes that have been selected by the Coordinating Committee for the Prediction of Volcanic Eruptions as volcanoes requiring an upgraded system of monitoring and observations for the prevention of volcanic disasters

the development of facilities in advance; this plan targets forty-nine volcanoes that exhibit active volcanic activity and that are at risk of causing sediment-related disasters in the wake of an eruption. The amended Active Volcanoes Act came into force in December 2015 and prefectural governments, Regional Development Bureaus, and other sediment-control departments, as members of the Volcanic Disaster-Prevention Council, decided that they would study volcano hazard maps from the standpoint of sediment-related disasters caused by eruptions. Thus, by developing volcanic sediment-control hazard maps (volcanic hazard maps that relate to sediment-related disasters), support was provided for a series of studies on alerts and evacuation systems by the Volcanic Disaster-Prevention Council.

In response to the eruption of Kuchinoerabujima in May 2015, a survey of conditions conducted by helicopter revealed that small debris flows were being generated in Mukaehama River; relevant information was provided to the relevant local authorities. Surveys have also been conducted to ascertain local conditions, such as in terms of ash fall deposit, in and around Asosan (Mt. Aso), Hakoneyama (Mt. Hakone), Asamayama (Mt. Asama), and other such volcanoes that either