Emergency Responses to Debris Flow Disaster at Serizawa District, Nikko City Triggered by the 2015 Torrential Rains in the Kanto and Tohoku Region

Kenji MIWA and Kenji TAKETOSHI

In September 2015, torrential rain hit the Kanto and Tohoku regions causing debris flow in seven mountain streams in the Serizawa District of Nikko City, Tochigi Prefecture, where the greatest rainfall was observed in recorded history. As a result seven houses were completely or partially destroyed and the municipal road was cut off by sediment runoff from the mountain streams. River bed aggradation and swelling of the main Serizawa River eroded river banks and partly washed away the municipal road. As a result, 25 inhabitants from 14 households were temporarily isolated in an upstream village. The Nikko Sabo Office of the Ministry of Land, Infrastructure, Transport and Tourism, immediately began to investigate the damage caused in the Serizawa District. Based on the results of the investigation we first made emergency repairs to the road followed by construction of temporary water channels to divert the water flow from the mountain streams. As the next step, we set up monitoring equipment and created a system to alert vehicles and people traveling on the road of the impending dangers. With these efforts we were able to ensure immediate safety until more permanent measures were constructed.

2018/1 153-162