Wataru SAKURAI, Ryo SAKAI, Yuuki OKUYAMA, Takahisa MIZUYAMA, Akihiko IKEDA, Soichi KAIHARA, Noriko TADAKUMA, Yoshiaki KASHIWABARA, Kosuke YOSHINO, Yoshito OGAWAUCHI, Hidetomo TATSUMI and Toru SHIMADA
During Typhoon No. 12 (Talas, September 2011), large landslide dams formed as a result of a deep]seated landslide in Kii Peninsula. Subsequently, Kii Mountain District Sabo Office, Ministry of Land Infrastructure, Transport, and Tourism, developed countermeasures. However, frequent debris discharges from the slope of the deep]seated landslide and severe erosion on the landslide dams has hindered progress on the countermeasure works. On 10 August 2014, during Typhoon No. 11 (Halong), in which the greatest rainfall observed since Typhoon No. 12 of 2012 occurred, a large re]slide with an estimated collapsed soil volume of 760,000m3 increased the height of Akadani Landslide Dam in the area of Gojo city, Nara Prefecture. Subsequently, large sediment discharge was caused by severe erosion on the landslide dam due to overflow from the dam lake. At Kuridaira Landslide Dam, with a height reaching 100m, in Totsukawa village, Nara Prefecture, overflow from the dam lake caused severe erosion of the landslide dam and large sediment discharge with an estimated volume of 1,600,000m3, which destroyed countermeasure facilities. Although the countermeasures were disturbed by Typhoon No. 11, the effects of the countermeasure facilities such as sabo dam were confirmed. Therefore, we clarified the processes of the large]scale erosion and sediment discharge affecting the landslide dam and verified the effects of countermeasure facilities, countermeasure principles, and the countermeasure plan. Furthermore, we suggested a practical method to mitigate the damage caused by large]scale erosion of, and sediment discharge from, a landslide dam that occurs before completion of the entire countermeasures.
Key wordsFlandslide dam, dam erosion, sediment discharge, countermeasures