Outbursts and disasters of Takaisoyama and Hose Landslide dams (1892) in East Shikoku

Abstract

Takaisoyama and Hose landslides occurred by heavy rainfall of typhoon in 25 July, 1892, in east Shikoku. These landslides blocked rivers and formed landslide dams. Many old documents illustrated outbursts and disasters of Takai-soyama and Hose Landslide dams. Takaisoyama landslide blocked Naka River and formed landslide dam of 71 m in height and 7.25×10⁷ m³ in volume (Terado, 1970). The landslide dam broke down when the dam lake was filled with water after 1.87×10⁵ seconds ( 52 hours), and the big flood rushed down the valley of Naka River, with the damage of more than 300 houses and the victims of 60 persons. Calculating by Manning formula, the peak flood discharge started by velocity of 10-12 m /second(average velocity of 5 m /second)and a volume of 3.0×10⁴ m³/second, and rushed down by 3 hours at the distance of 49.3 km from the landslide dam. This flood reached by 7.5 hours at the distance of 72km in the estuary of Naka River. Hose Landslide blocked Kaifu River and formed landslide dam of 80 m in height and 3.3×10⁷ m³ in volume. The landslide dam broke down after 1.08×10⁵ seconds (30 hours) or 1.94 ×10⁵ seconds (54 hours), and the big flood rushed down the valley of Kaifu River with the damage of more than 20 houses and the victims of 47 persons. This flood rushed down in 3-4 hours at the distance of 23 km in the estuary of Kaifu River.