安倍川中流・蕨野地区の西側山腹崩壊で生じた河道閉塞と1914年の水害

抄録

The Abe River is one of the steepest rivers in Japan (channel length 51 km, drainage area 567 km²), originating from Oya Peak (elev. 1999.7 m) running through the central area of Shizuoka City. Several severe floods occurred in this river, including the floods of 1828 and 1914. When the typhoon struck on Aug. 28, 1914, the upstream area of the Abe River was subject to rainfall of more than 400 mm. This caused a major flood over Shizuoka City area, resulting in severe damage including 45 death, 1,000 houses washed away, and 10,000 houses inundated. It was found that the cause of this flood was not only the heavy rainfall but also river-bet blockage at 23.5 km from the river mouth. This blockage, caused by the large-scale landside (200 m wide, 180 m high) on the right bank, covered more than 2/3 of the river width (500 m) and created a landslide dam with a height 15 m, area 320,000 m², and volume 1,600,000 m³. This landslide dam burst immediately, triggering a flood surge which attacked the city area downstream. We can see well that the topography of this area has changed over the years if we examine 1/5000 to 1/50,000 scale topographical maps prepared by Geographical Survey Institute in 1889, 1896, 1916, 1948, 1974, and 1978 (including corrective surveys).