2016年北海道豪雨災害で常呂川・十勝川流域で発生した河川災害

Abstract

Field survey on the flood and sediment disaster which was happen in Tokachi and Tokoro River Basins in Hokkaido in 2016 is performed and the characteristics of the disaster is discussed focusing on levee break phenomena and disasters around bridges. Population density around rivers is low in Hokkaido. Hence, river width between right and left levees is very wide, even though flood discharge is small. As a result, long bridges over rivers from right levee to left one have not been constructed. On the other hand, short bridges over only main channel and connecting roads between levee and bridge are constructed. The connecting roads between levee and bridge decrease the river cross-section and increases the flood risk. Furthermore, land elevation on the floodplain tends to be lower than the river bed elevation in Hokkaido. As a result, the levee breaks without inundation phenomena was happen in Satsunai River. Additionally, flood water tends to return to rivers soon due to the high elevation of floodplain.