The Effects of Hydraulic Structures on Streams Prone to Bank Erosion in an Intense Flood Event: A Case Study from Eastern Hokkaido

Daisuke AOKI, Mio KASAI and Mari IGURA

Bank erosion can induce huge financial damage by eroding lands and destroying properties and infrastructures along the river. Understanding the process is first necessary so that hydraulic structures could be placed efficiently to prevent disasters. This study examined the process during an intense storm in August 2016 in Pekerebetsu and Kobayashi Rivers, the eastern Hokkaido Island in Japan, which caused disastrous damage in the area. The analyses of airborne LiDAR data, satellite imagery, and field survey revealed that debris flows produced from weathered granites in the headwaters triggered drastic channel widening by eroding banks consisted of incoherent periglacial colluviums in the upstream reaches. Sediment produced there deposited in the next gentler downstream reach (< 2 degrees), naturally in Kobayashi River, and by a dam in Perekebetsu River. For the former reduction in the amount of sediment transported limited bank erosion in the further downstream. In contrast, for the latter flow travelled encouraged vertical and then lateral erosion at the outlet of a reach containing a gorge and groundsills. Sediment produced from there aggraded beds in the further downstream to cause more bank erosion in turn. The results suggested that change in hydraulic condition created by valley configuration or hydraulic structures should be first understood for efficient and effective disaster prevention planning not only at a reach scale but also a catchment scale.

2018/1 270-275