Author(s): Tomoko Kyuka; Yasuyuki Shimizu; Kazunori Okabe; Kho Shinjo; Satomi Yamaguchi
Linked Author(s): Yasuyuki Shimizu, Tomoko Kyuka
Keywords: Channel migration; Meandering; Bank erosion; Unsteady discharge; Otofuke River
Abstract: The Otofuke River is a tributary of the Tokachi River, Hokkaido Japan, having steep slope and a wide designed width. In 2016 August, the river witnessed four major flooding events with a record breaking discharge, within a time span of as short as 14 days. Otofuke River has a single thread straight channel. However, due to the frequent flooding, the river promptly followed a sinusoidal path damaging the river bank embankments. The straight channel of Otofuke River faced active erosion of the banks leading into a significant migration in the path of the channel. This also led to damage of bank embankments and levee breaches at the seven locations. In order to understand the mechanism of river embankment destruction, it is important to know the complex interaction between rapid channel migration and sediment. Also, it is inevitably crucial to understand the effect of unsteady discharge. Results from field survey, the rapid formation of sine curves in Otofuke River was presented after the last typhoon by aerial photographs. Moreover, according to the maximum water level traces, the bank erosions were considered to develop after the peak discharge. Numerical analysis explained that sediment accumulation becomes active as flow rate decreases, and its strongly deflect the flow path transversely, embankment direction. This phenomenon would swift a channel formation of meandering and alternate bars.
Year: 2018