Author(s): Takuya Inoue; Tamaki Sumner; Kazuo Kato; Hiroki Yabe; Yasuyuki Shimizu
Linked Author(s): Yasuyuki Shimizu
Keywords: Bank erosion; Bridge collapse; Sediment supply; Field observation; Numerical simulation
Abstract: In Hokkaido (Japan), 4 typhoons caused widespread flooding, landslides and collapsing bridges during August 2016. Many of collapsed bridges were located near apex of alluvial fans, and large volumes of sediments were deposited. In this study, we performed field observations of 4 collapsed bridges and numerical simulations to investigate the effects of sediment supply on bridge collapses. Our observation results indicated that large river-bank erosion caused collapsing of the bridge abutment that set on the river bank. The numerical results showed that: (1) bank erosion width basically increases with increasing volumetric flow rate (discharge). In the same discharge, the bank erosion width greatly differs depending on the conditions of sediment supply. When the sediment supply is large, an alluvial point bar forms and develops. The point bar pushes the river flow against the outside bank of the bend, and promotes bank erosion. In contrast, small volume of sediment supply suppresses river bank erosion and evokes river bed erosion instead; (2) Furthermore, river bank erosion also depends on changes in water discharge, the bank erosion width increases during the recession limb rather than during the rising limb. This is because sediments deposits in the recession limb promote the development of the alluvial point bar.
Year: 2018