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Flood Inundation Modelling Considering the Effect of Debris Blockage in Bridges

Author(s): M. A. C. Niroshinie; Yasuo Nihei

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Keywords: Coupled 1d-2d models; Flood inundation; Water level profile; Woody debris

Abstract: Nowadays, flooding is quite frequent natural disaster in many countries. The frequency of flooding has increased due to various issues including the impacts of the climate change. Wood debris can increase the significance of flooding simply by increasing the destructive power of the floods. Yoshino River in Yamagata prefecture, Japan is a tributary of Mogami River which flows through mountainous areas covered with forests. During a typhoon in 2014, Yoshino River overflowed and flooded the surrounding areas causing significant damages to the residents in Akayu area. The main cause of this flood has been identified as the blockages by woody debris at bridge piers along the river. This paper discusses a study of a numerical simulation of this flooding along with the field measurements. A coupled 1D and 2D numerical model was prepared in this study. The effects of blockages at bridge piers by woody debris were simulated in the model by increasing the Manning’s roughness at the bridge piers. The pattern of debris blockage and its effects were obtained from a laboratory experiment. The prepared model was verified using the field measurements of water level at Hanamibashi bridge and the maximum water levels along the river. The verified model was then used to analysis the effects of debris on the overflow depths and discharges. The results indicate that river overflowed at some bridges due to the blockages by debris. In addition, it was also observed that the overflows have been resulted not only by the blockages but also due to low elevation of the river levees.


Year: 2016

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