Development of a meandering channel caused by the planform shape of the river bank

T Nagata,H Yasuda,Y Watanabe,A Ito

doi:10.5194/esurf-2-255-2014

Abstract

Abstract. Due to a typhoon and a stationary rain front, record amounts of rain fell in September 2011, and the largest class of discharge in recorded history was observed in the Otofuke River of eastern Hokkaido in Japan, and extensive bank erosion occurred in various parts of the river channel. Damages were especially serious in the middle reaches, where part of a dike was washed out. The results of a post-flood survey suggested that the direct cause of the dike breach was lateral advance of the bank erosion associated with the development of meandering channels. As the related development mechanism and predominant factors have not yet been clarified, this remains a priority from the viewpoint of disaster prevention. A past study on the development of meandering channels was reported by Shimizu et al. (1996). In this study, the meandering channel development process was reproduced using a slope failure model that linked bank erosion with bed changes. The study attempted to clarify the meandering development mechanism in the disaster and its predominant factors by using this model. The analysis properly reproduced the characteristics of the post-flood meandering waveforms. Therefore, it is suggested that the development of meandering during the flood attributed to the propagation of meandering downstream, which is triggered by the meandering flow from the meandering channel in the upstream, which also suggests that this propagated meandering then caused a gradual increase of meandering amplitude accompanied by bank erosion in the recession period of the flood.

Highlights

Due to a typhoon and a stationary rain front, a record amount of rain fell in September 2011
Discharge of the largest class was observed in the Otofuke River of the Tokachi River basin, and extensive bank erosion occurred in various parts of the river channel (Fig. 1)
Post-flood surveys revealed the direct cause of the dike breach to be the bank erosion that progressed during the development of meandering flow in the low-water channel

Summary

Introduction

Due to a typhoon and a stationary rain front, a record amount of rain fell in September 2011. In light of the above, this study addresses both the sandbar topography and the planar configuration of the low-water riverbank and conducts various examinations using numerical analysis toward identifying major factors in damage to this river dike. The red line represents the riverbank of the low-water channel along the normal line of river channel, and the blue line represents the main streamline At this point, three large meandering parts had already formed in the upstream section It is reasonable to assume that there was a major difference in the state of the river channel between the upstream side of the KP18.6 area and downstream side of the KP18.6 area In light of this on-site situation, analysis was performed separately for the upstream section versus for www.earth-surf-dynam.net/2/255/2014/. Hereinafter, in order to achieve consistency with previous studies (e.g., Nagata et al, 2013), the analysis was conducted at 1 : 100 scale; in order to www.earth-surf-dynam.net/2/255/2014/

Design flood

Conclusions

A Sandbar development san dba rw ave hei ght Deposition