Abstract
Although channel bipolarization has various effects on river channel management and is regarded as a problem, there are very few studies on the relationship between the relative bar height and riverbank erosion based on the data observed in natural rivers. In this paper, we set a bipolarization index (i.e., gravel bar height-bankfull depth ratio; hereinafter, referred to as B-index) and examined the relationship between the bar shape before flooding and riverbank erosion frequency after flooding in four rivers in Hokkaido. Our results show that the width of bank erosion and the frequency of bank erosion tended to increase as the B-index increased. In the channel with alternate bars, the frequency of bank erosion tended to increase sharply at the B-index of 1.0 or higher. Although the sample size of channel with double-row bars is small, the considered sample size shows that the bank is likely to be eroded during floods since the averaged bank height is low relative to the averaged bar height. The results of this study clearly show that the B-index can capture the risk of bank erosion in gravel-bed rivers.
