Role of bar-channel interactions in a dominant branch shift:The Taipingkou waterway, Yangtze River, China

摘要

Previous investigations regarding river bifurcation mainly focus on the conditions of a stable bifurcation and how key factors affect the asymmetrical features of a bifurcation. In this paper, a numerical case study is presented of the 2012-2014 north to south shift in the Sanba mid-channel bar of the Taipingkou waterway's dominant branch in the Yangtze River, China. Numerical reproduction of the bar-channel system evolution process as well as the resultant shift in the dominant branch was conducted by a fully coupled hydro-sediment-morphodynamic model. The following aspects are shown to play important roles in the shift: the south bank flattening of the Lalinzhou point bar, which formed a straight and wide route for the south branch, and the downstream-south movement of the north-bank Yanglingji point bar, which narrowed the north branch entrance. The direct consequence of these bar evolutions is the north to south shift in the dominant branch. Prior to this shift, the south branch had a larger water diversion ratio during high water but a smaller ratio during low water. Subsequently, the south branch has a larger water diversion ratio when either high or low water levels occur. These findings suggest the important role of bar-channel interactions in dominant branch shifts.