Analysis on the Criterion for Channel avulsions of the Costal Delta in the Yellow River

Abstract:

Based on the data analysis and simulation on the channel avulsions in the past 60 years in the Yellow River, a critical shear stress τ_c=ρgR_cS_c was found to be a criterion of channel avulsions of costal delta in the Yellow River. That means there are two controlling factors impacting the processes of channel avulsions: (1) R_c—bankfull hydraulic radius of transverse section of the bifurcation point, which is determined by inputting water and sediment conditions upstream; (2)S_c—local riverbed slope of the bifurcation point, which exhibits a good nonlinear relation with the channel length downstream from the point to the sea. The results in this paper imply that: firstly, the channels in the estuary are divided into two states: stable when τ>τ_c, non-stable (channel avulsion) when τ<τ_c; Secondly, channel avulsions of costal deltas of alluvial rivers are determined not only by inputting water and sediment conditions upstream (impacting on transverse sections), but also by base eroding levels in estuaries downstream (impacting on longitudinal sections).