Lateral Migration in a Wandering Reach of the Middle Yellow River in Response to Different Boundary Conditions

Abstract

The Xiaobeiganliu reach is a typical wandering reach of the Middle Yellow River that has rapid and significant channel lateral migration, which may threaten the safety of riparian land and flood control structures. To investigate the characteristics and mechanism of lateral migration in the Xiaobeiganliu reach, the temporal and spatial variations in bankfull width and thalweg migration distance were identified during the continuous deposition period, quantitatively analyzing the effect of different boundary conditions on the lateral migration index. The reach-scale bankfull width decreased by 32% from 1986 to 2001 because hyperconcentrated floods often occurred in this reach. The thalweg migration distance varied dramatically at cross-sections, with the maximum annual thalweg migration distance reaching 4290 m. The lateral migration index of the Xiaobeiganliu reach responded well to the upstream and downstream boundary conditions. The previous 3-year average water discharge and 4-year average sediment concentration at the upstream station were two key fluvial factors influencing lateral migration, with the relation being established between the lateral migration index and the two parameters. The Tongguan (TG) elevation was the key downstream boundary condition affecting thalweg migration, and a power function was proposed between the lateral migration index and the variations in annual TG elevation.