Characteristics of channel thalweg migration in the lower Yellow River over the past 30 years

The response of channel thalweg is complex temporally and spatially, so investigating the characteristics of thalweg migration is crucial to the river regime and fluvial processes in the lower Yellow River. Section-and reach-scales thalweg migration widths were calculated based on 91 observed cross-sectional profiles during the period from 1986 to 2015, in order to investigate the characteristics of thalweg migration and to identify the key influencing factor of thalweg migration intensity. It is found that thalweg migration processes were reciprocating, and section-scale migration widths in upper reach were larger than those in middle and lower reaches. The magnitude of migration widths decreased dramatically after the operation of Xiaolangdi Reservoir, and it is discovered that the thalweg migration widths in the braided, transitional and meandering reach decreased by 47%, 37%, 41%, respectively. The incoming flow and sediment regime is the dominant factor, although channel boundary conditions (such as floodplain-channel elevation difference, bed material composition) can influence the thalweg migration intensity in the braided reach. The thalweg migration intensity of the braided reach can be expressed as a power function of the previous 4-year average fluvial erosion intensity, and the empirical equation has been verified using the data in 2013-2015.