Temporal and spatial evolution characteristics of the current tail channel of the Yellow River: Processes and mechanisms

The Qingshuigou Channel, as the current tail channel of the Yellow River, formed by the diversion of the Diaokou River in 1976, has undergone a particularly dramatic spatio-temporal evolution, and its evolution processes and the underlying mechanisms are still unclear. On the basis of the flood season cross section data for the river downstream of the Lijin Hydrological Station from 1976 to 2017, the current study calculated the main channel morphological characteristics of the tail channel in different reaches using a reach-scale morphological parameter calculation method and K-means clustering analysis. An elevated riverbed index was proposed to identify the elevated riverbed situation of the river channel. The results show that from 1976 to 2017, the bankfull area experienced repeated processes of decrease and increase, and the main channel morphology gradually changed from wide and shallow to narrow and deep over time. For most of the time period, the conveyance capacity of the main channel gradually decreased from upstream to downstream. The elevated riverbed situation gradually became more severe along the river reach from 0 to 85 km away from Lijin, but was less severe in the reach more than 85 km downstream of Lijin. The most severe elevated riverbed situation appeared mainly in the range of 71–83 km below Lijin in 1991–1995. When the sediment-carrying capacity of the water flow was strong, the bankfull area of the main channel increased, and the elevated riverbed situation was alleviated. River channel projects have helped to maintain the narrow and deep shape of the main channel, but the installation of farm dikes have aggravated the elevated riverbed situation. At the same time, extension and diversion of the tail channel have changed the erosion base level, greatly affecting the evolution of the channel morphology. The current study has provided a typical case for exploring the processes and mechanisms of tail channel evolution.