Effects of large upstream reservoir operations on cross-sectional changes in the channel of the lower Yellow River reach

Abstract

The lower Yellow River (YR) reach is one of the most typical and complex river channels in the world. The impact of human activities on the evolution of its channels is an important scientific issue that needs to be explored. Based on cross-sectional channel data measured at four typical hydrological stations in the lower YR during the period from 1965 to 2015 and the accompanying annual runoff and sediment data, the variation characteristics of the longitudinal slopes of the riverbeds, the width-depth ratio of the cross-sections, and the lateral migration of thalweg points were analyzed. The river phase coefficients (ξ = W1/2/H) of the YR channel across different years were further evaluated. Furthermore, the correlation relationship between the river phase coefficient, annual discharge, and sediment concentration was established. The results show that over the last five decades, the fluctuation of the longitudinal profile of the upper and lower parts of the lower YR was more obvious than that of the middle part, and the variation range of the width of the channel cross sections and the fluctuation of the mainstream line differed in 1965–1973, 1974–1980, 1981–1985, 1986–1999, and 2000–2015. The morphological parameters of the channel cross-section (ξ) were mainly affected by the annual average discharge and sediment concentration, and a good fitting relationship was found through quantitative analyses. Large reservoirs have the function of redistributing water and sediment yields and reducing peak discharges, thereby leading to changes in the erosion-deposition patterns and river morphologies of channels.