基于遥感的黄河下游游荡型河段枯水河势演变规律研究OA

The operation of the Xiaolangdi Reservoir alters the flow and sediment conditions in the Lower Yellow River(LYR).Coupled with the construction of river defense projects,this leads to significant changes in the planform morphology of the wandering reach in the lower rea-ches.Based on long-sequence Landsat satellite remote sensing images and measured runoff and sediment data from 1986 to 2023,this study calculated and analyzed the changing trends in the wandering degree,sinuosity and braiding intensity of the wandering reach after the reser-voir's operation,as well as the spatio-temporal patterns of the upward shift and downward retrogression of the river regime at river training works.Furthermore,the physical mechanisms underlying these evolution laws of the river regime were analyzed.The results indicate that:At the reach scale,the wandering degree shows a significant downward trend under the combined effects of long-term low-flow processes and strong artificial constraints,while sinuosity shows an upward trend and braiding intensity tends to stabilize.The primary causes for the decline in wandering degree are the reduced rate of flood peak rise,the enhanced longitudinal stability of the channel,and the construction of river defense projects.On the other hand,after the operation of the Xiaolangdi Reservoir,approximately 74%of the river training works exhibit a general trend of downward retrogression in space.Temporally,the annual mean distance of the upward shift and downward retrogression at these works correlates with the river scour efficiency and the difference in beach-bed elevation in the reach.Specifically,higher river scour efficiency and smaller beach-bed elevation differences tend to result in an easier occurrence of the upward shift of the river regime.