Characteristics of Channel Incision Induced by Human Activity in a Wandering Reach in 20 Years

The wandering reach of the lower Yellow River has undergone significant channel degradation since the Xiaolangdi Reservoir operation, with a cumulative channel scour volume of 14.1 x 10(8) m(3) in 1999-2018, and severe channel scour has resulted in rapid channel incision in this reach. The annual and cumulative river bed downcutting depths at section- and reach-scales and water stages at low and high flows were calculated to investigate the characteristics of channel incision quantitatively. The results show that the cumulative river bed downcutting depths at sedimentation sections varied significantly, with the magnitude varying between 1.1 m and 4.2 m. The cumulative reach-scale river bed downcutting depth reached up to 2.9 m and water stages at low flows decreased by more than 3.3 m at hydrometric stations. The previous 6-year average fluvial erosion intensity is the major influencing factor controlling channel incision, and empirical functions were established between cumulative river bed downcutting depths and the previous 6-year average fluvial erosion intensity in the wandering reach and three sub-reaches. The data calculated using the proposed equations agreed well with the observed downcutting depths, so these equations can be used to calculate the processes of channel incision in the recent 20 years in the wandering reach.