Effects of Delta Extension on Base Level Rising of the Lower Yellow River

Shan Zheng, Guangming Tan, Baosheng Wu, Colin Thorne

Friday 3 july 2015

8:30 - 8:45h at Antarctica (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) Morphodynamics of estuaries and coastal areas

Parallel session: 14A. Sediment - Coast

Owing to channel avulsion and extension of the Yellow River delta in response to sediment deposition caused by heavy sediment load entering the estuary, the water stage at a discharge of 3000 m3/s (denoted by H3000) at Lijin station (the endpoint of the LYR) rose by 2.5 m during 1950 and 2000 with an average rate of 5 cm/a. As the local base level of the lower Yellow River, rising of water stage or channel bed elevation at Lijin station is significant for long-term evolution of the channel reach. Impacts of water and sediment conditions and delta evolution on changes of H3000 at Lijin were analyzed in this study. Results showed that every time after channel avulsion at the Yellow River delta, the river length was suddenly shortened and channel slope increased abruptly. Then channel length increased at a decreasing rate, while channel slope decreased at a rate decaying exponentially with time and reached an equilibrium value after 5~6 years. This phenomenon indicates a significant characteristic of the delayed response of the fluvial system. Considering the difference in channel evolution upstream and downstream of the diversion point of the delta channel, four different generalized models for the longitudinal changes of the delta channel were proposed. Equations for calculating H3000 at Lijin and Xihekou (a recent diversion point of the delta channel) stations were developed by using the delayed response model for modeling morphological responses of fluvial rivers to perturbation. Calculated results for H3000 at Lijin and Xihekou stations showed that the proposed methods, by considering the impacts of incoming water and sediment conditions and channel length of the Yellow River delta, can simulate the long-term changes of the local base level of the LYR. The proposed methods can be used not only for prediction of base level changes of the LYR with data available, but is also helpful for further understanding of the mechanism of the local base level changes in response to both the variation of water and sediment conditions and the delta evolution.