216 / 2024-02-28 09:49:47

Research on the Characteristics and Influencing Factors of Split Pattern Changes in the Tongling reach of the Yangtze River

lower Yangtze River，The Tongling Reach，Branching channel，fluvial processes，Cause analysis

The Tongling Reach, located at the downstream end of the tide-affected section, upstream from the Datong Reach and downstream from the Heishaozhou Reach, is one of the key reaches of the middle and lower Yangtze River basin. Historically, there have been many sandbars in the Tongling Reach, with major sandbars such as Chengdezhou sandbar and Tingjiazhou sandbar forming various branch river patterns by 1865. After the completion of the Three Gorges Dam, significant changes occurred in the shoal and channel adjustments of the Tongling Reach, altering its diversion pattern and severely impacting navigability. This paper, using topographic and hydrological data from 1998 to 2023, analyzes the changes in the diversion patterns of the Chengdezhou Channel and Tingjiazhouzu Channel before and after the impoundment of the Three Gorges Reservoir, along with their influencing factors, and predicts future development trends. The results indicate that (1) from 1967 to 1998, the left channel of Chengdezhou sandbar was the main channel, but from 1998 to 2023, the diversion ratio of the left channel plummeted to about 42.4% in 2023, indicating a shift in the main distributary; during the same period, the left channel of Tingjiazhou sandbar has consistently been the main channel, maintaining a diversion ratio above 90%, which has gradually decreased in recent years but still retains its status as the main channel. (2) The change in the annual flow process due to the regulation of the Three Gorges Dam is the primary reason for the shift in the main distributary of the Chengdezhou sandbar Channel, as the mainstream swings to the right, leading to erosion at the head of Chengdezhou sandbar and intensified scouring in the right channel. The right channel of Tingjiazhou sandbar experiences an increasing diversion ratio due to the decrease in outlet water levels. (3) With the flattening of the flow process and the downward movement of the main scouring zone, it is expected that the right channel of Chengdezhou sandbar will continue to be scoured, while the diversion ratio of the left channel will continue to decline. The left channel of Tingjiazhou sandbar will maintain its main channel status, and the Nanjiajiang River will continue to develop. However, the increase will be limited due to constraints on inflow conditions.