Why does the Yangtze River slow down when it reaches the plains of Hunan and Hubei?

When the Yangtze River exits the Three Gorges Dam near Yichang, it enters a complex, low-lying region of Hunan and Hubei provinces characterized by extensive alluvial plains at elevations below 165 feet (50 meters).

The river slows down in this area primarily because it transitions from a confined, mountainous course into a vast, flat landscape featuring a complex network of multiple river channels, marshes, and large lakes, such as Dongting Lake. This region acts as a natural flood-regulation basin where the river's flow is influenced by the influx of several major tributaries, including the Yuan, Xiang, and Han rivers, as well as significant fluctuations in water volume caused by the surrounding lake systems.12