Decadal Hydro-Morphodynamic Evolution of a Sandy Meander Bend Downstream of the Three Gorges Dam and Impact on Waterway Navigation

Abstract

The Three Gorges Dam (TGD) in the Yangtze River profoundly regulates the downstream river discharge and sediment load, causing significant river morphodynamic changes since 2003. Understanding such changes is vital for managing the navigational waterway. Using the Wakouzi waterway 190 km downstream from TGD as an example, we examined its decadal hydro-morphodynamic evolution based on hydrological and topographical data collected from the 1990s onwards. The results showed that the suspended sediment load has reduced by 85.8% downstream of TGD, although the annual runoff has not changed. The suspended sediment has become coarser due to depletion of the fine sediment source. As a result, the river channel has been substantially eroded, particularly the deep-water parts of the channel. Erosion of the elongated sand bars has emerged as well, even in the presence of channel regulation works. Consequently, channel degradation has led to a lower river stage under the same river discharge compared with the pre-TGD condition, particularly in the dry season with a lower river discharge. These changes imply worsened navigability of the examined riverbend. The results of this study have implications for management of other river reaches in the middle Yangtze River and other rivers undergoing similar changes worldwide.