Human impact on river channel changes downstream of Changzhou hydro-junction on the Xi River (Xijiang), China

摘要

Dams impose changes of flow and sediment transfer. In addition due to release of clear water and unsteady flow during dam operations, the downstream channel bed tends to erode. The degradation process may be greatly aggravated by human impacts, including river sand mining and channel restoration projects, which probably produce a large drop in water level. When the changes are beyond estimates, the safety of waterway navigation is threatened because the water depth at the ship-lock is not sufficient to accommodate a ship's draft. It is especially problematic when this occurs in the near-dam reach downstream of the hydro-junction. Changzhou hydro-junction, a low head hydro-electric station located downstream of the Xijiang River in Guangxi province of China, provides power generation, navigation, and flood control. It is famous in China as the world's largest river ship-lock, having four-parallel lock chambers. However, the first double lock chambers, completed in 2007 have been facing a navigation crisis caused by low water levels, and the other double lock chambers went into construction two years later. On the basis of the field topographical and hydrological data, this study analyzed variations of the river bed and low water levels. Furthermore, it studied the channel responses to multi-factors dominated by human impact. The results show that during the early years of Changzhou dam impoundment form 2007 to 2012, the diminishing water level under the same rates of discharge has largely resulted from integrated dam operations factors, extensive mining, and channel restoration. Furthermore, the latter two were the main factors that caused the present low water level. These results provide a valuable reference for channel regulation.