The impact of dams on the river connectivity of the two largest river basins in China

Dams are built on rivers for power generation, flood prevention and control, and water resources utilization. However, dams also reduce the connectivity of rivers, which hinders the exchange of material and organisms within rivers. The Yangtze River Basin and the Yellow River Basin are the two largest river basins in China. In this study, the connectivity of these two huge and highly impacted systems was investigated. The Dendritic Connectivity Index (DCI) was applied to evaluate the impact on river connectivity of dams with a reservoir capacity of larger than 0.1 km(3). The results show that river connectivity decreased following an increase in dam construction. The connectivity of the Yangtze River Basin was close to 80 (0 is completely disconnected and 100 is connectivity under natural condition) in the 1980s, but declined significantly after the Gezhouba Dam was constructed on the mainstream of the Yangtze River. From 1980 to 2010, the connectivity of the Yellow River Basin was always lower than that of the Yangtze River Basin. The changes in the connectivity indices of potamodromous fish (DCIp) and diadromous fish (DCId) were determined for the period of 1980-2010. In the Yangtze River Basin, the DCIp decreased by 67.28% and the DCId decreased by 65.72%. In the Yellow River Basin, the DCIp decreased by 43.8% and the DCId decreased by 100%. In conclusion, the construction of dams, especially those on the main stream, has reduced the connectivity of the basin. The connectivity of the Yangtze River Basin and the Yellow River Basin has been severely affected.