Analysis of water-sediment characteristics and influence factors of upper and lower river reaches before and after impoundment of Three Gorges Reservoir
The deposition of sediment is one of the key technical problems of the Three Gorges Project, which is related to utilization of water resources in Yangtze River, ecosystem and environmental protection and economic development. This article obtained hydrological and sediment monitoring data of 11 important control hydrological stations from 2002 to 2016 at the upper and lower reach of the Three Gorges Reservoir, systematically studied the variation characteristics of hydrology and sediment parameters, correlation between hydrologic and sediment parameters, erosion and deposition characteristics of the Three Gorges Reservoir, and explored the reasons for the change of sediment characteristics. The results showed that the water storage of the Three Gorges Reservoir includes impounding during construction, early and trial impounding, which has a great influence on the water-sediment characteristics of upper and lower reaches of the Three Gorges Reservoir. The greater the influence is the closer to the dam. The water level was raised by the Three Gorges Reservoir, which caused the velocity of most upstream rivers became smaller, river flow section and hydrodynamic condition changed, the amount of sediment was less and less, and sediment grain size was finer. Cascade hydropower stations were built on the Yangtze River and tributaries on the upper reaches of the Three Gorges Reservoir, a lot of silt has been retained, annual sediment load, annual average sediment concentration, mediansize of sediment, modulus of sediment transport decreased dramatically. Annual runoff and sediment discharge, annual average sediment concentration, modulus of sediment transport had a good correlation during 2004 - 2013, change rule of curves are similar, there was a weak correlation after the impoundment of the Three Gorges Reservoir in 2013. Annual runoff can characterize the change characteristics of sediment parameters. Annual sediment load and annual average sediment concentration had a good correlation during 2004 - 2013. Sediment volume of the Three Gorges Reservoir showed an increasing trend before 2007, and then sediment volumen of the Three Gorges Reservoir gradually decreased. The water level of the Three Gorges Reservoir in flood season had a great influence on the scouring and silting, sediment characteristics of reservoir, high water level in the dry season had little effect on them. The results will provide theoretical support for planning and design of cascade hydropower stations and channel in the Yangtze River Basin, operation and management of the Three Gorges Reservoir.