Gravity change and its mechanism after the first water impoundment in Three Gorges Project

In this paper we have analyzed precise gravity survey and gravity effects resulted from water loading,crustal de-formation,ground water level change and precipitation before and after the water impoundment in the Three Gorges Reservoir. We found that: 1 In dam area of the reservoir,gravity effect resulted from water load increase is the most significant,maximum gravity change is 200×10?8 m/s2,but this effect is limited in amplitude and range. Gravity change can be observed about 5 km offshore. The gravity change caused by ground water level change is regional; and the impact of precipitation on it should not be neglected. 2 At head area of the reservoir,the maxi-mum gravity change is near Xiangxi. Monitoring the variation of gravity field and further study should continue in the future.