Use of Monitoring Data to Interpret Active Landslide Movements and Hydrological Triggers in Three Gorges Reservoir

The primary objective of this research is to study the relationship between surface movement and hydrological triggers of a large and active landslide in the Three Gorges Reservoir (the Shuping landslide). When the landslide was reactivated in June 2003 owing to the impoundment of the Three Gorges Dam, measurement of surface movement began through the use of manual global positioning system (GPS) monitoring. Since June 2012, near-real-time data with fine temporal resolution have been collected through the use of continuous automatic GPS. In total, more than 10 years of surface movement have been recorded for the Shuping landslide. Patterns of surface movement have been spatially identified first, and then subsequently over time. A fast moving zone can be spatially identified from the primary deformation zone. The temporal evolution of the landslide consists of a typical stepwise progression in time with short periods of fast movement (FM) and longer periods of slower movement. Eight of the former have been identified. The hydrological conditions and triggering factors can be understood by performing detailed correlations between displacements and daily fluctuations of reservoir water levels and rainfall records. The results indicate that any continuous rapid drawdown of the reservoir water level from approximately 160 to 145 m will definitely trigger FM. Generally, there is a lag time of approximately 6 days after the water level is reduced. In addition, there is a definite correlation between fast velocity and the rate of drawdown. Meanwhile, prolonged and periodic intense rainfalls have a slightly relevant effect on the movement of this landslide. This shows that long-term and near-real-time monitoring are invaluable for the understanding of landslide movements and their hydrological triggers.