## 3 Study Site
### Landslide Activity  
The initial monitoring network of Shengjibao landslide was established in March 2007, which includes 16 horizontal displacement monitoring points (Figure 5). In May 2007, Shengjibao landslide began to deform after the first 156 m impoundment of the TGRA, which was affected by the drop of the reservoir water level and seasonal rainfall. Movement has been small-scale controlled by the topography and generally occurred in the loose soil of the surface layer.  
Figure 4: (**a**) Location of the Three Gorges Reservoir Area (TGRA) in China; (**b**) location of the Shengjibao landslide; (**c**) overall view of the Shengjibao landslide (satellite image from Google Earth).  
The main manifestations are the deformation of some houses, discontinuous cracks on the ground, and ground tilt (Figure 6). The main slide direction of the landslide is 348 degrees and a typical schematic geological cross-section is shown in Figure 7. Based on data collected from March 2007 to December 2015 (Figure 8), four stages of surface displacement along the II-II' profile could be identified (Table 1).  
Figure 5: Monitoring arrangement in the Shengjibao landslide and displacement blocks.  
Figure 6: Deformation indications on the Shengjibao landslide.  
According to the reservoir water level data, the Shengjibao landslide did not show an obvious displacement during the period from March 2007 to May 2007, which was the discharge period after the first 156 m experimental impoundment of the TGRA. The operation period of the low water level (145 m) in the flood season of the reservoir was from 1 June 2007 to 20 September 2007. Reservoir water level fluctuations were not significant during this period. However, landslide deformation, characterized by increased displacement of the monitoring points, was obvious during this period, with rainfall being the dominant control on landslide deformation. From October 2007 to January, 2008, the reservoir water level rose again to 156 m. But the displacement of landslide monitoring points did not change significantly during this period.  
The displacement data showed a sharp increase in surface displacement in August and September 2013 (Figure 8). However, a similar pattern was not detected in August and September 2014, despite comparable rainfall levels. According to the precipitation data showed in Figure 9, there was a rainfall  
\begin{table}
\begin{tabular}{c c c} \hline
**Deformation Stage** & **Time Range** & **Remarks** \\ \hline
1 & March 2007–May 2007 & Landslide deformation starting stage. \\
2 & June 2007–October 2009 & Increased deformation, the first fluctuation of 172 m. \\
3 & November 2009–August 2011 & Steady deformation stage, the first fluctuation of 175 m. \\
4 & September 2011–December 2015 & Deformation has periodic and trend characteristics except August and September 2013. \\ \hline \end{tabular}
\end{table}
Table 1: Deformation stages of the Shengjibao landslide.  
Figure 8: Rainfall, reservoir water level, and cumulative displacement monitoring data from the landslide area.  
Figure 7: A Schematic geological cross-section II-II’ of the Shengjibao landslide.  
pattern that lasted for 15 days during the period in 2013, and a rainfall pattern only lasted for 9 days in 2014. This indicates that under the same fluctuation conditions of reservoir water level, a longer duration of rainfall has a more important influence on landslide deformation.