## 4 Discussion  
Evaluating the effect of landslide engineering remedial works at the regional scale is a relatively unattempted task and, even at the slope scale, is usually time-consuming and highly empirical: For instance, researchers attempted to build an evaluating system considering factors from different aspects employing an integrated fuzzy hierarchy process theory [24]. The main purpose of this study is to propose a multi-scale integrated monitoring method to prevent landslide remedial works from invalidation. It is true that a remedial work's effectiveness may be considered inappropriate or seriously damaged only with very large deformations; however, a monitoring program, like the one proposed, may identify precursor signs that could allow for intervention before reaching critical conditions. The presented methodology is low-cost, easy to perform, and very straightforward to communicate to citizens and authorities. According to the requirements of the local government administration, casualties, and property losses caused directly by geohazards in the TGRA should be completely eradicated, and, consequently, large investments on scientific research and on hazard mitigation have been undertaken. Our study proves that, up to now, great accomplishments have been achieved: Overall, the engineering remedial works in the Wanzhou to Yunyang reservoir section played a significant role in the landslide control as most of the controlled landslides remained inactive, and most of the active landslides were not controlled with engineering remedial work. The majority of the controlled landslides are no longer being carefully monitored, as typically the designs of controlling projects are relatively safe and hiring other forms of monitoring equipment is considered as an avoidable investment. Thus, it is hard to obtain other sources of monitoring data to observe the difference of deformation rates before and after the remedial works [35,36]. In such condition, the joint use of InSAR data and field investigation became the most direct and reliable mean to detect possible criticalities and to study the evolution process of controlled landslides [19,20]. The results of our application also showed that remote sensing technologies alone were not sufficient to  
Figure 12: (a) PSInSAR deformation rate map of the Kangjiapo landslide. (b) Pier sinking observed at the middle part of the landslide body. (c) Anchors at the trailing edge of the Kangjiapo landslide. (d) Anchors at the landslide middle part of the landslide. obtain complete and reliable information. For example, as we reported in the results section, owing to the relatively short interaction time between the engineering remedial work and the sliding body, it is difficult to determine whether the landslide remedial work is valid or not in the Dadiping landslide. Thus, further attention should be paid over the next few years, and periodic field investigation or even ground monitoring instrument are highly recommended; besides, although a series of active PS spots were observed at the Kangjiapo landslide, the reported deformation of the bridge pier was still hard to capture. InSAR can detect deformation related to the interaction between the ground and infrastructures; however, it is not suitable to measure internal deformation of the structure itself. Although the general trend of the deformation is captured by the InSAR time-series analysis, the detailed and short-term displacements are not always completely in accordance with the GPS data. This is likely due to the inconsistency between the projection direction of the InSAR displacement results and the GPS data, and the lowest spatial and temporal resolution of the accessible SAR images; however, this drawback did not prevent us from recognizing a potential instability hotspot in the framework of a regional scale investigation.