# Past, Present and Future Monitoring at the Vallcebre Landslide (Eastern Pyrenees, Spain)
## 4 Summary and Conclusions  
A general overview of the methods used in Vallcebre for measuring the displacements of the landslide has been given. More details of the systems presented here, along with the full formulation, validation and conclusions, can be found in [1; 4; 5; 6; 7]. To conclude, we present here some lessons learned during the progressive monitoring of the Vallcebre landslide since 1987. A summary of the main characteristics of the methods is given in Table 1. This table is in accordance with [5; 9], but the values are valid only for the specific constraints and equipment in Vallcebre. The characteristics of the methods are summarized along with the precision and main results achieved. The 'Precision' figures seek to characterize the'real' or field performance of the systems in our landslide instead of the theoretical values that can be found in the instrument's technical specifications. The latter were determined in lab conditions and were found to be too optimistic, in general. The 'Complexity' column aims to quantify the refinement of the equipment and personnel involved, and the 'Cost' column includes the amount of instrumentation, installation and work needed to obtain the data. The methods in the table should not be considered as excluding alternatives, but rather, as complementary systems to be applied progressively or in different areas, as has  
been explained in Section 2. For instance, the photogrammetry was used in the toe of the slide to monitor a fairly small but very active area. EDM and triangulation (and later the GPS) were implemented to cover the whole hillside and capture mean movements as big as 1 m per year with minimum investment. The surveying with EDM and GPS were carried out with a given frequency (i.e., campaigns each two months or each year), so the results are discontinuous over time. As stated in note 'c' in Table 1, although not implemented in Valleebre, it is technically possible to automate the procedure for the continuous monitoring of the displacements. On the other hand, the GPS results helped to calibrate the parameters of the wire extensometer equation [4]. The installation of these in-hole devices was possible only when additional funding was obtained in order to drill the boreholes and instrument them. The inclinometers and the in-hole wire extensometers complement each other very well. As the landslide was fairly active, the inclinometers had a short 'life', but produced high-quality information on landslide displacement profiles, velocities and the position of the shear surface quite immediately after their installation. In contrast, at the early stages of deformation, the wire extensometers may only record negative displacements, which are not easily related to the superficial ones. However, once the inclinometers were lost, the wire extensometers provided continuous recording, even for very large displacements. Since 1996, when they were first installed, the wire extensometers have provided a measurement readout each 20 min; at some points, the cumulative displacement has been as high as 6 m. The accelerations in the rate of displacement can be easily related to rainfall and groundwater rises (Figure 14), especially during critical rainy events, when other systems are not in operation. Most of the piezometers and 3 wire extensometers installed in Valleebre were still operational in 2012. Around 2010 an automatic meteorological station was installed in the center of the landslide in order to get the significant precipitation, because the rainfall may vary sharply from one point to another. Redundancy between methods is advisable in case of malfunctions in the devices or as a means to cover gaps in data. As shown in the previous sections, all the results are in fairly good accordance when adequate corrections are applied (Figures 22 and 23). Prior to the comparison of the different techniques, some error considerations must be made, in particular, the filtering of any systematic errors (Figures 24 and 25, for instance).