## 3 Methodology for Evaluating the Effectiveness of Rock Fall Protections
### Re-Evaluation of Hazard at the Study Site
#### 3.3.3 Account for the Effect of Protection Measures in Hazard Zoning  
If the application of Equations (14), (19) or (20) shows that the reduced capacity is lower than required to handle the hazard, the protection measure concerned must be considered as totally unserviceable. Its presence on site should therefore not be accounted for in hazard analysis and the measure should be repaired (if possible) or replaced with a new one, in order to lower the hazard at the level required.  
On the other hand, if the reduced performance capacity is still sufficient to decrease the hazard, the mitigation effects of the protection can be included in the hazard assessment, provided some cost-effective maintenance works (to be established case by case) would still be taken, to restore at best its capacity towards optimal. In this case, starting from the location of the protection \(x_{P}\) and proceeding down along the slope to the limit of the runout area, the corresponding hazard zoning maps can display the same effects as if the protection were in optimal performance conditions.  
In particular, to clearly distinguish the situation in which a lower degree of hazard derives from the rock fall scenario itself, without any account for any measure, from the situation in which that hazard degree is obtained thanks to the performance of protection measures, all areas reclassified based on the effects of rock fall protections will be represented on the zoning maps as hatched zones. The hatched pattern will show the specific colour codes and/or textures corresponding to the hazard levels computed both with and without account for the protection. Such a representation underlines that the hazard level at the areas concerned must be intended indeed, as the one expressed by the colour corresponding to the lower level in the hatched texture but, at the same time, that it was possible to achieve this level only by means of protection measures.  
As an example, Figure 2 shows these concepts applied with the help of a rock fall intensity-frequency diagram. In particular, the diagram used in Switzerland for rock fall hazard zoning is considered [6; 7], in which the combination of rock fall energy and return period originates three levels of hazard (low, moderate and high), each corresponding to a given colour code--plus a fourth level designated as \"residual hazard\", for all events characterised by T > 300 years, independently from their energy (not considered for the sake of simplicity). Starting from any of the three main levels of hazard, the figure shows all possible reductions to a lower (down to null) level and the related use of hatched-colour codes, as a function of what mitigation can possibly achieve compatibly with cost-effectiveness, risk perception and acceptance criteria. In the figure, the hollow circles on the diagrams represent the initial hazard, with no account for any protection measure possibly present, while the filled circles the final hazard, after the mitigation effect of the protections is considered (where the mitigation can be due either to an optimal or, at least, to a reduced performance capacity of the measures, but still such that the measures can operate properly).