The typology, frequency and magnitude of some behaviour events in case of torrential hydrographical management works in the upper Tarlung watershed

During the 20-25 years from their startup, the torrential hydrographical management works carried out in the upper T rlung Watershed (55 dams, 22 sills, 25 traverses and 4 outlet canals) have exposed a number of 24 behaviour event types: 13 out of them reduce the safety of exploitation and the sustainability of the works (hereinafter called damages), while the other 11 reduce the functionality of the works (hereinafter called disfunctionalities). The following behaviour events have the highest frequency:(i) damages caused by water and alluvia erosion (erosive damages), followed by breakages, in the category of damages, and (ii) unsupervised installation of forest vegetation on the managed torrential hydrographical network and apron siltation, in the category of disfunctionalities. For methodological reasons, only the erosive damage of works was successively analysed, according to two criteria: the average depth (cm) in the eroded area and the percentage of the erosive area out of the total surface. Further on, by combining the two criteria for analysis, five representation areas with the same damage intensity were defined (very low, low, medium, high and very high intensity). With the aid of the event frequency values recorded in these areas and of the coefficients attributed to each intensity class (from 1 for very low intensity to 5 for very high intensity), the author reached the conclusion that the level of the recorded intensity of the damage caused by water and alluvia erosion ranged from very low to low.