Assessing the physical vulnerability of check dams through an empirical damage index

A comprehensive analysis of flood risk in mountain streams has to include an assessment of the vulnerability of the protection systems, in addition to an assessment of the vulnerability of the constructed environment on alluvial fans and floodplains. Structures forming the protection systems are of a dual nature, i.e. they are designed to mitigate natural process-related hazards and, on the other hand, are prone to be damaged during their lifecycle by the same processes they should mitigate. Therefore, their effectiveness declines over time. Hence, the knowledge of how effectively control structures perform is essential for risk management. A procedure was developed to assess the physical vulnerability of check dams based on empirical evidence collected in South Tyrol, Northern Italy. A damage index defined on pre- and postevent comparisons of check dam conditions was evaluated for 362 structures in 18 mountain streams along with the relevant processes and the structural characteristics affecting it. Although the available dataset did not allow conclusive functional relationships between damage index and impact variables to be established, it was possible to assess the average expected residual functionality of check dams according to structure characteristics, and event type and intensity. These results may help plan appropriate check dam maintenance.