A reappraisal of bridge piers scour vulnerability: a case study in the Upper Tiber River basin (central Italy)

The issue of bridge piers vulnerability to scour is addressed by comparing two procedures. The first method quantifies the Scour Vulnerability Index (SVI) considering the combined effects of local and contraction scour. The method requires that a scale factor, for taking account of the scour depth overestimation provided by empirical formulae, is quantified for the selected case study through inspection campaigns. The second approach identifies a vulnerability index to vertical instability depending on several indicators. The study is carried out for a sample of 46 bridges in the Tiber River basin, central Italy, and shows that the two methods identify the same number of piers affected by 'high' vulnerability. Results are supplemented by outcomes of inspections that identified, through the scale factor, a high correlation between measured scour depth and SVI value. SVI, simpler and most practical, seems useful for an expeditious estimate of scour vulnerability in large areas and can be adopted by decision makers to identify the structures requiring attention in terms of maintenance and control. The presented results do not provide a general rule for a correct estimate of scour. They refer to solely the investigated case study and need to be verified in other rivers context.