ABSTRACT
Research in recent years has begun to acknowledge the importance of debris accumulations at bridge piers, with particular emphasis on the effects that debris jams have on bridge stability and flood risk. The constriction exerted by the accumulated debris induces an accelerated flow that exacerbates the scour at the base of the pier, as well as causing the increase of the up-stream level. However, a key-point for engineers and practitioners is to identify those structures that are liable to debris accumulations, in order to plan and design mitigation works and counter-measures. To this end, it is proposed a quick and cost-effective methodology for assessing bridges that are prone to debris accumulations by using satellite imagery widely avail-able to the public. Currently, satellite photos allow tracking over time in given locations and for several years. In this work it is shown that in main rivers this type of analysis uncovered a large portion of bridges (in the range between 25% and 60% of the total bridge stock) in the two main Italian rivers (i.e. Po and Tiber) where debris repeatedly accumulated over the years covered by the satellite pictures. Furthermore, other examples in USA showed that accumulated debris formed and removed in short period of times, as well as recurring to the same piers or abutments. However, this methodology may not be applied to those rivers with size and features that would impede a correct vision of accumulated debris, in which case other approaches would be required.
