Activation of scour around bridge abutment

Scour evolution around bridge piers and abutments is a master topic in river hydraulics for the relevance of the process on waterworks stability. Clear water experiments are usually employed to obtain the maximum scour depth, for given obstacle geometry and flow conditions. In this paper new experiments under clear water conditions are presented, performed in the trasitional flow regime, i.e. with grain Reynolds numbers between 5.3 and 9.0. The Reynolds numbers varied between 12000 and 25000. Time evolution of the maximum scour depth changed significantly if the same experiment was repeated, even under neegligible variation of the flow conditions. Therefore, different sets of repetition of the same expertiment were obtained for each flow condition and statistical properties were inferred for each set. Two scour phases were observed during the process, in ageemente with the observation of others. Regression lines and confidence intervals for scour depth evolution were found for each of the two phases. An attempt was made to represent scour evolution in dimensionless units.