Applicability Analysis of Pier-Scour Equations in the Field: Error Analysis by Rationalizing Measurement Data

Previous literature has shown unsatisfactory validation of the existing equations predicting pier-scour depth with laboratory and field data. In an attempt to find the reasons for the unsatisfactory comparisons, we examined the performance of the Chinese equations with several other equations through in-depth analyses of the errors and explored the possible error-causing factors both in field measurement data and the proper use of parameters. Results show that the Chinese equations underpredicted scour depth for all the laboratory data and for field data under clear-water conditions. The Chinese equations performed better for field data under live-bed conditions compared to the other (i.e., laboratory, or clear-water field) conditions. The other equations overpredicted scour depth for both laboratory and field data. Uncertainty of the field data associated with measurement accuracy results in large errors, especially when scour depth is less than 1 m. The flood duration in the field is usually far shorter than what is needed to reach the equilibrium scour depth that the equations are attempting to predict for safe design, which contributes to the larger predicted scour depth than measurements. The effect of some parameters (e.g., sediment size, pier width, and incipient velocity for local pier scour) should be modified in the Chinese equations under fine-sediment and/or wide-pier conditions.