Comparison of pier-scour equations using field data

Over the past 25 years, numerous studies have been conducted and equations developed to predict bridge-pier scour. Most of these equations were developed using laboratory data and sometimes tested using limited field data. Until recently, there have been very limited data to test the equations, and so there is considerable uncertainty in the use of these equations to predict scour in field settings. For a number of the equations, the conditions under which the laboratory experiments were conducted are unknown. In addition, the ranges of the various parameters over which the equations are valid are also typically unknown. Even if the range of data used in the laboratory study is known, it is quite uncertain as to how those ranges, using small-scale models, correlate to prototype conditions. The purpose of this study is to compare seven bridge-pier-scour equations using a large set of field. Data for both live-bed and clear-water scour will be examined; although during most floods the stream bed is live, there are cases, such as at relief bridges and in coastal areas, in which the water remains clear. The limitations of each of the equations will be examined for the purpose of providing guidance to hydraulic engineers concerned with scour at bridge piers.