Method for Obtaining Prototype Local Scour Depths from Physical Model Tests

Physical models are used in many areas of engineering to obtain information about prototype situations. Ideally, the important dimensionless groups for the problem being examined are made the same for the model and prototype. When this is possible there is no question about the relationship between the quantities being measured in the model and their corresponding values in the prototype. There are, however, situations where all of the important parameters cannot be maintained constant and this creates a problem when estimating values for the prototype from measured values in the model. In modeling local scour at bridge piers such a problem is encountered when the prototype sediment is sufficiently small that it cannot be scaled using the geometric scale for the model. This paper presents a method for scaling measured local scour depths in physical model tests to prototype conditions based on scour prediction equations developed by the lead author. The method is demonstrated using data from laboratory tests conducted with circular piles ranging in diameter from 0.114 m to 0.914 m.