Quantification of extent of scour using the Erodibility Index Method

The paper presents an overview of applying the Erodibility Index Method to predict extent of scour. With the variation of the erosive power of water as a function of space and time known for the flow conditions under consideration it is possible to predict scour extent for any flow condition and any earth material by using this method. Methods to determine spatial and temporal variation in the erosive power of water can be determined by developing equations from basic principles of hydraulics, empirical methods, physical hydraulic model studies or computer simulation. This paper presents two examples that use empirical relationships determined by physical hydraulic model studies. The one example relates to scour around bridge piers and the other to plunge pool scour. A summary of the Erodibility Index Method that is used in this approach is provided in a companion paper to this volume ( Annandale 2002a ) as is the method that is used to quantify the relative ability of rock to resist scour (Annandale 2002c).