| Abstract |
Data from a total of 17 occurrences of scour at seven bridge sites in Louisiana were collected, covering the following ranges: Pier width, 3.4 - 10.4 m; flow depth, 1.7 - 19.5 m; flow velocity, 0.46 - 1.8 m/s; Froude number, 0.067 - 0.189; scour depth, 3.4 - 10.4 m, and bed material median diameter, 0.008 - 0.06 mm. An analysis of the relative scour depth with respect to relative flow depth for flows with Froude numbers about 0.1 shows that the scour depth increases rapidly with an increase in flow depth when the relative flow depth is less than 0.5. The rate of increase then slows down to approach a constant value of 0.8 maximum as the relative flow depth approaches 1.3 and may tend to decrease very slightly as the relative flow depth increases further. For the data where the Froude numbers were about 0.1, Shen's formula II(2) yields the best agreement. Three of the other popular formulas - Laursen's, Shen's formula I and Neill's approximation of Laursen's design curve - tend to overpredict the scour, and three formulas - Ingles-Poona's, Ahmad's and Chitale's - tend to underpredict the scour for these low Froude numbers. |
