Effect of sediment gradation on erosion by plane turbulent wall jets

This paper presents the results of a laboratory study on the erosion of noncohesive sediment beds made of three different mixtures by deeply submerged plane turbulent wall jets. The sediment mixtures had median sizes of 6.75, 1.32, and 1.62 mm, and geometric standard deviations of 1.32, 2.02, and 3.13. The main objectives were to study the effect of sediment gradation on the asymptotic scour size and determine an effective size for the sediment mixtures for predicting erosion. The experimental observations and analysis presented in this study established that the sediment nonuniformity has a significant effect on the size of the scour hole produced by the jet. The effective size of the sediment mixture for obtaining a good correlation for the depth of scour was found to be d(95) rather than d(50) for defining the densimetric particle Froude number, F-o. The average reduction due to armoring in the maximum scour depth and dune height was found to be similar to 60%, and it was found to be 50% for the scour hale length and the distance of the dune.