A study of the transport of graded sediments

Experimental flume data on the initial motion characteristics of size fractions contained in seven graded bed materials are compared with the behaviour of uniform bed materials of similar size. Expected trends in particle stabilities higher thresholds for smaller sizes and lower thresholds for larger sizes in a mixture - are found. One size fraction, DA, in each mixture begins to move under uniform bed material conditions. Whether this size is larger or smaller than D50 inversely depends upon grading. Shielding and exposure effects on particles smaller and larger respectively than DA appear to be common throughout the mixtures analysed.