Experimental study of graded sediments in sinusoidal oscillatory flow

Measurements of concentrations and suspended sediment sizes above well-sorted and mixed sand beds in sinusoidal flows in a large oscillatory flow tunnel are presented. The results show that sediment grading is fundamentally important to the entrainment and suspension of sand from the bed. The depth of bed mobilised by the flow depends on the proportion of coarse sand in the bed, with a greater proportion of coarse sand resulting in a smaller mobilised depth. The distribution of the mobilised sand above the bed strongly depends on the grading. Sand is suspended to higher elevations when the proportion of fine sand is greater. Conversely, a lower proportion of fine sand leads to lower suspended sand concentrations high above the bed and higher concentrations within the sheet flow layer. These observations are intuitively sensible: the experimental results provide quantitative measures of the observations.