A laboratory study of suspended sediment dynamics under waves for non-uniform sands

Time series of suspended sediment concentration and particle size distribution for regular waves over rippled beds were measured in the laboratory using the Sequoia Scientific LISST-1000 (L&barbelow;aser I&barbelow;n-S&barbelow;itu S&barbelow;cattering and T&barbelow;ransmissiometry). Two sand beds, one nearly uniform and the other more graded, were used to explore the effects of sediment gradation on suspended sediment dynamics. All runs were compared with previous studies, including theoretical and empirical relationships and other laboratory and field measurements. It was concluded that the LISST-1000 could produce reliable measurements of both suspended sediment concentration and size distribution (for sands) when compared to other multi-parameter instrumentation. Small changes in sediment gradation were found to alter the suspended sediment concentration considerable. Predictions of the time-averaged suspended concentration over rippled beds (Nielsen, 1986), which use the d₅₀ of the sand bed as the characteristic diameter, significantly overestimated the suspended sediment transport for both sand beds. The sediment diffusivity, ϵ _s, was found to remain constant with height, as predicted by Nielsen, 1986. The mean diameter of the sediment in suspension was found to be lower than that of the sediment beds and to vary widely with wave phase.