Effects Of Wave Period On The Time-averaged Suspended Sediment Concentration Under The Oscillatory Sheet Flow Condition

Existing experimental data of the time-averaged suspended sediment concentration(TSSC)under the oscillatory sheet flow condition indicates the suspended sediment concentration increases with the increase/decrease of free-stream flow velocity/grain size.However,the existing experimental data cannot uniformly reveal the effects of oscillatory wave period on the sheet flow suspended sediment concentration.Measured TSSC in the sheet flow regime shows that its vertical distribution may increase,decrease,or even remain constant in case that the wave period decreases.Criterion for identifying the relatively fine or coarse sands is introduced based on the non-dimensional ratio between the settling velocity and the root-mean-squared(RMS)flow velocity.If this ratio is less than 0.04?0.043,it is deemed as relatively fine sand.Otherwise,it is classified as relatively coarse sand.With respect to the sheet flow experimental data,it is confirmed that the TSSC for relatively fine sand firstly decreases,then increases and finally decreases once again with the decrease of wave period from 12 to 2 sec;whereas for relatively coarse sand,it almost remains unchanged.Effect of wave period on the TSSC was further demonstrated considering the changes of bed shear stress(i.e.,Shields parameter)with wave period.In order to quantify such wave period effect,the classic gradient diffusion model of suspended sediment was applied.Taking into account the existing experimental data,it is confirmed that sediment diffusivity is insensitive to the wave period.Accordingly,TSSC depends on the reference concentration in case that only wave period changes and other experimental conditions keep the same.Therefore,the ratio of TSSC profiles among different wave periods can be expressed as that of the corresponding reference concentrations,which means vertical distributions of the TSSC under different wave periods are proportional with each other.Accordingly,a quantitative expression of the effects of wave period on the TSSC were deduced and verified with the experimental data.Subsequently,the quantitative analyses of the effects of free-stream flow velocity on the TSSC were also discussed.The corresponding results were verified with the experimental data and the accuracy rate is 90%.