Abstract: Studies of the high concentration layer (HCL) have great theoretical and practical significance in the protection and utilization of estuarial and coastal areas. In order to better understand the HCL,the physical impacting mechanisms and phase-averaged sediment concentration profile were studied. Combining a 1DV model for the flow-sediment dynamics in the wave-current bottom boundary layer (BBL) and experimental data sets,sensitivity analyses were performed by carrying out computations of several scenarios. Inspired by the 1DV model,the distribution of wave-related sediment diffusivity was proposed,and process-based expressions for the suspended sediment concentration (SSC) profile were derived considering primary impacting factors. Results showed that the HCL is directly related to the wave BBL,which is a combined result of bed forms and flow dynamics. It is not appropriate to establish the relationship of the HCL with a single factor,for instance,the parameters of flow dynamics or bed forms. The effects of stratification and the hindered settling velocity have significant impacts on the HCL. The proposed SSC profile over a flat bed is a distribution of power-Rouse-exponent,while over a vortex rippled bed,it has an exponent-power-Rouse distribution. It is expected that these expressions can be applied in further 2-D and 3-D simulations.