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Abstract: Appropriate descriptions of turbulence are important in predicting sediment transport and seabed evolution. We use here a three-dimensional model to investigate the impacts of sediment-induced stratification, erosion parameterization, and turbulence closures on sediment transport and morphological simulations. The model is implemented in the Proudman Oceanographic Laboratory Coastal Ocean Modelling System (POLCOMS), which couples a hydrodynamic model to the General Ocean Turbulence Model (GOTM) and to a sediment transport model. This sediment transport model calculates both suspended sediment concentrations and bed evolution. A large number of turbulence closures can be tested and we focus on the methods used to calculate the turbulent length scale and the stability functions. Different modelling scenarios are assessed against experimental data of velocity profiles, suspended sediment concentrations, and trench migration in a laboratory flume. Numerical results show that the processes investigated have little impact on the flow velocity profiles, in spite of some differences on the bed shear stress. The only exception is the one-equation turbulence closure, which cannot reproduce velocity profiles appropriately. Sediment-induced stratification, erosion parameterization, and turbulence closures can all have significant impacts on the suspended sediment concentration and the bed evolution. Model-data comparisons are found to be particularly sensitive to the method used to calculate the turbulent length scale. [Copyright &y& Elsevier]

The role of bore turbulence for sediment transport in the swash and inner surf zones is investigated using field measurements of (a) cross-shore velocity using an electromagnetic current meter at z=3 cm, (b) turbulent kinetic energy (TKE) and cross-shore velocity using a 3-dimensional acoustic Döppler velocimeter at z=7.5 cm, (c) water depth using a pressure transducer at z=0, and (d) suspended sediment concentration (SSC) using seven miniature optical backscatter sensors at z=1–32 cm, on a steep beach in high energy conditions (Hb≈1.6 m). High SSC and high TKE values were associated with the passing of the bore front while the near-bed flow was undergoing rapid onshore acceleration. Peak TKE values tended to occur whilst the near-bed velocity was still offshore. The SSC peaked only slightly later than the TKE and therefore no evidence exists to support advection of pre-suspended sediment. Correlation tests are performed to assess the predictive capability of (a) a Bagnold-type model based on shear stress, (b) a similar model based on TKE, and (c) a model combining (a) and (b). When the data from the whole time series are used, the combined model improves r2 values over the shear stress model by up to 9%. If only data within bore events are included, then the improvement increases to over 55%, suggesting a significant effect of TKE on sediment transport across the bore. [Copyright &y& Elsevier]