Morphodynamic Modelling of Flash Rip Current Driven Coastal Sediment Transport

Park, S.; Kim, D.-H., Yoo, H., 2020. Morphodynamic modelling of flash rip current driven coastal sediment transport. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1229-1234. Coconut Creek (Florida), ISSN 0749-0208. The characteristics of the sediment transport driven by flash rip currents at nearshore areas was investigated using a morphodynamic model coupled with a fully nonlinear Boussinesq-type model and a sediment transport model. Wave transform processes in surfzone such as shoaling, refraction, breaking, runup, and rundown processes were included in the numerical model. The vorticity and turbulent eddy viscosity were considered to account for rotational and turbulent flow characteristics. In addition, the horizontal density variation and bottom evolution caused by sediment transport were integrated into the fully nonlinear Boussinesq-type model. A fourth-order finite volume method, based on the MUSCL scheme with an approximate Riemann solver, was used to solve the governing equations. Uniform and parallel wave fields were simulated on a plain beach with a uniform sandbar with very small disturbance on the bathymetry. Because the wave generator was parallel to the beach, no significant longshore current and longshore sediment transport were generated. From the tested case, transient offshore-directed strong rip currents (the wave-averaged flow velocity 0.5 m/s) appeared in various locations. Turbid suspended sediment currents were also randomly generated by the waves and currents. The modelling results and analysis showed that the offshore direction sediment transport was strongly associated with the flash rip current generated within the surfzone.