A new computation method of bottom shear stress under Tsunami waves

The tsunami propagation in the river as well as sediment transport is highly affected by the bed stress beneath the wave. Unfortunately, most numerical models use an empirical method such as Manning's n, which was developed for steady flow. A new method in numerical modelling to assess bed stress and sediment transport induced by wave is developed based on the boundary layer approach. The boundary layer has a significant effect on the bed stress under unsteady flow. Bed stress under unsteady flow may exhibit phase shift and sign change to the free stream velocity. Recently, Simultaneous Coupling Method (SCM) was developed and verified by combining Shallow Water Equation (SWE) and k-ω model. The simplicity of SWE was maintained while k-ω model was used to assess the bed stress from the boundary layer. The velocity from SWE is assumed as the free stream velocity, which is used as the boundary condition for k-ω. The calculated bed stress from k-ω is used in SWE to obtain water depth and velocity. In this study, SCM is further developed by simulating a tsunami wave propagation around the Kitakami River mouth and verified using a laboratory experiment. The results show good comparison between the numerical and experimental.