Numerical modelling of tsunami-induced scour around a coastal dike

Coastal dikes are vital flood defence structures protecting nearshore from tsunamis, storm surges and extreme waves. However, the physical presence of a coastal structure can impact the hydro-sedimentary dynamics of the nearshore environment. Post-tsunami field surveys of the 2011 Tohoku tsunami indicated that the scour was the most dominant failure mode. When the overtopping plunging jet creates a scour hole in the leeward side of the structure, it causes structural failure in conjunction with other forces acting on the structure. This novel study focuses on 2D numerical model with RANS modelling approach of tsunami-like wave propagation and its associated scour process at the leeward of a coastal dike, obtained from turbulence-averaged Eulerian two-phase flow equations with the kinetic theory of granular flows for inter-granular stress models and a k-ε turbulence model. The numerical model results were validated using tsunami-induced scour laboratory data of 1:50 scale dike models. The results indicated good agreement with the predicted scour depths which were associated with the hydraulic conditions, sediment characteristics, and structure geometry. The current study will be beneficial in determining the compliance of predictive models with the experimental data and numerical analysis, which in turn can be used for validation of other models.